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<span class="normal"> 978</span>
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<span class="normal"> 995</span>
<span class="normal"> 996</span>
<span class="normal"> 997</span>
<span class="normal"> 998</span>
<span class="normal"> 999</span>
<span class="normal">1000</span>
<span class="normal">1001</span>
<span class="normal">1002</span>
<span class="normal">1003</span>
<span class="normal">1004</span>
<span class="normal">1005</span>
<span class="normal">1006</span>
<span class="normal">1007</span>
<span class="normal">1008</span>
<span class="normal">1009</span>
<span class="normal">1010</span>
<span class="normal">1011</span>
<span class="normal">1012</span>
<span class="normal">1013</span>
<span class="normal">1014</span>
<span class="normal">1015</span>
<span class="normal">1016</span>
<span class="normal">1017</span>
<span class="normal">1018</span>
<span class="normal">1019</span>
<span class="normal">1020</span>
<span class="normal">1021</span>
<span class="normal">1022</span>
<span class="normal">1023</span>
<span class="normal">1024</span>
<span class="normal">1025</span>
<span class="normal">1026</span>
<span class="normal">1027</span>
<span class="normal">1028</span>
<span class="normal">1029</span>
<span class="normal">1030</span>
<span class="normal">1031</span>
<span class="normal">1032</span>
<span class="normal">1033</span>
<span class="normal">1034</span>
<span class="normal">1035</span>
<span class="normal">1036</span>
<span class="normal">1037</span>
<span class="normal">1038</span>
<span class="normal">1039</span>
<span class="normal">1040</span>
<span class="normal">1041</span>
<span class="normal">1042</span>
<span class="normal">1043</span>
<span class="normal">1044</span>
<span class="normal">1045</span>
<span class="normal">1046</span>
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<span class="normal">1048</span>
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<span class="normal">1062</span>
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<span class="normal">1064</span>
<span class="normal">1065</span>
<span class="normal">1066</span>
<span class="normal">1067</span>
<span class="normal">1068</span>
<span class="normal">1069</span>
<span class="normal">1070</span>
<span class="normal">1071</span>
<span class="normal">1072</span>
<span class="normal">1073</span>
<span class="normal">1074</span>
<span class="normal">1075</span>
<span class="normal">1076</span>
<span class="normal">1077</span>
<span class="normal">1078</span>
<span class="normal">1079</span>
<span class="normal">1080</span>
<span class="normal">1081</span>
<span class="normal">1082</span>
<span class="normal">1083</span>
<span class="normal">1084</span>
<span class="normal">1085</span>
<span class="normal">1086</span>
<span class="normal">1087</span>
<span class="normal">1088</span>
<span class="normal">1089</span>
<span class="normal">1090</span>
<span class="normal">1091</span>
<span class="normal">1092</span>
<span class="normal">1093</span>
<span class="normal">1094</span>
<span class="normal">1095</span>
<span class="normal">1096</span>
<span class="normal">1097</span>
<span class="normal">1098</span>
<span class="normal">1099</span>
<span class="normal">1100</span>
<span class="normal">1101</span>
<span class="normal">1102</span>
<span class="normal">1103</span>
<span class="normal">1104</span>
<span class="normal">1105</span>
<span class="normal">1106</span>
<span class="normal">1107</span>
<span class="normal">1108</span>
<span class="normal">1109</span>
<span class="normal">1110</span>
<span class="normal">1111</span>
<span class="normal">1112</span>
<span class="normal">1113</span>
<span class="normal">1114</span>
<span class="normal">1115</span>
<span class="normal">1116</span>
<span class="normal">1117</span>
<span class="normal">1118</span>
<span class="normal">1119</span>
<span class="normal">1120</span>
<span class="normal">1121</span>
<span class="normal">1122</span>
<span class="normal">1123</span>
<span class="normal">1124</span>
<span class="normal">1125</span>
<span class="normal">1126</span>
<span class="normal">1127</span>
<span class="normal">1128</span>
<span class="normal">1129</span>
<span class="normal">1130</span>
<span class="normal">1131</span>
<span class="normal">1132</span>
<span class="normal">1133</span>
<span class="normal">1134</span>
<span class="normal">1135</span>
<span class="normal">1136</span>
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<span class="normal">1140</span>
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<span class="normal">1160</span>
<span class="normal">1161</span>
<span class="normal">1162</span>
<span class="normal">1163</span>
<span class="normal">1164</span>
<span class="normal">1165</span>
<span class="normal">1166</span>
<span class="normal">1167</span>
<span class="normal">1168</span>
<span class="normal">1169</span>
<span class="normal">1170</span>
<span class="normal">1171</span>
<span class="normal">1172</span>
<span class="normal">1173</span>
<span class="normal">1174</span>
<span class="normal">1175</span>
<span class="normal">1176</span>
<span class="normal">1177</span>
<span class="normal">1178</span>
<span class="normal">1179</span>
<span class="normal">1180</span>
<span class="normal">1181</span>
<span class="normal">1182</span>
<span class="normal">1183</span>
<span class="normal">1184</span>
<span class="normal">1185</span>
<span class="normal">1186</span>
<span class="normal">1187</span>
<span class="normal">1188</span>
<span class="normal">1189</span>
<span class="normal">1190</span>
<span class="normal">1191</span>
<span class="normal">1192</span>
<span class="normal">1193</span>
<span class="normal">1194</span>
<span class="normal">1195</span>
<span class="normal">1196</span>
<span class="normal">1197</span>
<span class="normal">1198</span>
<span class="normal">1199</span>
<span class="normal">1200</span>
<span class="normal">1201</span>
<span class="normal">1202</span>
<span class="normal">1203</span>
<span class="normal">1204</span>
<span class="normal">1205</span>
<span class="normal">1206</span>
<span class="normal">1207</span>
<span class="normal">1208</span>
<span class="normal">1209</span>
<span class="normal">1210</span>
<span class="normal">1211</span>
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<span class="normal">1221</span>
<span class="normal">1222</span>
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<span class="normal">1226</span>
<span class="normal">1227</span>
<span class="normal">1228</span>
<span class="normal">1229</span>
<span class="normal">1230</span>
<span class="normal">1231</span>
<span class="normal">1232</span>
<span class="normal">1233</span>
<span class="normal">1234</span>
<span class="normal">1235</span>
<span class="normal">1236</span>
<span class="normal">1237</span>
<span class="normal">1238</span>
<span class="normal">1239</span>
<span class="normal">1240</span>
<span class="normal">1241</span>
<span class="normal">1242</span>
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<span class="normal">1248</span>
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<span class="normal">1264</span>
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<span class="normal">1270</span>
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<span class="normal">1300</span>
<span class="normal">1301</span>
<span class="normal">1302</span>
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<span class="normal">1311</span>
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<span class="normal">1941</span>
<span class="normal">1942</span>
<span class="normal">1943</span>
<span class="normal">1944</span>
<span class="normal">1945</span>
<span class="normal">1946</span>
<span class="normal">1947</span>
<span class="normal">1948</span>
<span class="normal">1949</span>
<span class="normal">1950</span>
<span class="normal">1951</span>
<span class="normal">1952</span>
<span class="normal">1953</span>
<span class="normal">1954</span>
<span class="normal">1955</span>
<span class="normal">1956</span>
<span class="normal">1957</span>
<span class="normal">1958</span>
<span class="normal">1959</span>
<span class="normal">1960</span>
<span class="normal">1961</span>
<span class="normal">1962</span>
<span class="normal">1963</span>
<span class="normal">1964</span>
<span class="normal">1965</span>
<span class="normal">1966</span>
<span class="normal">1967</span>
<span class="normal">1968</span>
<span class="normal">1969</span>
<span class="normal">1970</span>
<span class="normal">1971</span>
<span class="normal">1972</span>
<span class="normal">1973</span>
<span class="normal">1974</span>
<span class="normal">1975</span>
<span class="normal">1976</span>
<span class="normal">1977</span>
<span class="normal">1978</span>
<span class="normal">1979</span>
<span class="normal">1980</span>
<span class="normal">1981</span>
<span class="normal">1982</span>
<span class="normal">1983</span>
<span class="normal">1984</span>
<span class="normal">1985</span>
<span class="normal">1986</span>
<span class="normal">1987</span>
<span class="normal">1988</span>
<span class="normal">1989</span>
<span class="normal">1990</span>
<span class="normal">1991</span>
<span class="normal">1992</span>
<span class="normal">1993</span>
<span class="normal">1994</span>
<span class="normal">1995</span>
<span class="normal">1996</span>
<span class="normal">1997</span>
<span class="normal">1998</span>
<span class="normal">1999</span>
<span class="normal">2000</span>
<span class="normal">2001</span>
<span class="normal">2002</span>
<span class="normal">2003</span>
<span class="normal">2004</span>
<span class="normal">2005</span>
<span class="normal">2006</span>
<span class="normal">2007</span>
<span class="normal">2008</span>
<span class="normal">2009</span>
<span class="normal">2010</span>
<span class="normal">2011</span>
<span class="normal">2012</span>
<span class="normal">2013</span>
<span class="normal">2014</span>
<span class="normal">2015</span>
<span class="normal">2016</span>
<span class="normal">2017</span>
<span class="normal">2018</span>
<span class="normal">2019</span>
<span class="normal">2020</span>
<span class="normal">2021</span>
<span class="normal">2022</span>
<span class="normal">2023</span>
<span class="normal">2024</span>
<span class="normal">2025</span>
<span class="normal">2026</span>
<span class="normal">2027</span>
<span class="normal">2028</span>
<span class="normal">2029</span>
<span class="normal">2030</span>
<span class="normal">2031</span>
<span class="normal">2032</span>
<span class="normal">2033</span>
<span class="normal">2034</span>
<span class="normal">2035</span>
<span class="normal">2036</span>
<span class="normal">2037</span>
<span class="normal">2038</span>
<span class="normal">2039</span>
<span class="normal">2040</span>
<span class="normal">2041</span>
<span class="normal">2042</span>
<span class="normal">2043</span>
<span class="normal">2044</span>
<span class="normal">2045</span>
<span class="normal">2046</span>
<span class="normal">2047</span>
<span class="normal">2048</span>
<span class="normal">2049</span>
<span class="normal">2050</span>
<span class="normal">2051</span>
<span class="normal">2052</span>
<span class="normal">2053</span>
<span class="normal">2054</span>
<span class="normal">2055</span>
<span class="normal">2056</span>
<span class="normal">2057</span>
<span class="normal">2058</span>
<span class="normal">2059</span>
<span class="normal">2060</span>
<span class="normal">2061</span>
<span class="normal">2062</span>
<span class="normal">2063</span>
<span class="normal">2064</span>
<span class="normal">2065</span>
<span class="normal">2066</span>
<span class="normal">2067</span>
<span class="normal">2068</span>
<span class="normal">2069</span>
<span class="normal">2070</span>
<span class="normal">2071</span>
<span class="normal">2072</span>
<span class="normal">2073</span>
<span class="normal">2074</span>
<span class="normal">2075</span>
<span class="normal">2076</span>
<span class="normal">2077</span>
<span class="normal">2078</span>
<span class="normal">2079</span>
<span class="normal">2080</span>
<span class="normal">2081</span>
<span class="normal">2082</span>
<span class="normal">2083</span>
<span class="normal">2084</span>
<span class="normal">2085</span>
<span class="normal">2086</span>
<span class="normal">2087</span>
<span class="normal">2088</span>
<span class="normal">2089</span>
<span class="normal">2090</span>
<span class="normal">2091</span>
<span class="normal">2092</span>
<span class="normal">2093</span>
<span class="normal">2094</span>
<span class="normal">2095</span>
<span class="normal">2096</span>
<span class="normal">2097</span>
<span class="normal">2098</span>
<span class="normal">2099</span>
<span class="normal">2100</span>
<span class="normal">2101</span>
<span class="normal">2102</span>
<span class="normal">2103</span>
<span class="normal">2104</span>
<span class="normal">2105</span>
<span class="normal">2106</span>
<span class="normal">2107</span>
<span class="normal">2108</span>
<span class="normal">2109</span>
<span class="normal">2110</span>
<span class="normal">2111</span>
<span class="normal">2112</span>
<span class="normal">2113</span>
<span class="normal">2114</span>
<span class="normal">2115</span>
<span class="normal">2116</span>
<span class="normal">2117</span>
<span class="normal">2118</span>
<span class="normal">2119</span>
<span class="normal">2120</span>
<span class="normal">2121</span>
<span class="normal">2122</span>
<span class="normal">2123</span>
<span class="normal">2124</span>
<span class="normal">2125</span>
<span class="normal">2126</span>
<span class="normal">2127</span>
<span class="normal">2128</span>
<span class="normal">2129</span>
<span class="normal">2130</span>
<span class="normal">2131</span>
<span class="normal">2132</span>
<span class="normal">2133</span>
<span class="normal">2134</span>
<span class="normal">2135</span>
<span class="normal">2136</span>
<span class="normal">2137</span>
<span class="normal">2138</span>
<span class="normal">2139</span>
<span class="normal">2140</span>
<span class="normal">2141</span>
<span class="normal">2142</span>
<span class="normal">2143</span>
<span class="normal">2144</span>
<span class="normal">2145</span>
<span class="normal">2146</span>
<span class="normal">2147</span>
<span class="normal">2148</span>
<span class="normal">2149</span>
<span class="normal">2150</span>
<span class="normal">2151</span>
<span class="normal">2152</span>
<span class="normal">2153</span>
<span class="normal">2154</span>
<span class="normal">2155</span>
<span class="normal">2156</span>
<span class="normal">2157</span>
<span class="normal">2158</span>
<span class="normal">2159</span>
<span class="normal">2160</span>
<span class="normal">2161</span>
<span class="normal">2162</span>
<span class="normal">2163</span>
<span class="normal">2164</span>
<span class="normal">2165</span>
<span class="normal">2166</span>
<span class="normal">2167</span>
<span class="normal">2168</span>
<span class="normal">2169</span>
<span class="normal">2170</span>
<span class="normal">2171</span>
<span class="normal">2172</span>
<span class="normal">2173</span>
<span class="normal">2174</span>
<span class="normal">2175</span>
<span class="normal">2176</span>
<span class="normal">2177</span>
<span class="normal">2178</span>
<span class="normal">2179</span>
<span class="normal">2180</span>
<span class="normal">2181</span>
<span class="normal">2182</span>
<span class="normal">2183</span>
<span class="normal">2184</span>
<span class="normal">2185</span>
<span class="normal">2186</span>
<span class="normal">2187</span>
<span class="normal">2188</span>
<span class="normal">2189</span>
<span class="normal">2190</span>
<span class="normal">2191</span>
<span class="normal">2192</span>
<span class="normal">2193</span>
<span class="normal">2194</span>
<span class="normal">2195</span>
<span class="normal">2196</span>
<span class="normal">2197</span>
<span class="normal">2198</span>
<span class="normal">2199</span>
<span class="normal">2200</span>
<span class="normal">2201</span>
<span class="normal">2202</span>
<span class="normal">2203</span>
<span class="normal">2204</span>
<span class="normal">2205</span>
<span class="normal">2206</span>
<span class="normal">2207</span>
<span class="normal">2208</span>
<span class="normal">2209</span>
<span class="normal">2210</span>
<span class="normal">2211</span>
<span class="normal">2212</span>
<span class="normal">2213</span>
<span class="normal">2214</span>
<span class="normal">2215</span>
<span class="normal">2216</span>
<span class="normal">2217</span>
<span class="normal">2218</span>
<span class="normal">2219</span>
<span class="normal">2220</span>
<span class="normal">2221</span>
<span class="normal">2222</span>
<span class="normal">2223</span>
<span class="normal">2224</span>
<span class="normal">2225</span>
<span class="normal">2226</span>
<span class="normal">2227</span>
<span class="normal">2228</span>
<span class="normal">2229</span>
<span class="normal">2230</span>
<span class="normal">2231</span>
<span class="normal">2232</span>
<span class="normal">2233</span>
<span class="normal">2234</span>
<span class="normal">2235</span>
<span class="normal">2236</span>
<span class="normal">2237</span>
<span class="normal">2238</span>
<span class="normal">2239</span>
<span class="normal">2240</span>
<span class="normal">2241</span>
<span class="normal">2242</span>
<span class="normal">2243</span>
<span class="normal">2244</span>
<span class="normal">2245</span>
<span class="normal">2246</span>
<span class="normal">2247</span>
<span class="normal">2248</span>
<span class="normal">2249</span>
<span class="normal">2250</span>
<span class="normal">2251</span>
<span class="normal">2252</span>
<span class="normal">2253</span>
<span class="normal">2254</span>
<span class="normal">2255</span>
<span class="normal">2256</span>
<span class="normal">2257</span>
<span class="normal">2258</span>
<span class="normal">2259</span>
<span class="normal">2260</span>
<span class="normal">2261</span>
<span class="normal">2262</span>
<span class="normal">2263</span>
<span class="normal">2264</span>
<span class="normal">2265</span>
<span class="normal">2266</span>
<span class="normal">2267</span>
<span class="normal">2268</span>
<span class="normal">2269</span>
<span class="normal">2270</span>
<span class="normal">2271</span>
<span class="normal">2272</span>
<span class="normal">2273</span>
<span class="normal">2274</span>
<span class="normal">2275</span>
<span class="normal">2276</span>
<span class="normal">2277</span>
<span class="normal">2278</span>
<span class="normal">2279</span>
<span class="normal">2280</span>
<span class="normal">2281</span>
<span class="normal">2282</span>
<span class="normal">2283</span>
<span class="normal">2284</span>
<span class="normal">2285</span>
<span class="normal">2286</span>
<span class="normal">2287</span>
<span class="normal">2288</span>
<span class="normal">2289</span>
<span class="normal">2290</span>
<span class="normal">2291</span>
<span class="normal">2292</span>
<span class="normal">2293</span>
<span class="normal">2294</span></pre></div></td><td class="code"><div><pre><div id="l1" class="code_block"><span class="k">\chapter</span><span class="nb">{</span>Standard Predicates<span class="nb">}</span> <span class="k">\label</span><span class="nb">{</span>standard<span class="nb">}</span>
</div><div id="l2" class="code_block"><span class="c">%=============================================</span>
</div><div id="l3" class="code_block">
</div><div id="l4" class="code_block">Standard predicates are always available to the Prolog interpreter, and do
</div><div id="l5" class="code_block">not need to be imported or loaded explicitly as do other Prolog predicates.
</div><div id="l6" class="code_block">Our standard predicates are listed below.  Standard predicates whose 
</div><div id="l7" class="code_block">semantics depend on HiLog terms or on SLG evaluation are marked as 
</div><div id="l8" class="code_block"><span class="nb">{</span><span class="k">\sf</span> HiLog<span class="nb">}</span> or <span class="nb">{</span><span class="k">\sf</span> Tabling<span class="nb">}</span>.
</div><div id="l9" class="code_block">
</div><div id="l10" class="code_block">It is possible for the user to add standard predicates not provided
</div><div id="l11" class="code_block">in the standard release. See the section on Customizing XSB.
</div><div id="l12" class="code_block">
</div><div id="l13" class="code_block"><span class="k">\section</span><span class="nb">{</span>Input and Output<span class="nb">}</span>
</div><div id="l14" class="code_block">
</div><div id="l15" class="code_block">XSB has two levels of I/O: a higher level that supports DEC-10 and
</div><div id="l16" class="code_block">ISO-like file and stream handling; and a lower level that is based in
</div><div id="l17" class="code_block">XSB I/O ports.  This section describes higher-level I/O, while the
</div><div id="l18" class="code_block">lower-level is described in Volume 2 Section 1.5 of this manual.
</div><div id="l19" class="code_block">Presently, higher-level input and output operations bind a file
</div><div id="l20" class="code_block">identifier to the current input or output stream.  The semantics of
</div><div id="l21" class="code_block">the operations here is basically that of Edinbourough Prolog&#39;s <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l22" class="code_block">see/1<span class="nb">}</span> and <span class="nb">{</span><span class="k">\tt</span> tell/1<span class="nb">}</span>.  However, this interface has been extended to
</div><div id="l23" class="code_block">provide portability for programs written using the ISO standard, and
</div><div id="l24" class="code_block">includes predicates such as <span class="nb">{</span><span class="k">\tt</span> open/3<span class="nb">}</span>, <span class="nb">{</span><span class="k">\tt</span> close/1<span class="nb">}</span>, <span class="nb">{</span><span class="k">\tt</span> write/2<span class="nb">}</span>
</div><div id="l25" class="code_block">and so on.
</div><div id="l26" class="code_block">
</div><div id="l27" class="code_block">The default input and output streams are internally denoted by userin
</div><div id="l28" class="code_block">and userout 
</div><div id="l29" class="code_block">and they refer to the process&#39;es standard input and standard output
</div><div id="l30" class="code_block">streams).
</div><div id="l31" class="code_block">
</div><div id="l32" class="code_block">
</div><div id="l33" class="code_block"><span class="k">\subsection</span><span class="nb">{</span>File Handling<span class="nb">}</span>
</div><div id="l34" class="code_block"><span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l35" class="code_block"><span class="k">\ournewitem</span><span class="nb">{</span>set<span class="k">\_input</span>(+F)<span class="nb">}{</span>ISO<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>set<span class="k">\_input</span>/1<span class="nb">}}</span>
</div><div id="l36" class="code_block"><span class="k">\vspace</span><span class="nb">{</span>-7mm<span class="nb">}</span> 
</div><div id="l37" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>see(+F)<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>see/1<span class="nb">}}</span>
</div><div id="l38" class="code_block">    Makes file <span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> the current input stream. 
</div><div id="l39" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l40" class="code_block">    <span class="k">\item</span> If there is an open input stream associated with the file that 
</div><div id="l41" class="code_block">          has <span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> as its file name, and that stream was opened previously
</div><div id="l42" class="code_block">	  by <span class="nb">{</span><span class="k">\tt</span> see/1<span class="nb">}</span>, then it is made the current input stream.
</div><div id="l43" class="code_block">    <span class="k">\item</span> Otherwise, the specified file is opened for input and made the
</div><div id="l44" class="code_block">          current input stream. If the file does not exist, <span class="nb">{</span><span class="k">\tt</span> see/1<span class="nb">}</span> 
</div><div id="l45" class="code_block">	  fails.
</div><div id="l46" class="code_block">    <span class="k">\end</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l47" class="code_block">    Also note that different file names (that is, names which do not unify) 
</div><div id="l48" class="code_block">    represent different input streams (even if these different file names 
</div><div id="l49" class="code_block">    correspond to the same file).
</div><div id="l50" class="code_block">
</div><div id="l51" class="code_block">    The implementation of the ISO preducate <span class="nb">{</span><span class="k">\tt</span> set<span class="k">\_input</span>/1<span class="nb">}</span>, is
</div><div id="l52" class="code_block">    essentially that of <span class="nb">{</span><span class="k">\tt</span> see/1<span class="nb">}</span>.
</div><div id="l53" class="code_block">
</div><div id="l54" class="code_block">    Exceptions:
</div><div id="l55" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l56" class="code_block">    <span class="k">\item</span><span class="na">[{\tt permission\_error}]</span>
</div><div id="l57" class="code_block">    	File <span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> is directory or file is not readable. 
</div><div id="l58" class="code_block">    <span class="k">\item</span><span class="na">[{\tt instantiation\_error}]</span>
</div><div id="l59" class="code_block">    	<span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> is not instantiated at the time of call. 
</div><div id="l60" class="code_block">    <span class="k">\item</span><span class="na">[{\tt existence\_error}]</span>
</div><div id="l61" class="code_block">    	File <span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> does not exist. 
</div><div id="l62" class="code_block">    <span class="k">\item</span><span class="na">[{\tt domain\_error}]</span>
</div><div id="l63" class="code_block">    	<span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> is not an atomic file identifier
</div><div id="l64" class="code_block">    <span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l65" class="code_block">
</div><div id="l66" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>seeing(?F)<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>seeing/1<span class="nb">}}</span>
</div><div id="l67" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> is unified with the name of the current input stream.
</div><div id="l68" class="code_block">    This is exactly the same with predicate <span class="nb">{</span><span class="k">\tt</span> current<span class="k">\_input</span>/1<span class="nb">}</span>
</div><div id="l69" class="code_block">    described in Section~<span class="k">\ref</span><span class="nb">{</span>State<span class="nb">}</span>, and it is only provided for
</div><div id="l70" class="code_block">    upwards compatibility reasons.
</div><div id="l71" class="code_block">
</div><div id="l72" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>seen<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>seen/0<span class="nb">}}</span>
</div><div id="l73" class="code_block">    Closes the current input stream. 
</div><div id="l74" class="code_block">    Current input reverts to <span class="nb">{</span><span class="k">\tt</span> ``userin&#39;&#39;<span class="nb">}</span> (the standard input stream).
</div><div id="l75" class="code_block">
</div><div id="l76" class="code_block"><span class="k">\ournewitem</span><span class="nb">{</span>set<span class="k">\_output</span>(+F)<span class="nb">}{</span>ISO<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>set<span class="k">\_output</span>/1<span class="nb">}}</span>
</div><div id="l77" class="code_block"><span class="k">\vspace</span><span class="nb">{</span>-7mm<span class="nb">}</span> 
</div><div id="l78" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>tell(+F)<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>tell/1<span class="nb">}}</span>
</div><div id="l79" class="code_block">    Makes file <span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> the current output stream. 
</div><div id="l80" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l81" class="code_block">    <span class="k">\item</span> If there is an open output stream associated with <span class="nb">{</span><span class="k">\em</span> F<span class="nb">}</span>  
</div><div id="l82" class="code_block">          and that was opened previously 
</div><div id="l83" class="code_block">          by <span class="nb">{</span><span class="k">\tt</span> tell/1<span class="nb">}</span>, then that stream is made the current output 
</div><div id="l84" class="code_block">	  stream. 
</div><div id="l85" class="code_block">    <span class="k">\item</span> Otherwise, the specified file is opened for output and made the
</div><div id="l86" class="code_block">          current output stream. If the file does not exist, it is created.
</div><div id="l87" class="code_block">    <span class="k">\end</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l88" class="code_block">
</div><div id="l89" class="code_block">    Also note that different file names (that is, names which do not unify) 
</div><div id="l90" class="code_block">    represent different output streams (even if these different file names 
</div><div id="l91" class="code_block">    correspond to the same file).
</div><div id="l92" class="code_block">
</div><div id="l93" class="code_block">    The implementation of the ISO preducate <span class="nb">{</span><span class="k">\tt</span> set<span class="k">\_output</span>/1<span class="nb">}</span>, is
</div><div id="l94" class="code_block">    essentially that of <span class="nb">{</span><span class="k">\tt</span> tell/1<span class="nb">}</span>.
</div><div id="l95" class="code_block">
</div><div id="l96" class="code_block">    Exceptions:
</div><div id="l97" class="code_block">    <span class="k">\begin</span> <span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l98" class="code_block">    <span class="k">\item</span><span class="na">[{\tt permission\_error}]</span>
</div><div id="l99" class="code_block">	File <span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> does not have write permission, or is a directory.
</div><div id="l100" class="code_block">    <span class="k">\item</span><span class="na">[{\tt instantiation\_error}]</span>
</div><div id="l101" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> is uninstantiated.
</div><div id="l102" class="code_block">    <span class="k">\item</span><span class="na">[{\tt domain\_error}]</span>
</div><div id="l103" class="code_block">    	<span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> is not an atomic file identifier
</div><div id="l104" class="code_block">    <span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l105" class="code_block">
</div><div id="l106" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>telling(?F)<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>telling/1<span class="nb">}}</span>
</div><div id="l107" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> is unified with the name of the current output stream.
</div><div id="l108" class="code_block">    This predicate is exactly the same with predicate <span class="nb">{</span><span class="k">\tt</span> current<span class="k">\_output</span>/1<span class="nb">}</span>
</div><div id="l109" class="code_block">    described in Section~<span class="k">\ref</span><span class="nb">{</span>State<span class="nb">}</span>, and it is only provided for
</div><div id="l110" class="code_block">    upwards compatibility reasons.
</div><div id="l111" class="code_block">
</div><div id="l112" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>told<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>told/0<span class="nb">}}</span>
</div><div id="l113" class="code_block">    Closes the current output stream. 
</div><div id="l114" class="code_block">    Current output stream reverts to ``userout&#39;&#39; (the standard output stream).
</div><div id="l115" class="code_block">
</div><div id="l116" class="code_block"><span class="k">\ournewitem</span><span class="nb">{</span>open(+File,+Mode,-Stream)<span class="nb">}{</span>ISO<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>open/3<span class="nb">}}</span>
</div><div id="l117" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> open/1<span class="nb">}</span> creates a stream for the file designated in <span class="nb">{</span><span class="k">\em</span>
</div><div id="l118" class="code_block">    File<span class="nb">}</span>, and binds <span class="nb">{</span><span class="k">\em</span> Stream<span class="nb">}</span> to a structure representing that
</div><div id="l119" class="code_block">    stream.  <span class="nb">{</span><span class="k">\em</span> Mode<span class="nb">}</span> can be one of either <span class="nb">{</span><span class="k">\tt</span> read<span class="nb">}</span> to create an
</div><div id="l120" class="code_block">    input stream or <span class="nb">{</span><span class="k">\tt</span> write<span class="nb">}</span> or <span class="nb">{</span><span class="k">\tt</span> append<span class="nb">}</span> to create an output
</div><div id="l121" class="code_block">    stream.  If the mode is <span class="nb">{</span><span class="k">\tt</span> write<span class="nb">}</span>, the contents of <span class="nb">{</span><span class="k">\em</span> File<span class="nb">}</span>
</div><div id="l122" class="code_block">    are removed and <span class="nb">{</span><span class="k">\em</span> File<span class="nb">}</span> becomes a record of the output stream.
</div><div id="l123" class="code_block">    If the mode is <span class="nb">{</span><span class="k">\tt</span> append<span class="nb">}</span> the output stream is appended to the
</div><div id="l124" class="code_block">    contents of <span class="nb">{</span><span class="k">\em</span> File<span class="nb">}</span>.
</div><div id="l125" class="code_block">
</div><div id="l126" class="code_block">    Exceptions (<span class="nb">{</span><span class="k">\tt</span> read<span class="nb">}</span> mode)
</div><div id="l127" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l128" class="code_block">    <span class="k">\item</span><span class="na">[{\tt permission\_error}]</span>
</div><div id="l129" class="code_block">    	File <span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> is directory or file is not readable. 
</div><div id="l130" class="code_block">    <span class="k">\item</span><span class="na">[{\tt instantiation\_error}]</span>
</div><div id="l131" class="code_block">    	<span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> is not instantiated at the time of call. 
</div><div id="l132" class="code_block">    <span class="k">\item</span><span class="na">[{\tt existence\_error}]</span>
</div><div id="l133" class="code_block">    	File <span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> does not exist. 
</div><div id="l134" class="code_block">    <span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l135" class="code_block">
</div><div id="l136" class="code_block">    Exceptions (<span class="nb">{</span><span class="k">\tt</span> write<span class="nb">}</span> mode)
</div><div id="l137" class="code_block">    <span class="k">\begin</span> <span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l138" class="code_block">    <span class="k">\item</span><span class="na">[{\tt permission\_error}]</span>
</div><div id="l139" class="code_block">	File <span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> does not have write permission, or is a directory.
</div><div id="l140" class="code_block">    <span class="k">\item</span><span class="na">[{\tt instantiation\_error}]</span>
</div><div id="l141" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> is uninstantiated.
</div><div id="l142" class="code_block">    <span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l143" class="code_block">
</div><div id="l144" class="code_block"><span class="k">\ournewitem</span><span class="nb">{</span>open(+File,+Mode,-Stream.+Options)<span class="nb">}{</span>ISO<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>open/4<span class="nb">}}</span>
</div><div id="l145" class="code_block">
</div><div id="l146" class="code_block">	This predicate is implemented in XSB for partial ISO
</div><div id="l147" class="code_block">	compatability.  In the case where <span class="nb">{</span><span class="k">\tt</span> Options<span class="nb">}</span> is equal to <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l148" class="code_block">	[]<span class="nb">}</span>, <span class="nb">{</span><span class="k">\tt</span> open/4<span class="nb">}</span> is defined as <span class="nb">{</span><span class="k">\tt</span> open/3<span class="nb">}</span>, otherwise it
</div><div id="l149" class="code_block">	aborts.
</div><div id="l150" class="code_block">
</div><div id="l151" class="code_block">
</div><div id="l152" class="code_block"><span class="k">\ournewitem</span><span class="nb">{</span>close(+Stream)<span class="nb">}{</span>ISO<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>close/1<span class="nb">}}</span>
</div><div id="l153" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> close/1<span class="nb">}</span> closes the stream <span class="nb">{</span><span class="k">\em</span> Stream<span class="nb">}</span>.
</div><div id="l154" class="code_block">
</div><div id="l155" class="code_block"><span class="k">\ournewitem</span><span class="nb">{</span>close(+Stream.+Options)<span class="nb">}{</span>ISO<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>close/2<span class="nb">}}</span>
</div><div id="l156" class="code_block">
</div><div id="l157" class="code_block">	This predicate is implemented in XSB for partial ISO
</div><div id="l158" class="code_block">	compatability.  In the case where <span class="nb">{</span><span class="k">\tt</span> Options<span class="nb">}</span> is equal to
</div><div id="l159" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> []<span class="nb">}</span>, <span class="nb">{</span><span class="k">\tt</span> close/2<span class="nb">}</span> is defined as <span class="nb">{</span><span class="k">\tt</span> close/1<span class="nb">}</span>, otherwise
</div><div id="l160" class="code_block">	it aborts.
</div><div id="l161" class="code_block">
</div><div id="l162" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>file<span class="k">\_exists</span>(+F)<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>file<span class="k">\_exists</span>/1<span class="nb">}}</span>
</div><div id="l163" class="code_block">    Succeeds if file <span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> exists. <span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> must be instantiated to
</div><div id="l164" class="code_block">    an atom at the time of the call, or an error message is displayed on
</div><div id="l165" class="code_block">    the standard error stream and the predicate aborts.
</div><div id="l166" class="code_block">
</div><div id="l167" class="code_block">    Exceptions:
</div><div id="l168" class="code_block">    <span class="k">\begin</span> <span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l169" class="code_block">    <span class="k">\item</span><span class="na">[{\tt instantiation\_error}]</span>
</div><div id="l170" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> is uninstantiated.
</div><div id="l171" class="code_block">    <span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l172" class="code_block">
</div><div id="l173" class="code_block"><span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l174" class="code_block">
</div><div id="l175" class="code_block">
</div><div id="l176" class="code_block"><span class="k">\subsection</span><span class="nb">{</span>Character I/O<span class="nb">}</span>
</div><div id="l177" class="code_block"><span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l178" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>nl<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>nl/0<span class="nb">}}</span>
</div><div id="l179" class="code_block">    A new line character is sent to the current output stream.
</div><div id="l180" class="code_block">
</div><div id="l181" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>nl(+Stream)<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>nl/1<span class="nb">}}</span>
</div><div id="l182" class="code_block">    A new line character is sent to the designated output stream.
</div><div id="l183" class="code_block">
</div><div id="l184" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>get0(?N)<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>get0/1<span class="nb">}}</span> 
</div><div id="l185" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> N<span class="nb">}</span> is the ASCII code of the next character read from the
</div><div id="l186" class="code_block">    current input stream (regarded as a text stream). If the current
</div><div id="l187" class="code_block">    input stream reaches its end of file, a <span class="nb">{</span><span class="k">\tt</span> -1<span class="nb">}</span> is returned.
</div><div id="l188" class="code_block">
</div><div id="l189" class="code_block">    Compatibility Note:  Unlike other Prologs, such as C-Prolog, the input 
</div><div id="l190" class="code_block">    stream is not closed on encountering the end-of-file character.
</div><div id="l191" class="code_block">
</div><div id="l192" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>get(?N)<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>get/1<span class="nb">}}</span> 
</div><div id="l193" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> N<span class="nb">}</span> is the ASCII code of the next non-blank printable
</div><div id="l194" class="code_block">    character from the current input stream (regarded as a text
</div><div id="l195" class="code_block">    stream).  If the current input stream reaches its end of file, a
</div><div id="l196" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> -1<span class="nb">}</span> is returned.
</div><div id="l197" class="code_block">
</div><div id="l198" class="code_block">    Compatibility Note:  Unlike other Prologs, such as C-Prolog, the input 
</div><div id="l199" class="code_block">    stream is not closed on encountering the end-of-file character.
</div><div id="l200" class="code_block">
</div><div id="l201" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>get<span class="k">\_code</span>(?N)<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>get<span class="k">\_code</span>/1<span class="nb">}}</span>
</div><div id="l202" class="code_block"><span class="k">\vspace</span><span class="nb">{</span>-7mm<span class="nb">}</span> 
</div><div id="l203" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>get<span class="k">\_code</span>(+Stream,?N)<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>get<span class="k">\_code</span>/2<span class="nb">}}</span>
</div><div id="l204" class="code_block">   <span class="nb">{</span><span class="k">\tt</span> N<span class="nb">}</span> is the ASCII code of the next character from the current
</div><div id="l205" class="code_block">   input stream or from <span class="nb">{</span><span class="k">\tt</span> Stream<span class="nb">}</span>.  The semantics of these
</div><div id="l206" class="code_block">   predicates are based on that of <span class="nb">{</span><span class="k">\tt</span> get0/1<span class="nb">}</span> and do not conform in
</div><div id="l207" class="code_block">   all cases to the ISO standard.
</div><div id="l208" class="code_block">
</div><div id="l209" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>get<span class="k">\_char</span>(?Char)<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>get<span class="k">\_char</span>/1<span class="nb">}}</span>
</div><div id="l210" class="code_block"><span class="k">\vspace</span><span class="nb">{</span>-7mm<span class="nb">}</span> 
</div><div id="l211" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>get<span class="k">\_char</span>(+Stream,?Char)<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>get<span class="k">\_char</span>/2<span class="nb">}}</span>
</div><div id="l212" class="code_block">   <span class="nb">{</span><span class="k">\tt</span> Char<span class="nb">}</span> is the next ASCII character from the current input stream
</div><div id="l213" class="code_block">   or from <span class="nb">{</span><span class="k">\tt</span> Stream<span class="nb">}</span>.  The semantics of these predicates are based
</div><div id="l214" class="code_block">   on that of <span class="nb">{</span><span class="k">\tt</span> get0/1<span class="nb">}</span> and do not conform in all cases to the ISO
</div><div id="l215" class="code_block">   standard.
</div><div id="l216" class="code_block">
</div><div id="l217" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>put(+N)<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>put/1<span class="nb">}}</span>
</div><div id="l218" class="code_block">    Puts the ASCII character code <span class="nb">{</span><span class="k">\tt</span> N<span class="nb">}</span> to the current output stream.
</div><div id="l219" class="code_block">
</div><div id="l220" class="code_block">    Exceptions:
</div><div id="l221" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l222" class="code_block">    <span class="k">\item</span><span class="na">[{\tt instantiation\_error}]</span>
</div><div id="l223" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> N<span class="nb">}</span> is not instantiated at the time of the call.
</div><div id="l224" class="code_block">    <span class="k">\item</span><span class="na">[{\tt type\_error}]</span>
</div><div id="l225" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> N<span class="nb">}</span> is not an integer at the time of the call.
</div><div id="l226" class="code_block">    <span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l227" class="code_block">
</div><div id="l228" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>put<span class="k">\_code</span>(+N)<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>put<span class="k">\_code</span>/1<span class="nb">}}</span>
</div><div id="l229" class="code_block"><span class="k">\vspace</span><span class="nb">{</span>-7mm<span class="nb">}</span> 
</div><div id="l230" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>put<span class="k">\_code</span>(+Stream,+N)<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>put<span class="k">\_code</span>/2<span class="nb">}}</span>
</div><div id="l231" class="code_block">    Puts the ASCII character code <span class="nb">{</span><span class="k">\tt</span> N<span class="nb">}</span> to the current output stream
</div><div id="l232" class="code_block">    or to <span class="nb">{</span><span class="k">\tt</span> Stream<span class="nb">}</span>.  The semantics of these predicates are based
</div><div id="l233" class="code_block">    on that of <span class="nb">{</span><span class="k">\tt</span> put/1<span class="nb">}</span> and do not conform in all cases to the ISO
</div><div id="l234" class="code_block">    standard.
</div><div id="l235" class="code_block">
</div><div id="l236" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>put<span class="k">\_char</span>(+Char)<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>put<span class="k">\_char</span>/1<span class="nb">}}</span>
</div><div id="l237" class="code_block"><span class="k">\vspace</span><span class="nb">{</span>-7mm<span class="nb">}</span> 
</div><div id="l238" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>put<span class="k">\_char</span>(+Stream,+Char)<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>put<span class="k">\_char</span>/2<span class="nb">}}</span>
</div><div id="l239" class="code_block">    Puts the ASCII code of the character <span class="nb">{</span><span class="k">\tt</span> Char<span class="nb">}</span> to the current
</div><div id="l240" class="code_block">    output stream or to <span class="nb">{</span><span class="k">\tt</span> Stream<span class="nb">}</span>.  The semantics of these
</div><div id="l241" class="code_block">    predicates are based on that of <span class="nb">{</span><span class="k">\tt</span> put/1<span class="nb">}</span> and do not conform in
</div><div id="l242" class="code_block">    all cases to the ISO standard.
</div><div id="l243" class="code_block">
</div><div id="l244" class="code_block">
</div><div id="l245" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>tab(+N)<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>tab/1<span class="nb">}}</span>
</div><div id="l246" class="code_block">    Puts <span class="nb">{</span><span class="k">\tt</span> N<span class="nb">}</span> spaces to the current output stream. 
</div><div id="l247" class="code_block">
</div><div id="l248" class="code_block">    Exceptions:
</div><div id="l249" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l250" class="code_block">    <span class="k">\item</span><span class="na">[{\tt instantiation\_error}]</span>
</div><div id="l251" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> N<span class="nb">}</span> is not instantiated at the time of the call.
</div><div id="l252" class="code_block">    <span class="k">\item</span><span class="na">[{\tt type\_error}]</span>
</div><div id="l253" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> N<span class="nb">}</span> is not an integer at the time of the call.
</div><div id="l254" class="code_block">    <span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l255" class="code_block"><span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l256" class="code_block">
</div><div id="l257" class="code_block"><span class="k">\subsection</span><span class="nb">{</span>Term I/O<span class="nb">}</span>
</div><div id="l258" class="code_block"><span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l259" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>read(?Term)<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>read/1<span class="nb">}}</span>
</div><div id="l260" class="code_block">    A HiLog term is read from the current or designated input stream,
</div><div id="l261" class="code_block">    and unified with <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> according to the operator declarations
</div><div id="l262" class="code_block">    in force.  (See Section~<span class="k">\ref</span><span class="nb">{</span>TermSyntax<span class="nb">}</span> for the definition and
</div><div id="l263" class="code_block">    syntax of HiLog terms). The term must be delimited by a full stop
</div><div id="l264" class="code_block">    (i.e. a ``.&#39;&#39; followed by a carriage-return, space or tab).
</div><div id="l265" class="code_block">    Predicate <span class="nb">{</span><span class="k">\tt</span> read/1<span class="nb">}</span> does not return until a valid HiLog term is
</div><div id="l266" class="code_block">    successfully read; that is, in the presense of syntax errors <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l267" class="code_block">    read/1<span class="nb">}</span> does not fail but continues reading terms until a term
</div><div id="l268" class="code_block">    with no syntax errors is encountered.  If a call to <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l269" class="code_block">    read(Term)<span class="nb">}</span> causes the end of the current input stream to be
</div><div id="l270" class="code_block">    reached, variable <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> is unified with the term <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l271" class="code_block">    end<span class="k">\_of\_file</span><span class="nb">}</span>.  In that case, further calls to <span class="nb">{</span><span class="k">\tt</span> read/1<span class="nb">}</span> for
</div><div id="l272" class="code_block">    the same input stream will cause an error failure.
</div><div id="l273" class="code_block">
</div><div id="l274" class="code_block">    Exceptions:
</div><div id="l275" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l276" class="code_block">    <span class="k">\item</span><span class="na">[{\tt existence\_error}]</span>
</div><div id="l277" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> end<span class="k">\_of\_file</span><span class="nb">}</span> is reached before the current term is read.
</div><div id="l278" class="code_block">    <span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l279" class="code_block">
</div><div id="l280" class="code_block"><span class="c">%--------</span>
</div><div id="l281" class="code_block">
</div><div id="l282" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>read(+Stream, ?Term)<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>read/2<span class="nb">}}</span>
</div><div id="l283" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> read/2<span class="nb">}</span> has the same behavior as <span class="nb">{</span><span class="k">\tt</span> read/1<span class="nb">}</span> but the
</div><div id="l284" class="code_block">	input stream is explicitly designated using the first argument.
</div><div id="l285" class="code_block">
</div><div id="l286" class="code_block"><span class="c">%--------</span>
</div><div id="l287" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>read<span class="k">\_term</span>(?Term,?OptionsList)<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>read<span class="k">\_term</span>/2<span class="nb">}}</span>
</div><div id="l288" class="code_block"><span class="c">%</span>
</div><div id="l289" class="code_block">A term is read from the current input stream as in <span class="nb">{</span><span class="k">\tt</span> read/1<span class="nb">}</span>; but
</div><div id="l290" class="code_block"><span class="nb">{</span><span class="k">\tt</span> OptionsList<span class="nb">}</span> is a (possibly empty) list of <span class="nb">{</span><span class="k">\em</span> read options<span class="nb">}</span>
</div><div id="l291" class="code_block">that specifie additional behavior.  The read options include
</div><div id="l292" class="code_block"><span class="k">\begin</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l293" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> variables(Vars)<span class="nb">}</span>: once a term has been read, <span class="nb">{</span><span class="k">\tt</span> Vars<span class="nb">}</span> is a
</div><div id="l294" class="code_block">list of the variables in the term, in left-to-right order. 
</div><div id="l295" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> variable<span class="k">\_names</span>(VN<span class="k">\_List</span>)<span class="nb">}</span>: once a term has been read <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l296" class="code_block">VN<span class="k">\_List</span><span class="nb">}</span> is a list of non-anonymous variables in the term.  The
</div><div id="l297" class="code_block">elements of the list have the form <span class="nb">{</span><span class="k">\tt</span> A = V<span class="nb">}</span> where <span class="nb">{</span><span class="k">\tt</span> V<span class="nb">}</span> is a
</div><div id="l298" class="code_block">non-anonymous variable of the term, and <span class="nb">{</span><span class="k">\tt</span> A<span class="nb">}</span> is the string used to
</div><div id="l299" class="code_block">denote the variable in the input stream.
</div><div id="l300" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> singletons(VS<span class="k">\_List</span>)<span class="nb">}</span>: once a term has been read <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l301" class="code_block">VN<span class="k">\_List</span><span class="nb">}</span> is a list of the non-anonymous <span class="nb">{</span><span class="k">\tt</span> singleton<span class="nb">}</span> varables in
</div><div id="l302" class="code_block">the term.  The elements of the list have the form <span class="nb">{</span><span class="k">\tt</span> A = V<span class="nb">}</span> where
</div><div id="l303" class="code_block"><span class="nb">{</span><span class="k">\tt</span> V<span class="nb">}</span> is a non-anonymous variable of the term, and <span class="nb">{</span><span class="k">\tt</span> A<span class="nb">}</span> is the
</div><div id="l304" class="code_block">string used to denote the variable in the input stream.
</div><div id="l305" class="code_block"><span class="k">\end</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l306" class="code_block">
</div><div id="l307" class="code_block">    Exceptions:
</div><div id="l308" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l309" class="code_block">    <span class="k">\item</span><span class="na">[{\tt instantiation\_error}]</span>
</div><div id="l310" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> OptionsList<span class="nb">}</span> is a variable, or is a list containing a
</div><div id="l311" class="code_block">			variable element.
</div><div id="l312" class="code_block">    <span class="k">\item</span><span class="na">[{\tt type\_error}]</span>
</div><div id="l313" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> OptionsList<span class="nb">}</span> is neither a list nor a variable
</div><div id="l314" class="code_block">    <span class="k">\item</span><span class="na">[{\tt domain\_error}]</span>
</div><div id="l315" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> OptionsList<span class="nb">}</span> contains a non-variable element that is not
</div><div id="l316" class="code_block">	a read option.
</div><div id="l317" class="code_block">    <span class="k">\item</span><span class="na">[{\tt existence\_error}]</span>
</div><div id="l318" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> end<span class="k">\_of\_file</span><span class="nb">}</span> is reached before the current term is read.
</div><div id="l319" class="code_block">    <span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l320" class="code_block">
</div><div id="l321" class="code_block"><span class="c">%--------</span>
</div><div id="l322" class="code_block">
</div><div id="l323" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>read<span class="k">\_term</span>(+Stream, ?Term,?OptionsList)<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>read<span class="k">\_term</span>/3<span class="nb">}}</span>
</div><div id="l324" class="code_block"><span class="c">%</span>
</div><div id="l325" class="code_block"><span class="nb">{</span><span class="k">\tt</span> read<span class="k">\_term</span>/3<span class="nb">}</span> has the same behavior as <span class="nb">{</span><span class="k">\tt</span> read<span class="k">\_term</span>/2<span class="nb">}</span> but
</div><div id="l326" class="code_block">the input stream is explicitly designated using the first argument.
</div><div id="l327" class="code_block">
</div><div id="l328" class="code_block">Exceptions are the same as <span class="nb">{</span><span class="k">\tt</span> read<span class="k">\_term</span>/2<span class="nb">}</span>, but with the addition:
</div><div id="l329" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l330" class="code_block">    <span class="k">\item</span><span class="na">[{\tt instantiation\_error}]</span>
</div><div id="l331" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> Strean<span class="nb">}</span> is a variable.
</div><div id="l332" class="code_block">    <span class="k">\item</span><span class="na">[{\tt domain\_error}]</span>
</div><div id="l333" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> Stream<span class="nb">}</span> is not an XSB stream (currently an atom).
</div><div id="l334" class="code_block">    <span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l335" class="code_block">
</div><div id="l336" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>write(?Term)<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>write/1<span class="nb">}}</span>
</div><div id="l337" class="code_block">    The HiLog term <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> is written to the current output stream, 
</div><div id="l338" class="code_block">    according to the operator declarations in force.  Any uninstantiated 
</div><div id="l339" class="code_block">    subterm of term <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> is written as an anonymous variable (an 
</div><div id="l340" class="code_block">    underscore followed by a non-negative integer).  
</div><div id="l341" class="code_block">
</div><div id="l342" class="code_block">    All <span class="nb">{</span><span class="k">\em</span> proper HiLog terms<span class="nb">}</span> (HiLog terms which are not also Prolog terms) 
</div><div id="l343" class="code_block">    are not written in their internal Prolog representation.  Predicate 
</div><div id="l344" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> write/1<span class="nb">}</span> always succeeds without producing an error.
</div><div id="l345" class="code_block">
</div><div id="l346" class="code_block">    The HiLog terms that are output by <span class="nb">{</span><span class="k">\tt</span> write/1<span class="nb">}</span> cannot in general be 
</div><div id="l347" class="code_block">    read back using <span class="nb">{</span><span class="k">\tt</span> read/1<span class="nb">}</span>.  This happens for two reasons:
</div><div id="l348" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l349" class="code_block">    <span class="k">\item</span> The atoms appearing in term <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> are not quoted. In that case 
</div><div id="l350" class="code_block">          the user must use <span class="nb">{</span><span class="k">\tt</span> writeq/1<span class="nb">}</span> or 
</div><div id="l351" class="code_block">          <span class="nb">{</span><span class="k">\tt</span> write<span class="k">\_canonical</span>/1<span class="nb">}</span> described below, which quote around atoms 
</div><div id="l352" class="code_block">          whenever necessary.
</div><div id="l353" class="code_block">    <span class="k">\item</span> The output of <span class="nb">{</span><span class="k">\tt</span> write/1<span class="nb">}</span> is not terminated by a full-stop;
</div><div id="l354" class="code_block">          therefore, if the user wants the term to be accepted as input to
</div><div id="l355" class="code_block">          <span class="nb">{</span><span class="k">\tt</span> read/1<span class="nb">}</span>, the terminating full-stop must be explicitly sent 
</div><div id="l356" class="code_block">          to the current output stream. 
</div><div id="l357" class="code_block">    <span class="k">\end</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l358" class="code_block">
</div><div id="l359" class="code_block">    Predicate <span class="nb">{</span><span class="k">\tt</span> write/1<span class="nb">}</span> treats terms of the form <span class="k">\verb</span>|&#39;<span class="s">$</span><span class="nb">VAR&#39;</span><span class="o">(</span><span class="nb">N</span><span class="o">)</span><span class="nb">|</span>
</div><div id="l360" class="code_block"><span class="nb">    specially: it writes {</span><span class="nv">\tt</span><span class="nb"> &#39;A&#39;} if {</span><span class="nv">\tt</span><span class="nb"> N}</span><span class="o">=</span><span class="m">0</span><span class="nb">, {</span><span class="nv">\tt</span><span class="nb"> &#39;B&#39;} if {</span><span class="nv">\tt</span>
</div><div id="l361" class="code_block"><span class="nb">    N}</span><span class="o">=</span><span class="m">1</span><span class="nb">, </span><span class="s">$</span><span class="k">\ldots</span><span class="s">$</span><span class="nb">, {</span><span class="nv">\tt</span><span class="nb"> &#39;Z&#39;} if {</span><span class="nv">\tt</span><span class="nb"> N}</span><span class="o">=</span><span class="m">25</span><span class="nb">, {</span><span class="nv">\tt</span><span class="nb"> &#39;A</span><span class="m">1</span><span class="nb">&#39;} if {</span><span class="nv">\tt</span><span class="nb"> N}</span><span class="o">=</span><span class="m">26</span><span class="nb">,</span>
</div><div id="l362" class="code_block"><span class="nb">    etc.  Terms of this form are generated by {</span><span class="nv">\tt</span><span class="nb"> numbervars</span><span class="o">/[</span><span class="m">1</span><span class="nb">,</span><span class="m">3</span><span class="o">]</span><span class="nb">}</span>
</div><div id="l363" class="code_block"><span class="nb">    described in the section {</span><span class="nv">\it</span><span class="nb"> Library Utilities} in Volume </span><span class="m">2</span><span class="nb">.</span>
</div><div id="l364" class="code_block"><span class="nb">    </span><span class="nv">\verb</span><span class="nb">|&#39;</span><span class="s">$</span>VAR&#39;(-1)| is written as the anonymous variable <span class="k">\verb</span>|&#39;<span class="nb">_</span>&#39;|.
</div><div id="l365" class="code_block">
</div><div id="l366" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>write(+Stream, ?Term)<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>write/2<span class="nb">}}</span>
</div><div id="l367" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> write/2<span class="nb">}</span> has the same behavior as <span class="nb">{</span><span class="k">\tt</span> write/1<span class="nb">}</span> but the
</div><div id="l368" class="code_block">	output stream is explicitly designated using the first argument.
</div><div id="l369" class="code_block">
</div><div id="l370" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>write<span class="k">\_term</span>(?Term,+Options)<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>write<span class="k">\_term</span>/2<span class="nb">}}</span>
</div><div id="l371" class="code_block"><span class="k">\vspace</span><span class="nb">{</span>-7mm<span class="nb">}</span> 
</div><div id="l372" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>write<span class="k">\_term</span>(+Stream, ?Term,+Options)<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>write<span class="k">\_term</span>/3<span class="nb">}}</span>
</div><div id="l373" class="code_block">
</div><div id="l374" class="code_block">    Outputs <span class="nb">{</span><span class="k">\tt</span> +Term<span class="nb">}</span> to the current output (<span class="nb">{</span><span class="k">\tt</span> write<span class="k">\_term</span>/2<span class="nb">}</span>) or
</div><div id="l375" class="code_block">    to <span class="nb">{</span><span class="k">\tt</span> Stream<span class="nb">}</span> (<span class="nb">{</span><span class="k">\tt</span> write<span class="k">\_term</span>/3<span class="nb">}</span>) according to the list of
</div><div id="l376" class="code_block">    write options, <span class="nb">{</span><span class="k">\tt</span> Options<span class="nb">}</span>.  The current set of write options
</div><div id="l377" class="code_block">    which form a superset of the ISO-standard write options, are as
</div><div id="l378" class="code_block">    follows:
</div><div id="l379" class="code_block"><span class="c">%</span>
</div><div id="l380" class="code_block"><span class="k">\begin</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l381" class="code_block"><span class="c">%</span>
</div><div id="l382" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> quoted(+Bool)<span class="nb">}</span>.  If <span class="nb">{</span><span class="k">\tt</span> Bool = true<span class="nb">}</span>, then atoms and
</div><div id="l383" class="code_block">    functors that can&#39;t be read back by <span class="nb">{</span><span class="k">\tt</span> read/1<span class="nb">}</span> are quoted, if
</div><div id="l384" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> Bool = false<span class="nb">}</span>, each atom and functor is written as its
</div><div id="l385" class="code_block">    unquoted name. Default value is <span class="nb">{</span><span class="k">\tt</span> false<span class="nb">}</span>.
</div><div id="l386" class="code_block"><span class="c">%</span>
</div><div id="l387" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> ignore<span class="k">\_ops</span>(+Bool)<span class="nb">}</span>. If <span class="nb">{</span><span class="k">\tt</span> Bool = true<span class="nb">}</span> each compound term
</div><div id="l388" class="code_block">is output in functional notation; curly brackets and list braces are
</div><div id="l389" class="code_block">ignored, as are all explicitly defined operators.  If <span class="nb">{</span><span class="k">\tt</span> Bool =
</div><div id="l390" class="code_block">false<span class="nb">}</span>, curly bracketed notation and list notation is enabled when
</div><div id="l391" class="code_block">outputing compound terms, and all other operator notation is
</div><div id="l392" class="code_block">enabed.  Default value is <span class="nb">{</span><span class="k">\tt</span> false<span class="nb">}</span>.
</div><div id="l393" class="code_block"><span class="c">%</span>
</div><div id="l394" class="code_block"> <span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> numbervars(+Bool)<span class="nb">}</span>.  If <span class="nb">{</span><span class="k">\tt</span> Bool = true<span class="nb">}</span>, a term of the
</div><div id="l395" class="code_block">form <span class="nb">{</span><span class="k">\tt</span> &#39;<span class="k">\$</span>VAR&#39;(N)<span class="nb">}</span> where <span class="nb">{</span><span class="k">\tt</span> N<span class="nb">}</span> is an integer, is output as a
</div><div id="l396" class="code_block">variable name consisting of a capital letter possibly followed by an
</div><div id="l397" class="code_block">integer.  A term of the form <span class="nb">{</span><span class="k">\tt</span> &#39;<span class="k">\$</span>VAR&#39;(Atom)<span class="nb">}</span> where <span class="nb">{</span><span class="k">\tt</span> Atom<span class="nb">}</span> is an
</div><div id="l398" class="code_block">atom, is output as itself (without quotes).  Finally, a term of the
</div><div id="l399" class="code_block">form <span class="nb">{</span><span class="k">\tt</span> &#39;<span class="k">\$</span>VAR&#39;(String)<span class="nb">}</span> where <span class="nb">{</span><span class="k">\tt</span> String<span class="nb">}</span> is a character string, is
</div><div id="l400" class="code_block">output as the atom corresponding to this character string.  If
</div><div id="l401" class="code_block"><span class="nb">{</span><span class="k">\tt</span> bool<span class="nb">}</span> is <span class="nb">{</span><span class="k">\tt</span> false<span class="nb">}</span> this cases are not treated in any special
</div><div id="l402" class="code_block">way.  Default value is <span class="nb">{</span><span class="k">\tt</span> false<span class="nb">}</span>.
</div><div id="l403" class="code_block"><span class="c">%</span>
</div><div id="l404" class="code_block"><span class="c">% See predicates {\tt numbervars/3} and {\tt prettyvars/1}.  </span>
</div><div id="l405" class="code_block"><span class="c">%</span>
</div><div id="l406" class="code_block"><span class="c">% TLS: need predicate portray attribute, if we dont have it.</span>
</div><div id="l407" class="code_block"><span class="c">%</span>
</div><div id="l408" class="code_block"><span class="k">\comment</span><span class="nb">{</span>
</div><div id="l409" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> portrayed(+Bool)<span class="nb">}</span>. If <span class="nb">{</span><span class="k">\tt</span> Bool = true<span class="nb">}</span>, then a call is made
</div><div id="l410" class="code_block">to the predicate @pred<span class="nb">{</span>portray/1<span class="nb">}</span>, to
</div><div id="l411" class="code_block">provide the user handlers for pretty printing some terms.  <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l412" class="code_block">portray<span class="nb">_</span>attribute/1<span class="nb">}</span> is called whenever an attributed variable is to
</div><div id="l413" class="code_block">be printed, <span class="nb">{</span><span class="k">\tt</span> portray/1<span class="nb">}</span> is called whenever a non-variable term is
</div><div id="l414" class="code_block">to be printed.  If either call succeeds, then it is assumed that the
</div><div id="l415" class="code_block">term has been output, else it is printed as usual.  If <span class="nb">{</span><span class="k">\tt</span> bool<span class="nb">}</span> is
</div><div id="l416" class="code_block"><span class="nb">{</span><span class="k">\tt</span> false<span class="nb">}</span>, these predicates are not called. Default value is <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l417" class="code_block">false<span class="nb">}</span>.  This option is set by the toplevel when writting the final
</div><div id="l418" class="code_block">values of variables, and by the debugging package when writting the
</div><div id="l419" class="code_block">goals in the tracing messages.  Thus you can vary the forms of these
</div><div id="l420" class="code_block">messages if you wish.
</div><div id="l421" class="code_block"><span class="nb">}</span>
</div><div id="l422" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> max<span class="k">\_depth</span>(+Depth)<span class="nb">}</span>. <span class="nb">{</span><span class="k">\tt</span> Depth<span class="nb">}</span> is a positive integer or
</div><div id="l423" class="code_block">zero. If positive, it denotes the depth limit on printing compound
</div><div id="l424" class="code_block">terms. If <span class="nb">{</span><span class="k">\tt</span> Depth<span class="nb">}</span> is zero, there is no limit. Default value is
</div><div id="l425" class="code_block"><span class="nb">{</span><span class="k">\tt</span> 0<span class="nb">}</span> (no limit).
</div><div id="l426" class="code_block"><span class="c">%</span>
</div><div id="l427" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> priority(+Prio)<span class="nb">}</span> <span class="nb">{</span><span class="k">\tt</span> Prio<span class="nb">}</span> is an integer between 1 and
</div><div id="l428" class="code_block">1200.  If the term to be printed has higher priority than <span class="nb">{</span><span class="k">\tt</span> Prio<span class="nb">}</span>,
</div><div id="l429" class="code_block">it will be printed parenthesized.  Default value is 1200 (no term
</div><div id="l430" class="code_block">parenthesized).
</div><div id="l431" class="code_block"><span class="k">\end</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l432" class="code_block">
</div><div id="l433" class="code_block">From the following examples it can be seen that <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l434" class="code_block">write<span class="k">\_term</span>/<span class="k">\{</span>2,3<span class="k">\}</span><span class="nb">}</span> can duplicate the behavior of a number of other
</div><div id="l435" class="code_block">I/O predicates such as <span class="nb">{</span><span class="k">\tt</span> writeq/<span class="k">\{</span>1,2<span class="k">\}</span><span class="nb">}</span>, <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l436" class="code_block">write<span class="k">\_canonical</span>/<span class="k">\{</span>1,2<span class="k">\}</span><span class="nb">}</span>, etc.
</div><div id="l437" class="code_block"><span class="nb">{</span><span class="k">\small</span>
</div><div id="l438" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l439" class="code_block">
</div><div id="l440" class="code_block">| ?- write<span class="nb">_</span>term(f(1+2,&#39;A&#39;,&quot;string&quot;,&#39;<span class="s">$</span><span class="nb">VAR&#39;</span><span class="o">(</span><span class="m">3</span><span class="o">)</span><span class="nb">,&#39;</span><span class="s">$</span>VAR&#39;(&#39;Temp&#39;),(multifile foo)),[]).
</div><div id="l441" class="code_block">f(1 + 2,A,&quot;string&quot;,<span class="s">$</span><span class="nb">VAR</span><span class="o">(</span><span class="m">3</span><span class="o">)</span><span class="nb">,</span><span class="s">$</span>VAR(Temp),(multifile foo))
</div><div id="l442" class="code_block">yes
</div><div id="l443" class="code_block">
</div><div id="l444" class="code_block">| ?- write<span class="nb">_</span>term(f(1+2,&#39;A&#39;,&quot;string&quot;,&#39;<span class="s">$</span><span class="nb">VAR&#39;</span><span class="o">(</span><span class="m">3</span><span class="o">)</span><span class="nb">,&#39;</span><span class="s">$</span>VAR&#39;(&#39;Temp&#39;),(multifile foo)),
</div><div id="l445" class="code_block">                [quoted(true)]).
</div><div id="l446" class="code_block">f(1 + 2,&#39;A&#39;,&quot;string&quot;,&#39;<span class="s">$</span><span class="nb">VAR&#39;</span><span class="o">(</span><span class="m">3</span><span class="o">)</span><span class="nb">,&#39;</span><span class="s">$</span>VAR&#39;(&#39;Temp&#39;),(multifile foo))
</div><div id="l447" class="code_block">yes
</div><div id="l448" class="code_block">
</div><div id="l449" class="code_block">| ?- write<span class="nb">_</span>term(f(1+2,&#39;A&#39;,&quot;string&quot;,&#39;<span class="s">$</span><span class="nb">VAR&#39;</span><span class="o">(</span><span class="m">3</span><span class="o">)</span><span class="nb">,&#39;</span><span class="s">$</span>VAR&#39;(&#39;Temp&#39;),(multifile foo)),
</div><div id="l450" class="code_block">                [quoted(true),ignore<span class="nb">_</span>ops(true),numbervars(true)]).
</div><div id="l451" class="code_block">f(+(1,2),&#39;A&#39;,&#39;.&#39;(115,&#39;.&#39;(116,&#39;.&#39;(114,&#39;.&#39;(105,&#39;.&#39;(110,&#39;.&#39;(103,[])))))),D,Temp,(multifile foo))
</div><div id="l452" class="code_block">yes
</div><div id="l453" class="code_block">
</div><div id="l454" class="code_block">| ?- write<span class="nb">_</span>term(f(1+2,&#39;A&#39;,&quot;string&quot;,&#39;<span class="s">$</span><span class="nb">VAR&#39;</span><span class="o">(</span><span class="m">3</span><span class="o">)</span><span class="nb">,&#39;</span><span class="s">$</span>VAR&#39;(&#39;Temp&#39;),(multifile foo)),
</div><div id="l455" class="code_block">                [quoted(true),ignore<span class="nb">_</span>ops(true),numbervars(true),priority(1000)]).
</div><div id="l456" class="code_block">f(+(1,2),&#39;A&#39;,&#39;.&#39;(115,&#39;.&#39;(116,&#39;.&#39;(114,&#39;.&#39;(105,&#39;.&#39;(110,&#39;.&#39;(103,[])))))),D,Temp,multifile(foo))
</div><div id="l457" class="code_block">yes
</div><div id="l458" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l459" class="code_block"><span class="nb">}</span>
</div><div id="l460" class="code_block">
</div><div id="l461" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>writeln(?Term)<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>writeln/1<span class="nb">}}</span>
</div><div id="l462" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> writeln(Term)<span class="nb">}</span> can be defined as <span class="nb">{</span><span class="k">\tt</span> write(Term), nl<span class="nb">}</span>.
</div><div id="l463" class="code_block">
</div><div id="l464" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>writeln(+Stream,?Term)<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>writeln/2<span class="nb">}}</span>
</div><div id="l465" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> writeln(Term)<span class="nb">}</span> can be defined as <span class="nb">{</span><span class="k">\tt</span> write(Stream,Term),
</div><div id="l466" class="code_block">    nl(Stream)<span class="nb">}</span>.
</div><div id="l467" class="code_block">
</div><div id="l468" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>display(?Term)<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>display/1<span class="nb">}}</span>
</div><div id="l469" class="code_block">    The HiLog term <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> is displayed on the terminal (standard output 
</div><div id="l470" class="code_block">    stream), according to the operator declarations in force. In other words,
</div><div id="l471" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> display/1<span class="nb">}</span> is similar to <span class="nb">{</span><span class="k">\tt</span> write/1<span class="nb">}</span> but the result is always
</div><div id="l472" class="code_block">    written on <span class="nb">{</span><span class="k">\tt</span> ``userout&#39;&#39;<span class="nb">}</span><span class="k">\@</span>.  Like <span class="nb">{</span><span class="k">\tt</span> write/1<span class="nb">}</span>, <span class="nb">{</span><span class="k">\tt</span> display/1<span class="nb">}</span> 
</div><div id="l473" class="code_block">    always succeeds without producing an error. After returning from a call 
</div><div id="l474" class="code_block">    to this predicate, the current output stream remains unchanged.
</div><div id="l475" class="code_block">
</div><div id="l476" class="code_block"><span class="k">\ournewitem</span><span class="nb">{</span>write<span class="k">\_prolog</span>(?Term)<span class="nb">}{</span>HiLog<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>write<span class="k">\_prolog</span>/1<span class="nb">}}</span>
</div><div id="l477" class="code_block">    This predicate acts as does <span class="nb">{</span><span class="k">\tt</span> write/1<span class="nb">}</span> except that
</div><div id="l478" class="code_block">    any HiLog term <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> is written as a Prolog term. 
</div><div id="l479" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> write<span class="k">\_prolog</span>/1<span class="nb">}</span> outputs <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> according to the operator 
</div><div id="l480" class="code_block">    declarations
</div><div id="l481" class="code_block">    in force.  Because of this, it differs from <span class="nb">{</span><span class="k">\tt</span> write<span class="k">\_canonical</span>/1<span class="nb">}</span> 
</div><div id="l482" class="code_block">    described below, despite the fact that both predicates write HiLog terms
</div><div id="l483" class="code_block">    as Prolog terms.
</div><div id="l484" class="code_block">
</div><div id="l485" class="code_block"><span class="k">\ournewitem</span><span class="nb">{</span>write<span class="k">\_prolog</span>(+Stream,?Term)<span class="nb">}{</span>HiLog<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>write<span class="k">\_prolog</span>/2<span class="nb">}}</span>
</div><div id="l486" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> write<span class="k">\_prolog</span>/2<span class="nb">}</span> has the same behavior as <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l487" class="code_block">	write<span class="k">\_prolog</span>/1<span class="nb">}</span> but the output stream is explicitly
</div><div id="l488" class="code_block">	designated using the first argument.
</div><div id="l489" class="code_block">
</div><div id="l490" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>writeq(?Term)<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>writeq/1<span class="nb">}}</span>
</div><div id="l491" class="code_block">    Acts as <span class="nb">{</span><span class="k">\tt</span> write(Term)<span class="nb">}</span>, but atoms and functors are quoted
</div><div id="l492" class="code_block">    whenever necessary to make the result acceptable as input to 
</div><div id="l493" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> read/1<span class="nb">}</span><span class="k">\@</span>. <span class="nb">{</span><span class="k">\tt</span> writeq/1<span class="nb">}</span> treats treats terms of the form 
</div><div id="l494" class="code_block">    <span class="k">\verb</span>|&#39;<span class="k">\VAR</span>&#39;(N)| the same way as <span class="nb">{</span><span class="k">\tt</span> write/1<span class="nb">}</span>, writing <span class="nb">{</span><span class="k">\tt</span> A<span class="nb">}</span> if
</div><div id="l495" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> N<span class="nb">}</span>= 0, etc. 
</div><div id="l496" class="code_block"><span class="c">%% $</span>
</div><div id="l497" class="code_block">
</div><div id="l498" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> writeq/1<span class="nb">}</span> always succeeds without producing an error.
</div><div id="l499" class="code_block">
</div><div id="l500" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>writeq(+Stream, ?Term)<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>writeq/2<span class="nb">}}</span>
</div><div id="l501" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> writeq/2<span class="nb">}</span> has the same behavior as <span class="nb">{</span><span class="k">\tt</span> writeq/1<span class="nb">}</span> but the
</div><div id="l502" class="code_block">	output stream is explicitly designated using the first argument.
</div><div id="l503" class="code_block">
</div><div id="l504" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>write<span class="k">\_canonical</span>(?Term)<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\texttt</span><span class="nb">{</span>write<span class="k">\_canonical</span>/1<span class="nb">}}</span>
</div><div id="l505" class="code_block">    This predicate is provided so that the HiLog term <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span>, 
</div><div id="l506" class="code_block">    if written to a file, can be read back using <span class="nb">{</span><span class="k">\tt</span> read/1<span class="nb">}</span> regardless of 
</div><div id="l507" class="code_block">    special characters appearing in <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> or prevailing operator 
</div><div id="l508" class="code_block">    declarations. Like <span class="nb">{</span><span class="k">\tt</span> write<span class="k">\_prolog</span>/1<span class="nb">}</span>, <span class="nb">{</span><span class="k">\tt</span> write<span class="k">\_canonical</span>/1<span class="nb">}</span> 
</div><div id="l509" class="code_block">    writes all proper HiLog terms to the current output stream using the 
</div><div id="l510" class="code_block">    standard Prolog syntax (see Section~<span class="k">\ref</span><span class="nb">{</span>TermSyntax<span class="nb">}</span> on the standard 
</div><div id="l511" class="code_block">    syntax of HiLog terms). <span class="nb">{</span><span class="k">\tt</span> write<span class="k">\_canonical</span>/1<span class="nb">}</span> also quotes atoms and 
</div><div id="l512" class="code_block">    functors as <span class="nb">{</span><span class="k">\tt</span> writeq/1<span class="nb">}</span> does, to make them acceptable as input of 
</div><div id="l513" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> read/1<span class="nb">}</span><span class="k">\@</span>.  Operator declarations are not taken into consideration,
</div><div id="l514" class="code_block">    and compound terms are therefore always written in the form:
</div><div id="l515" class="code_block">
</div><div id="l516" class="code_block">		<span class="sb">\[</span><span class="nb"> </span><span class="nv">\langle</span><span class="nb"> predicate</span><span class="nv">\</span><span class="nb"> name </span><span class="nv">\rangle</span>
</div><div id="l517" class="code_block"><span class="nb">			</span><span class="o">(</span><span class="nv">\langle</span><span class="nb"> arg_</span><span class="m">1</span><span class="nb"> </span><span class="nv">\rangle</span><span class="nb">, </span><span class="nv">\ldots</span><span class="nb">,</span>
</div><div id="l518" class="code_block"><span class="nb">			 </span><span class="nv">\langle</span><span class="nb"> arg_n </span><span class="nv">\rangle</span><span class="o">)</span><span class="nb"> </span><span class="s">\]</span>
</div><div id="l519" class="code_block">
</div><div id="l520" class="code_block">    Unlike <span class="nb">{</span><span class="k">\tt</span> writeq/1<span class="nb">}</span>, <span class="nb">{</span><span class="k">\tt</span> write<span class="k">\_canonical</span>/1<span class="nb">}</span> does not treat terms 
</div><div id="l521" class="code_block">    of the form <span class="k">\verb</span>|&#39;<span class="s">$</span><span class="nb">VAR&#39;</span><span class="o">(</span><span class="nb">N</span><span class="o">)</span><span class="nb">| specially. It writes square bracket lists </span>
</div><div id="l522" class="code_block"><span class="nb">    using {</span><span class="nv">\tt</span><span class="nb"> &#39;.&#39;</span><span class="o">/</span><span class="m">2</span><span class="nb">} and {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">[]</span><span class="nb">} </span><span class="o">(</span><span class="nb">that is, {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">[</span><span class="nb">foo, bar</span><span class="o">]</span><span class="nb">} is written </span>
</div><div id="l523" class="code_block"><span class="nb">    as </span><span class="nv">\verb</span><span class="nb">|&#39;.&#39;</span><span class="o">(</span><span class="nb">foo,&#39;.&#39;</span><span class="o">(</span><span class="nb">bar,</span><span class="o">[]))</span><span class="nb">|</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l524" class="code_block"><span class="c">%% $</span>
</div><div id="l525" class="code_block">
</div><div id="l526" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{read</span><span class="nv">\_</span><span class="nb">canonical</span><span class="o">(-</span><span class="nb">Term</span><span class="o">)</span><span class="nb">}{basics} </span>
</div><div id="l527" class="code_block"><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{read</span><span class="nv">\_</span><span class="nb">canonical</span><span class="o">/</span><span class="m">1</span><span class="nb">}} </span>
</div><div id="l528" class="code_block"><span class="nb">Reads a term that is in canonical format from the</span>
</div><div id="l529" class="code_block"><span class="nb">current input stream and returns it in {</span><span class="nv">\tt</span><span class="nb"> Term}. On end</span><span class="o">-</span><span class="nb">of</span><span class="o">-</span><span class="nb">file, it</span>
</div><div id="l530" class="code_block"><span class="nb">returns the atom {</span><span class="nv">\tt</span><span class="nb"> end</span><span class="nv">\_</span><span class="nb">of</span><span class="nv">\_</span><span class="nb">file}.  If it encounters an error, it</span>
</div><div id="l531" class="code_block"><span class="nb">prints an error message on stderr and returns the atom {</span><span class="nv">\tt</span>
</div><div id="l532" class="code_block"><span class="nb">read</span><span class="nv">\_</span><span class="nb">canonical</span><span class="nv">\_</span><span class="nb">error}. This is significantly faster than {</span><span class="nv">\tt</span>
</div><div id="l533" class="code_block"><span class="nb">read</span><span class="o">/</span><span class="m">1</span><span class="nb">}, but requires the input to be in canonical form.</span>
</div><div id="l534" class="code_block">
</div><div id="l535" class="code_block"><span class="nv">\ouritem</span><span class="nb">{write</span><span class="nv">\_</span><span class="nb">canonical</span><span class="o">(+</span><span class="nb">Stream, ?Term</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{write</span><span class="nv">\_</span><span class="nb">canonical</span><span class="o">/</span><span class="m">2</span><span class="nb">}}</span>
</div><div id="l536" class="code_block"><span class="nb">	{</span><span class="nv">\tt</span><span class="nb"> write</span><span class="nv">\_</span><span class="nb">canonical</span><span class="o">/</span><span class="m">2</span><span class="nb">} has the same behavior as {</span><span class="nv">\tt</span>
</div><div id="l537" class="code_block"><span class="nb">	write</span><span class="nv">\_</span><span class="nb">canonical</span><span class="o">/</span><span class="m">1</span><span class="nb">} but the output stream is explicitly</span>
</div><div id="l538" class="code_block"><span class="nb">	designated using the first argument.</span>
</div><div id="l539" class="code_block">
</div><div id="l540" class="code_block"><span class="nv">\ouritem</span><span class="nb">{print</span><span class="o">(</span><span class="nb">?Term</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{print</span><span class="o">/</span><span class="m">1</span><span class="nb">}}</span>
</div><div id="l541" class="code_block"><span class="nb">    This predicate is intended to provide a handle for user</span><span class="o">-</span><span class="nb">defined </span>
</div><div id="l542" class="code_block"><span class="nb">    pretty</span><span class="o">-</span><span class="nb">printing.  Currently it is defined as {</span><span class="nv">\em</span><span class="nb"> write</span><span class="o">/</span><span class="m">1</span><span class="nb">}.</span>
</div><div id="l543" class="code_block">
</div><div id="l544" class="code_block"><span class="nv">\end</span><span class="nb">{description}</span>
</div><div id="l545" class="code_block">
</div><div id="l546" class="code_block"><span class="nv">\comment</span><span class="nb">{ TLS: Taken out because this appears to be superceded by</span>
</div><div id="l547" class="code_block"><span class="nb">documentation in Manual </span><span class="m">2</span>
</div><div id="l548" class="code_block">
</div><div id="l549" class="code_block"><span class="nv">\section</span><span class="nb">{Special I</span><span class="o">/</span><span class="nb">O}</span>
</div><div id="l550" class="code_block">
</div><div id="l551" class="code_block"><span class="nv">\begin</span><span class="nb">{description}</span>
</div><div id="l552" class="code_block"><span class="nv">\ouritem</span><span class="nb">{fmt</span><span class="nv">\_</span><span class="nb">read</span><span class="o">(+</span><span class="nb">Format, types</span><span class="o">(+</span><span class="nb">T</span><span class="m">1</span><span class="nb">,</span><span class="o">+</span><span class="nb">T</span><span class="m">2</span><span class="nb">,...</span><span class="o">)</span><span class="nb">, args</span><span class="o">(-</span><span class="nb">A</span><span class="m">1</span><span class="nb">,</span><span class="o">-</span><span class="nb">A</span><span class="m">2</span><span class="nb">,...</span><span class="o">)</span><span class="nb">, </span><span class="o">-</span><span class="nb">RetCode</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{fmt</span><span class="nv">\_</span><span class="nb">read</span><span class="o">/</span><span class="m">4</span><span class="nb">}} </span>
</div><div id="l553" class="code_block"><span class="nb"> This predicate implements C</span><span class="o">-</span><span class="nb">style formatted input. It reads the current</span>
</div><div id="l554" class="code_block"><span class="nb"> input according to the {</span><span class="nv">\tt</span><span class="nb"> Format} string.  {</span><span class="nv">\tt</span><span class="nb"> Format} has the</span>
</div><div id="l555" class="code_block"><span class="nb"> same syntax as the input format in C. The term {</span><span class="nv">\tt</span><span class="nb"> types</span><span class="o">(</span><span class="nb">...</span><span class="o">)</span><span class="nb">} lists the</span>
</div><div id="l556" class="code_block"><span class="nb"> types of the arguments; they must match the types specified in {</span><span class="nv">\tt</span>
</div><div id="l557" class="code_block"><span class="nb"> Format}. Here, </span><span class="m">1</span><span class="nb"> means string, </span><span class="m">2</span><span class="nb"> means integer, and </span><span class="m">3</span><span class="nb"> means float.</span>
</div><div id="l558" class="code_block"><span class="nb"> The term {</span><span class="nv">\tt</span><span class="nb"> args</span><span class="o">()</span><span class="nb">} specifies the variables for the input. {</span><span class="nv">\tt</span><span class="nb"> RetCode}</span>
</div><div id="l559" class="code_block"><span class="nb"> specifies the return code: </span><span class="m">0</span><span class="nb"> </span><span class="o">--</span><span class="nb"> ok; </span><span class="o">-</span><span class="m">1</span><span class="nb"> </span><span class="o">--</span><span class="nb"> end of file.</span>
</div><div id="l560" class="code_block">
</div><div id="l561" class="code_block"><span class="nv">\ouritem</span><span class="nb">{read</span><span class="nv">\_</span><span class="nb">line</span><span class="o">(-</span><span class="nb">Line, </span><span class="o">-</span><span class="nb">Status</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{read</span><span class="nv">\_</span><span class="nb">line</span><span class="o">/</span><span class="m">2</span><span class="nb">}} </span>
</div><div id="l562" class="code_block"><span class="nb"> Reads the next line from the current input and puts it in {</span><span class="nv">\tt</span><span class="nb"> Line}.</span>
</div><div id="l563" class="code_block"><span class="nb"> If the line is larger than the available buffer, then {</span><span class="nv">\tt</span><span class="nb"> Status} is </span><span class="m">0</span><span class="nb">.</span>
</div><div id="l564" class="code_block"><span class="nb"> If the line was read in full, up to and including the newline character,</span>
</div><div id="l565" class="code_block"><span class="nb"> then {</span><span class="nv">\tt</span><span class="nb"> Status} is </span><span class="m">1</span><span class="nb">. </span>
</div><div id="l566" class="code_block">
</div><div id="l567" class="code_block"><span class="nv">\ouritem</span><span class="nb">{fmt</span><span class="nv">\_</span><span class="nb">write</span><span class="o">(+</span><span class="nb">Format, args</span><span class="o">(-</span><span class="nb">A</span><span class="m">1</span><span class="nb">,</span><span class="o">-</span><span class="nb">A</span><span class="m">2</span><span class="nb">,...</span><span class="o">))</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{fmt</span><span class="nv">\_</span><span class="nb">write</span><span class="o">/</span><span class="m">2</span><span class="nb">}} </span>
</div><div id="l568" class="code_block"><span class="nb"> Similar to formatted write in C. The semantics of the arguments is the</span>
</div><div id="l569" class="code_block"><span class="nb"> same as for {</span><span class="nv">\tt</span><span class="nb"> fmt</span><span class="nv">\_</span><span class="nb">read</span><span class="o">/</span><span class="m">4</span><span class="nb">}.</span>
</div><div id="l570" class="code_block">
</div><div id="l571" class="code_block"><span class="nv">\ouritem</span><span class="nb">{fmt</span><span class="nv">\_</span><span class="nb">write</span><span class="nv">\_</span><span class="nb">string</span><span class="o">(-</span><span class="nb">String, </span><span class="o">+</span><span class="nb">Format, args</span><span class="o">(-</span><span class="nb">A</span><span class="m">1</span><span class="nb">,</span><span class="o">-</span><span class="nb">A</span><span class="m">2</span><span class="nb">,...</span><span class="o">))</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{fmt</span><span class="nv">\_</span><span class="nb">write</span><span class="o">/</span><span class="m">2</span><span class="nb">}} </span>
</div><div id="l572" class="code_block"><span class="nb"> Like {</span><span class="nv">\tt</span><span class="nb"> fmt</span><span class="nv">\_</span><span class="nb">write</span><span class="o">/</span><span class="m">2</span><span class="nb">}, but the output string is placed in {</span><span class="nv">\tt</span><span class="nb"> String}.</span>
</div><div id="l573" class="code_block">
</div><div id="l574" class="code_block"><span class="nv">\end</span><span class="nb">{description}</span>
</div><div id="l575" class="code_block"><span class="nb">}</span>
</div><div id="l576" class="code_block">
</div><div id="l577" class="code_block"><span class="nv">\section</span><span class="nb">{Evaluating Arithmetic Expressions through {</span><span class="nv">\tt</span><span class="nb"> is</span><span class="o">/</span><span class="m">2</span><span class="nb">}}</span>
</div><div id="l578" class="code_block"><span class="nv">\label</span><span class="nb">{Arithmetic} </span>
</div><div id="l579" class="code_block">
</div><div id="l580" class="code_block"><span class="nb">As do most Prologs, XSB supports evaluation of arithmetic expressions</span>
</div><div id="l581" class="code_block"><span class="nb">in two ways.  First, XSB supports evaluation of ground arithmetic</span>
</div><div id="l582" class="code_block"><span class="nb">expressions throught the {</span><span class="nv">\tt</span><span class="nb"> is</span><span class="o">/</span><span class="m">2</span><span class="nb">} operator.  Support of comparisons</span>
</div><div id="l583" class="code_block"><span class="nb">of non</span><span class="o">-</span><span class="nb">ground arithmetic expressions is provided through the port to</span>
</div><div id="l584" class="code_block"><span class="nb">XSB of the CLPQR constraint handling interface.  In this section we</span>
</div><div id="l585" class="code_block"><span class="nb">describe how arithmetic expressions can be evaluated through {</span><span class="nv">\tt</span>
</div><div id="l586" class="code_block"><span class="nb">is</span><span class="o">/</span><span class="m">2</span><span class="nb">}, while the CLPQR interface is described in Volume </span><span class="m">2</span><span class="nb"> of this</span>
</div><div id="l587" class="code_block"><span class="nb">manual.</span>
</div><div id="l588" class="code_block">
</div><div id="l589" class="code_block"><span class="nb">Before describing {</span><span class="nv">\tt</span><span class="nb"> is</span><span class="o">/</span><span class="m">2</span><span class="nb">} and the expressions that it can evaluate,</span>
</div><div id="l590" class="code_block"><span class="nb">we note that in </span><span class="nv">\version</span><span class="nb">{} of XSB, integers and floats in XSB are</span>
</div><div id="l591" class="code_block"><span class="nb">represented using a single word of </span><span class="m">32</span><span class="nb"> or </span><span class="m">64</span><span class="nb"> bits, depending on the</span>
</div><div id="l592" class="code_block"><span class="nb">machine architecture.  Since type tags constitute part of this word,</span>
</div><div id="l593" class="code_block"><span class="nb">this means that there may be as little as </span><span class="m">28</span><span class="nb"> bits available to</span>
</div><div id="l594" class="code_block"><span class="nb">represent a floating point number.  In addition, evaluation of</span>
</div><div id="l595" class="code_block"><span class="nb">arithmetic expressions through {</span><span class="nv">\tt</span><span class="nb"> is</span><span class="o">/</span><span class="m">2</span><span class="nb">} does not check for overflow</span>
</div><div id="l596" class="code_block"><span class="nb">or underflow.  As a result, XSB&#39;s floating point operations do not</span>
</div><div id="l597" class="code_block"><span class="nb">conform to IEEE floating point standards, and deviates in this regard</span>
</div><div id="l598" class="code_block"><span class="nb">from the ISO Prolog standard </span><span class="o">(</span><span class="nb">see </span><span class="nv">\cite</span><span class="nb">{ISO</span><span class="o">-</span><span class="nb">Prolog} Section </span><span class="m">9</span><span class="o">)</span><span class="nb">.  We</span>
</div><div id="l599" class="code_block"><span class="nb">hope to fix these problems in a future release </span><span class="nv">\footnote</span><span class="nb">{We also note</span>
</div><div id="l600" class="code_block"><span class="nb">that the ISO Prolog evaluable functors {</span><span class="nv">\tt</span><span class="nb"> sign</span><span class="o">/</span><span class="m">1</span><span class="nb">}, {</span><span class="nv">\tt</span>
</div><div id="l601" class="code_block"><span class="nb">float</span><span class="nv">\_</span><span class="nb">round</span><span class="o">/</span><span class="m">1</span><span class="nb">}, {</span><span class="nv">\tt</span><span class="nb"> float</span><span class="nv">\_</span><span class="nb">truncate</span><span class="o">/</span><span class="m">1</span><span class="nb">}, {</span><span class="nv">\tt</span><span class="nb"> float</span><span class="nv">\_</span><span class="nb">integer</span><span class="nv">\_</span><span class="nb">part</span><span class="o">/</span><span class="m">1</span><span class="nb">}</span>
</div><div id="l602" class="code_block"><span class="nb">and {</span><span class="nv">\tt</span><span class="nb"> float</span><span class="nv">\_</span><span class="nb">fractional</span><span class="nv">\_</span><span class="nb">part</span><span class="o">/</span><span class="m">1</span><span class="nb">} are not implemented in </span><span class="nv">\version</span><span class="nb"> .}</span>
</div><div id="l603" class="code_block">
</div><div id="l604" class="code_block"><span class="nb">All of the evaluable functors describe below throw a type error if</span>
</div><div id="l605" class="code_block"><span class="nb">their evaluated input is not numeric.  We describe below only their</span>
</div><div id="l606" class="code_block"><span class="nb">behavior on correctly typed input.</span>
</div><div id="l607" class="code_block">
</div><div id="l608" class="code_block"><span class="nv">\begin</span><span class="nb">{description}</span>
</div><div id="l609" class="code_block"><span class="nv">\ouritem</span><span class="nb">{is</span><span class="o">(</span><span class="nb">?Result,</span><span class="o">+</span><span class="nb">Expression</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{is</span><span class="o">/</span><span class="m">2</span><span class="nb">}} </span>
</div><div id="l610" class="code_block"><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> is</span><span class="o">(</span><span class="nb">Result,Expression</span><span class="o">)</span><span class="nb">} is true iff the result of evaluating {</span><span class="nv">\tt</span>
</div><div id="l611" class="code_block"><span class="nb">Expression} as a sequence of evaluable functors unifies with {</span><span class="nv">\tt</span>
</div><div id="l612" class="code_block"><span class="nb">Result}.  As mentioned in Section~</span><span class="nv">\ref</span><span class="nb">{inline_predicates}, {</span><span class="nv">\tt</span><span class="nb"> is</span><span class="o">/</span><span class="m">2</span><span class="nb">}</span>
</div><div id="l613" class="code_block"><span class="nb">is an inline predicate, so calls to {</span><span class="nv">\tt</span><span class="nb"> is</span><span class="o">/</span><span class="m">2</span><span class="nb">} within compiled code</span>
</div><div id="l614" class="code_block"><span class="nb">will not be visible during a trace of program execution.</span>
</div><div id="l615" class="code_block"><span class="nv">\end</span><span class="nb">{description}</span>
</div><div id="l616" class="code_block">
</div><div id="l617" class="code_block"><span class="nv">\subsection</span><span class="nb">{Evaluable Functors for Arithmetic Expressions}</span>
</div><div id="l618" class="code_block">
</div><div id="l619" class="code_block"><span class="nv">\begin</span><span class="nb">{description}</span>
</div><div id="l620" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{</span><span class="o">+(+</span><span class="nb">Expr</span><span class="m">1</span><span class="nb">,</span><span class="o">+</span><span class="nb">Expr</span><span class="m">2</span><span class="o">)</span><span class="nb">}{Evaluable Functor}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{</span><span class="o">+/</span><span class="m">2</span><span class="nb">}} </span>
</div><div id="l621" class="code_block"><span class="nb">If {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">+</span><span class="nb">Expr</span><span class="m">1</span><span class="nb">} evaluates to {</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">1</span><span class="nb">}, and {</span><span class="nv">\tt</span><span class="nb"> Expr</span><span class="m">2</span><span class="nb">} evaluates</span>
</div><div id="l622" class="code_block"><span class="nb">to {</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">2</span><span class="nb">}, returns {</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">1</span><span class="nb"> </span><span class="o">+</span><span class="nb"> Number</span><span class="m">2</span><span class="nb">}, performing any</span>
</div><div id="l623" class="code_block"><span class="nb">necessary type conversions.</span>
</div><div id="l624" class="code_block">
</div><div id="l625" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{</span><span class="o">-(+</span><span class="nb">Expr</span><span class="m">1</span><span class="nb">,</span><span class="o">+</span><span class="nb">Expr</span><span class="m">2</span><span class="o">)</span><span class="nb">}{Evaluable Functor}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{</span><span class="o">-/</span><span class="m">2</span><span class="nb">}} </span>
</div><div id="l626" class="code_block"><span class="nb">If {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">+</span><span class="nb">Expr</span><span class="m">1</span><span class="nb">} evaluates to {</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">1</span><span class="nb">}, and {</span><span class="nv">\tt</span><span class="nb"> Expr</span><span class="m">2</span><span class="nb">} evaluates</span>
</div><div id="l627" class="code_block"><span class="nb">to {</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">2</span><span class="nb">}, returns {</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">1</span><span class="nb"> </span><span class="o">-</span><span class="nb"> Number</span><span class="m">2</span><span class="nb">}, performing any</span>
</div><div id="l628" class="code_block"><span class="nb">necessary type conversions.</span>
</div><div id="l629" class="code_block">
</div><div id="l630" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{</span><span class="o">*(+</span><span class="nb">Expr</span><span class="m">1</span><span class="nb">,</span><span class="o">+</span><span class="nb">Expr</span><span class="m">2</span><span class="o">)</span><span class="nb">}{Evaluable Functor}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{</span><span class="o">*/</span><span class="m">2</span><span class="nb">}} </span>
</div><div id="l631" class="code_block"><span class="nb">If {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">+</span><span class="nb">Expr</span><span class="m">1</span><span class="nb">} evaluates to {</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">1</span><span class="nb">}, and {</span><span class="nv">\tt</span><span class="nb"> Expr</span><span class="m">2</span><span class="nb">} evaluates</span>
</div><div id="l632" class="code_block"><span class="nb">to {</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">2</span><span class="nb">}, returns {</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">1</span><span class="nb"> </span><span class="o">*</span><span class="nb"> Number</span><span class="m">2</span><span class="nb">} </span><span class="o">(</span><span class="nb">i.e. multiplies</span>
</div><div id="l633" class="code_block"><span class="nb">them</span><span class="o">)</span><span class="nb">, performing any necessary type conversions.</span>
</div><div id="l634" class="code_block">
</div><div id="l635" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{</span><span class="o">/(+</span><span class="nb">Expr</span><span class="m">1</span><span class="nb">,Expr</span><span class="m">2</span><span class="o">)</span><span class="nb">}{Evaluable Functor}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{&#39;</span><span class="o">/</span><span class="nb">&#39;</span><span class="o">/</span><span class="m">2</span><span class="nb">}}</span>
</div><div id="l636" class="code_block"><span class="nb">If {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">+</span><span class="nb">Expr</span><span class="m">1</span><span class="nb">} evaluates to {</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">1</span><span class="nb">}, and {</span><span class="nv">\tt</span><span class="nb"> Expr</span><span class="m">2</span><span class="nb">} evaluates</span>
</div><div id="l637" class="code_block"><span class="nb">to {</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">2</span><span class="nb">}, returns {</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">1</span><span class="nb"> </span><span class="o">/</span><span class="nb"> Number</span><span class="m">2</span><span class="nb">} </span><span class="o">(</span><span class="nb">i.e. divides</span>
</div><div id="l638" class="code_block"><span class="nb">them</span><span class="o">)</span><span class="nb">, performing any necessary type conversions.</span>
</div><div id="l639" class="code_block">
</div><div id="l640" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{</span><span class="o">//(+</span><span class="nb">Expr</span><span class="m">1</span><span class="nb">,Expr</span><span class="m">2</span><span class="o">)</span><span class="nb">}{Evaluable Functor}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{&#39;</span><span class="o">//</span><span class="nb">&#39;</span><span class="o">/</span><span class="m">2</span><span class="nb">}}</span>
</div><div id="l641" class="code_block"><span class="nb">If {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">+</span><span class="nb">Expr</span><span class="m">1</span><span class="nb">} evaluates to {</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">1</span><span class="nb">}, and {</span><span class="nv">\tt</span><span class="nb"> Expr</span><span class="m">2</span><span class="nb">} evaluates</span>
</div><div id="l642" class="code_block"><span class="nb">to {</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">2</span><span class="nb">}, returns {</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">1</span><span class="nb"> </span><span class="o">//</span><span class="nb"> Number</span><span class="m">2</span><span class="nb">} </span><span class="o">(</span><span class="nb">i.e. integer</span>
</div><div id="l643" class="code_block"><span class="nb">division</span><span class="o">)</span><span class="nb">, performing any necessary type conversions, and rounding to</span>
</div><div id="l644" class="code_block"><span class="m">0</span><span class="nb"> if necessary.  </span>
</div><div id="l645" class="code_block">
</div><div id="l646" class="code_block"><span class="nb">    Example:</span>
</div><div id="l647" class="code_block"><span class="nb">    {</span><span class="nv">\footnotesize</span>
</div><div id="l648" class="code_block"><span class="nb">     </span><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l649" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> X is </span><span class="m">3</span><span class="o">/</span><span class="m">2</span><span class="nb">.</span>
</div><div id="l650" class="code_block">
</div><div id="l651" class="code_block"><span class="nb">                X </span><span class="o">=</span><span class="nb"> </span><span class="m">1</span><span class="nb">.</span><span class="m">5000</span>
</div><div id="l652" class="code_block">
</div><div id="l653" class="code_block"><span class="nb">                yes</span>
</div><div id="l654" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> X is </span><span class="m">3</span><span class="nb"> </span><span class="o">//</span><span class="nb"> </span><span class="m">2</span><span class="nb">.</span>
</div><div id="l655" class="code_block">
</div><div id="l656" class="code_block"><span class="nb">                X </span><span class="o">=</span><span class="nb"> </span><span class="m">1</span>
</div><div id="l657" class="code_block">
</div><div id="l658" class="code_block"><span class="nb">                yes</span>
</div><div id="l659" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> X is </span><span class="o">-</span><span class="m">3</span><span class="nb"> </span><span class="o">//</span><span class="nb"> </span><span class="m">2</span><span class="nb">.</span>
</div><div id="l660" class="code_block">
</div><div id="l661" class="code_block"><span class="nb">                X </span><span class="o">=</span><span class="nb"> </span><span class="o">-</span><span class="m">1</span>
</div><div id="l662" class="code_block">
</div><div id="l663" class="code_block"><span class="nb">                yes</span>
</div><div id="l664" class="code_block"><span class="nb">  </span><span class="nv">\end</span><span class="nb">{verbatim}}</span>
</div><div id="l665" class="code_block">
</div><div id="l666" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{</span><span class="o">-(+</span><span class="nb">Expr</span><span class="m">1</span><span class="o">)</span><span class="nb">}{Evaluable Functor}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{</span><span class="o">-/</span><span class="m">1</span><span class="nb">}} If {</span><span class="nv">\tt</span>
</div><div id="l667" class="code_block"><span class="o">+</span><span class="nb">Expr} evaluates to {</span><span class="nv">\tt</span><span class="nb"> Number}, returns {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">-</span><span class="nb">Number</span><span class="m">1</span><span class="nb">},</span>
</div><div id="l668" class="code_block"><span class="nb">performing any necessary type conversions.</span>
</div><div id="l669" class="code_block">
</div><div id="l670" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{&#39;</span><span class="o">/</span><span class="nv">\&#39;</span><span class="o">(+</span><span class="nb">Expr</span><span class="m">1</span><span class="nb">,</span><span class="o">+</span><span class="nb">Expr</span><span class="m">2</span><span class="o">)</span><span class="nb">}{Evaluable Functor}</span>
</div><div id="l671" class="code_block"><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{&#39;</span><span class="o">/</span><span class="nv">\&#39;</span><span class="o">/</span><span class="m">2</span><span class="nb">}} If {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">+</span><span class="nb">Expr</span><span class="m">1</span><span class="nb">} evaluates to {</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">1</span><span class="nb">}, and {</span><span class="nv">\tt</span><span class="nb"> Expr</span><span class="m">2</span><span class="nb">}</span>
</div><div id="l672" class="code_block"><span class="nb">evaluates to {</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">2</span><span class="nb">}, returns the bitwise conjunction of {</span><span class="nv">\tt</span>
</div><div id="l673" class="code_block"><span class="nb">Number</span><span class="m">1</span><span class="nb">} and {</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">2</span><span class="nb">}.</span>
</div><div id="l674" class="code_block">
</div><div id="l675" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{&#39;</span><span class="nv">\/</span><span class="nb">&#39;</span><span class="o">(+</span><span class="nb">Expr</span><span class="m">1</span><span class="nb">,</span><span class="o">+</span><span class="nb">Expr</span><span class="m">2</span><span class="o">)</span><span class="nb">}{Evaluable Functor}</span>
</div><div id="l676" class="code_block"><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{&#39;</span><span class="nv">\/</span><span class="nb">&#39;</span><span class="o">/</span><span class="m">2</span><span class="nb">}} If {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">+</span><span class="nb">Expr</span><span class="m">1</span><span class="nb">} evaluates to {</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">1</span><span class="nb">}, and {</span><span class="nv">\tt</span><span class="nb"> Expr</span><span class="m">2</span><span class="nb">}</span>
</div><div id="l677" class="code_block"><span class="nb">evaluates to {</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">2</span><span class="nb">}, returns the bitwise disjunction {</span><span class="nv">\tt</span>
</div><div id="l678" class="code_block"><span class="nb">Number</span><span class="m">1</span><span class="nb">} and {</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">2</span><span class="nb">}.</span>
</div><div id="l679" class="code_block">
</div><div id="l680" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{&#39;&gt;&gt;&#39;</span><span class="o">(+</span><span class="nb">Expr</span><span class="m">1</span><span class="nb">,</span><span class="o">+</span><span class="nb">Expr</span><span class="m">2</span><span class="o">)</span><span class="nb">}{Evaluable Functor}</span>
</div><div id="l681" class="code_block"><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{&#39;&gt;&gt;&#39;</span><span class="o">/</span><span class="m">2</span><span class="nb">}} If {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">+</span><span class="nb">Expr</span><span class="m">1</span><span class="nb">} evaluates to {</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">1</span><span class="nb">}, and {</span><span class="nv">\tt</span><span class="nb"> Expr</span><span class="m">2</span><span class="nb">}</span>
</div><div id="l682" class="code_block"><span class="nb">evaluates to {</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">2</span><span class="nb">}, returns the logical shift right of </span>
</div><div id="l683" class="code_block"><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">1</span><span class="nb">}, {</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">2</span><span class="nb">} places.</span>
</div><div id="l684" class="code_block">
</div><div id="l685" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{&#39;&lt;&lt;&#39;</span><span class="o">(+</span><span class="nb">Expr</span><span class="m">1</span><span class="nb">,</span><span class="o">+</span><span class="nb">Expr</span><span class="m">2</span><span class="o">)</span><span class="nb">}{Evaluable Functor}</span>
</div><div id="l686" class="code_block"><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{&#39;&gt;&gt;&#39;</span><span class="o">/</span><span class="m">2</span><span class="nb">}} If {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">+</span><span class="nb">Expr</span><span class="m">1</span><span class="nb">} evaluates to {</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">1</span><span class="nb">}, and {</span><span class="nv">\tt</span><span class="nb"> Expr</span><span class="m">2</span><span class="nb">}</span>
</div><div id="l687" class="code_block"><span class="nb">evaluates to {</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">2</span><span class="nb">}, returns the logical shift left of </span>
</div><div id="l688" class="code_block"><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">1</span><span class="nb">}, {</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">2</span><span class="nb">} places.</span>
</div><div id="l689" class="code_block">
</div><div id="l690" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{ceiling</span><span class="o">(+</span><span class="nb">Expr</span><span class="o">)</span><span class="nb">}{Evaluable Functor}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{ceiling</span><span class="o">/</span><span class="m">1</span><span class="nb">}}</span>
</div><div id="l691" class="code_block"><span class="nb">If {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">+</span><span class="nb">Expr} evaluates to {</span><span class="nv">\tt</span><span class="nb"> Number}, {</span><span class="nv">\tt</span><span class="nb"> ceiling</span><span class="o">(</span><span class="nb">Number</span><span class="o">)</span><span class="nb">}</span>
</div><div id="l692" class="code_block"><span class="nb">returns the integer ceiling of {</span><span class="nv">\tt</span><span class="nb"> Number} if {</span><span class="nv">\tt</span><span class="nb"> Number} is a</span>
</div><div id="l693" class="code_block"><span class="nb">float, and {</span><span class="nv">\tt</span><span class="nb"> Number} itself if {</span><span class="nv">\tt</span><span class="nb"> Number} is an integer.</span>
</div><div id="l694" class="code_block">
</div><div id="l695" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{float</span><span class="o">(+</span><span class="nb">Expr</span><span class="o">)</span><span class="nb">}{Evaluable Functor}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{float</span><span class="o">/</span><span class="m">1</span><span class="nb">}} If</span>
</div><div id="l696" class="code_block"><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">+</span><span class="nb">Expr} evaluates to {</span><span class="nv">\tt</span><span class="nb"> Number}, {</span><span class="nv">\tt</span><span class="nb"> float</span><span class="o">(</span><span class="nb">Number</span><span class="o">)</span><span class="nb">} converts </span>
</div><div id="l697" class="code_block"><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> Number} to a float if {</span><span class="nv">\tt</span><span class="nb"> Number} is an integer, and returns {</span><span class="nv">\tt</span>
</div><div id="l698" class="code_block"><span class="nb">Number} itself if {</span><span class="nv">\tt</span><span class="nb"> Number} is a float.</span>
</div><div id="l699" class="code_block">
</div><div id="l700" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{floor</span><span class="o">(+</span><span class="nb">Expr</span><span class="o">)</span><span class="nb">}{Evaluable Functor}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{floor</span><span class="o">/</span><span class="m">1</span><span class="nb">}} If</span>
</div><div id="l701" class="code_block"><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">+</span><span class="nb">Expr} evaluates to {</span><span class="nv">\tt</span><span class="nb"> Number}, {</span><span class="nv">\tt</span><span class="nb"> floor</span><span class="o">(</span><span class="nb">Number</span><span class="o">)</span><span class="nb">} returns the</span>
</div><div id="l702" class="code_block"><span class="nb">integer floor of {</span><span class="nv">\tt</span><span class="nb"> Number} if {</span><span class="nv">\tt</span><span class="nb"> Number} is a float, and {</span><span class="nv">\tt</span>
</div><div id="l703" class="code_block"><span class="nb">Number} itself if {</span><span class="nv">\tt</span><span class="nb"> Number} is an integer.</span>
</div><div id="l704" class="code_block">
</div><div id="l705" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{mod</span><span class="o">(+</span><span class="nb">Expr</span><span class="m">1</span><span class="nb">,</span><span class="o">+</span><span class="nb">Expr</span><span class="m">2</span><span class="o">)</span><span class="nb">}{Evaluable Functor}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{mod</span><span class="o">/</span><span class="m">2</span><span class="nb">}}</span>
</div><div id="l706" class="code_block"><span class="nb">If {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">+</span><span class="nb">Expr</span><span class="m">1</span><span class="nb">} evaluates to {</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">1</span><span class="nb">} and {</span><span class="nv">\tt</span><span class="nb"> Expr</span><span class="m">2</span><span class="nb">} evaluates</span>
</div><div id="l707" class="code_block"><span class="nb">to {</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">2</span><span class="nb">} where {</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">2</span><span class="nb">} is not </span><span class="m">0</span><span class="nb">, {</span><span class="nv">\tt</span>
</div><div id="l708" class="code_block"><span class="nb">mod</span><span class="o">(</span><span class="nb">Number</span><span class="m">1</span><span class="nb">,Number</span><span class="m">2</span><span class="o">)</span><span class="nb">} returns</span>
</div><div id="l709" class="code_block"><span class="nv">\[</span>
</div><div id="l710" class="code_block"><span class="nb">	Number</span><span class="m">1</span><span class="nb"> </span><span class="o">-</span><span class="nb"> </span><span class="o">(</span><span class="nv">\lfloor</span><span class="nb"> </span><span class="o">(</span><span class="nb">Number</span><span class="m">1</span><span class="nb"> </span><span class="o">/</span><span class="nb"> Number</span><span class="m">2</span><span class="o">)</span><span class="nb"> </span><span class="nv">\rfloor</span><span class="o">)</span><span class="nb"> </span><span class="nv">\times</span><span class="nb"> Number</span><span class="m">2</span><span class="o">)</span>
</div><div id="l711" class="code_block"><span class="nv">\]</span>
</div><div id="l712" class="code_block">
</div><div id="l713" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{rem</span><span class="o">(+</span><span class="nb">Expr</span><span class="m">1</span><span class="nb">,</span><span class="o">+</span><span class="nb">Expr</span><span class="m">2</span><span class="o">)</span><span class="nb">}{Evaluable Functor}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{rem</span><span class="o">/</span><span class="m">2</span><span class="nb">}}</span>
</div><div id="l714" class="code_block"><span class="nb">If {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">+</span><span class="nb">Expr</span><span class="m">1</span><span class="nb">} evaluates to {</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">1</span><span class="nb">} and {</span><span class="nv">\tt</span><span class="nb"> Expr</span><span class="m">2</span><span class="nb">} evaluates</span>
</div><div id="l715" class="code_block"><span class="nb">to {</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">2</span><span class="nb">} where {</span><span class="nv">\tt</span><span class="nb"> Number</span><span class="m">2</span><span class="nb">} is not </span><span class="m">0</span><span class="nb">, {</span><span class="nv">\tt</span>
</div><div id="l716" class="code_block"><span class="nb">rem</span><span class="o">(</span><span class="nb">Number</span><span class="m">1</span><span class="nb">,Number</span><span class="m">2</span><span class="o">)</span><span class="nb">} returns</span>
</div><div id="l717" class="code_block"><span class="nv">\[</span>
</div><div id="l718" class="code_block"><span class="nb">	Number</span><span class="m">1</span><span class="nb"> </span><span class="o">-</span><span class="nb"> </span><span class="o">(</span><span class="nb">{Number</span><span class="m">1</span><span class="nb">} </span><span class="o">//</span><span class="nb"> {Number</span><span class="m">2</span><span class="nb">}</span><span class="o">)</span><span class="nb"> </span><span class="nv">\times</span><span class="nb"> Number</span><span class="m">2</span><span class="o">)</span>
</div><div id="l719" class="code_block"><span class="nv">\]</span>
</div><div id="l720" class="code_block">
</div><div id="l721" class="code_block"><span class="nb">    Example:</span>
</div><div id="l722" class="code_block"><span class="nb">    {</span><span class="nv">\footnotesize</span>
</div><div id="l723" class="code_block"><span class="nb">     </span><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l724" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> X is </span><span class="m">5</span><span class="nb"> mod </span><span class="m">2</span><span class="nb">.</span>
</div><div id="l725" class="code_block">
</div><div id="l726" class="code_block"><span class="nb">                X </span><span class="o">=</span><span class="nb"> </span><span class="m">1</span>
</div><div id="l727" class="code_block">
</div><div id="l728" class="code_block"><span class="nb">                yes</span>
</div><div id="l729" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> X is </span><span class="m">5</span><span class="nb"> rem </span><span class="m">2</span><span class="nb">.</span>
</div><div id="l730" class="code_block">
</div><div id="l731" class="code_block"><span class="nb">                X </span><span class="o">=</span><span class="nb"> </span><span class="m">1</span>
</div><div id="l732" class="code_block">
</div><div id="l733" class="code_block"><span class="nb">                yes</span>
</div><div id="l734" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> X is </span><span class="m">5</span><span class="nb"> mod </span><span class="o">-</span><span class="m">2</span><span class="nb">.</span>
</div><div id="l735" class="code_block">
</div><div id="l736" class="code_block"><span class="nb">                X </span><span class="o">=</span><span class="nb"> </span><span class="o">-</span><span class="m">1</span>
</div><div id="l737" class="code_block">
</div><div id="l738" class="code_block"><span class="nb">                yes</span>
</div><div id="l739" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> X is </span><span class="m">5</span><span class="nb"> rem </span><span class="o">-</span><span class="m">2</span><span class="nb">.</span>
</div><div id="l740" class="code_block">
</div><div id="l741" class="code_block"><span class="nb">                X </span><span class="o">=</span><span class="nb"> </span><span class="m">1</span>
</div><div id="l742" class="code_block">
</div><div id="l743" class="code_block"><span class="nb">                yes</span>
</div><div id="l744" class="code_block"><span class="nb">  </span><span class="nv">\end</span><span class="nb">{verbatim}}</span>
</div><div id="l745" class="code_block">
</div><div id="l746" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{round</span><span class="o">(+</span><span class="nb">Expr</span><span class="o">)</span><span class="nb">}{Evaluable Functor}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{round</span><span class="o">/</span><span class="m">1</span><span class="nb">}} If</span>
</div><div id="l747" class="code_block"><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">+</span><span class="nb">Expr} evaluates to {</span><span class="nv">\tt</span><span class="nb"> Number}, {</span><span class="nv">\tt</span><span class="nb"> round</span><span class="o">(</span><span class="nb">Number</span><span class="o">)</span><span class="nb">} returns the</span>
</div><div id="l748" class="code_block"><span class="nb">nearest integer to {</span><span class="nv">\tt</span><span class="nb"> Number} if {</span><span class="nv">\tt</span><span class="nb"> Number} is a float, and {</span><span class="nv">\tt</span>
</div><div id="l749" class="code_block"><span class="nb">Number} itself if {</span><span class="nv">\tt</span><span class="nb"> Number} is an integer.</span>
</div><div id="l750" class="code_block">
</div><div id="l751" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{sqrt</span><span class="o">(+</span><span class="nb">Expr</span><span class="o">)</span><span class="nb">}{Evaluable Functor}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{sqrt</span><span class="o">/</span><span class="m">1</span><span class="nb">}}</span>
</div><div id="l752" class="code_block"><span class="nb">If {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">+</span><span class="nb">Expr} evaluates to {</span><span class="nv">\tt</span><span class="nb"> Number}, {</span><span class="nv">\tt</span><span class="nb"> sqrt</span><span class="o">(</span><span class="nb">Number</span><span class="o">)</span><span class="nb">}</span>
</div><div id="l753" class="code_block"><span class="nb">returns the square root of {</span><span class="nv">\tt</span><span class="nb"> Number}.</span>
</div><div id="l754" class="code_block">
</div><div id="l755" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{truncate</span><span class="o">(+</span><span class="nb">Expr</span><span class="o">)</span><span class="nb">}{Evaluable Functor}</span>
</div><div id="l756" class="code_block"><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{truncate</span><span class="o">/</span><span class="m">1</span><span class="nb">}} If {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">+</span><span class="nb">Expr} evaluates to {</span><span class="nv">\tt</span><span class="nb"> Number}, {</span><span class="nv">\tt</span>
</div><div id="l757" class="code_block"><span class="nb">truncate</span><span class="o">(</span><span class="nb">Number</span><span class="o">)</span><span class="nb">} truncates {</span><span class="nv">\tt</span><span class="nb"> Number} if {</span><span class="nv">\tt</span><span class="nb"> Number} is a float,</span>
</div><div id="l758" class="code_block"><span class="nb">and returns {</span><span class="nv">\tt</span><span class="nb"> Number} itself if {</span><span class="nv">\tt</span><span class="nb"> Number} is an integer.</span>
</div><div id="l759" class="code_block"><span class="nv">\end</span><span class="nb">{description}</span>
</div><div id="l760" class="code_block">
</div><div id="l761" class="code_block"><span class="nv">\subsubsection</span><span class="nb">{Mathematical Functions from {</span><span class="nv">\tt</span><span class="nb"> math.h}}</span>
</div><div id="l762" class="code_block"><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{cos</span><span class="o">/</span><span class="m">1</span><span class="nb">}} </span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{sin</span><span class="o">/</span><span class="m">1</span><span class="nb">}} </span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{tan</span><span class="o">/</span><span class="m">1</span><span class="nb">}}</span>
</div><div id="l763" class="code_block"><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{acos</span><span class="o">/</span><span class="m">1</span><span class="nb">}} </span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{asin</span><span class="o">/</span><span class="m">1</span><span class="nb">}} </span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{atan</span><span class="o">/</span><span class="m">1</span><span class="nb">}}</span>
</div><div id="l764" class="code_block"><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{log</span><span class="o">/</span><span class="m">1</span><span class="nb">}} </span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{log</span><span class="m">10</span><span class="o">/</span><span class="m">1</span><span class="nb">}}</span>
</div><div id="l765" class="code_block">
</div><div id="l766" class="code_block"><span class="nb">XSB also allows as evaluable functors, many of the functions form the</span>
</div><div id="l767" class="code_block"><span class="nb">C library {</span><span class="nv">\tt</span><span class="nb"> math.h}.  Functions included in XSB </span><span class="nv">\version</span><span class="nb">{} are {</span><span class="nv">\tt</span>
</div><div id="l768" class="code_block"><span class="nb">cos</span><span class="o">/</span><span class="m">1</span><span class="nb">}, {</span><span class="nv">\tt</span><span class="nb"> sin</span><span class="o">/</span><span class="m">1</span><span class="nb">}, {</span><span class="nv">\tt</span><span class="nb"> tan</span><span class="o">/</span><span class="m">1</span><span class="nb">}, {</span><span class="nv">\tt</span><span class="nb"> acos</span><span class="o">/</span><span class="m">1</span><span class="nb">}, {</span><span class="nv">\tt</span><span class="nb"> asin</span><span class="o">/</span><span class="m">1</span><span class="nb">}, {</span><span class="nv">\tt</span>
</div><div id="l769" class="code_block"><span class="nb">atan</span><span class="o">/</span><span class="m">1</span><span class="nb">}. {</span><span class="nv">\tt</span><span class="nb"> log</span><span class="o">/</span><span class="m">1</span><span class="nb">}, and {</span><span class="nv">\tt</span><span class="nb"> log</span><span class="m">10</span><span class="o">/</span><span class="m">1</span><span class="nb">}.  For their semantics, see</span>
</div><div id="l770" class="code_block"><span class="nb">documentation to {</span><span class="nv">\tt</span><span class="nb"> math.h}.</span>
</div><div id="l771" class="code_block">
</div><div id="l772" class="code_block"><span class="nv">\section</span><span class="nb">{Convenience} </span><span class="nv">\label</span><span class="nb">{Convenience}</span>
</div><div id="l773" class="code_block"><span class="nb">These predicates are standard and often self</span><span class="o">-</span><span class="nb">explanatory, so they are </span>
</div><div id="l774" class="code_block"><span class="nb">described only briefly.</span>
</div><div id="l775" class="code_block"><span class="nv">\begin</span><span class="nb">{description}</span>
</div><div id="l776" class="code_block">
</div><div id="l777" class="code_block"><span class="nv">\ouritem</span><span class="nb">{true}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{true</span><span class="o">/</span><span class="m">0</span><span class="nb">}} </span>
</div><div id="l778" class="code_block"><span class="c">%\predindex{true/0~(I)}</span>
</div><div id="l779" class="code_block"><span class="nb">    Always succeeds.</span>
</div><div id="l780" class="code_block">
</div><div id="l781" class="code_block"><span class="nv">\ouritem</span><span class="nb">{otherwise}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{otherwise</span><span class="o">/</span><span class="m">0</span><span class="nb">}} </span>
</div><div id="l782" class="code_block"><span class="c">%\predindex{otherwise/0~(B)}</span>
</div><div id="l783" class="code_block"><span class="nb">    Same as {</span><span class="nv">\tt</span><span class="nb"> true</span><span class="o">/</span><span class="m">0</span><span class="nb">}.</span>
</div><div id="l784" class="code_block">
</div><div id="l785" class="code_block"><span class="nv">\ouritem</span><span class="nb">{fail}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{fail</span><span class="o">/</span><span class="m">0</span><span class="nb">}}</span>
</div><div id="l786" class="code_block"><span class="c">%\predindex{fail/0~(I)}</span>
</div><div id="l787" class="code_block"><span class="nb">    Always fails.</span>
</div><div id="l788" class="code_block">
</div><div id="l789" class="code_block"><span class="nv">\ouritem</span><span class="nb">{X </span><span class="o">=</span><span class="nb"> Y}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{</span><span class="o">=/</span><span class="m">2</span><span class="nb">}} </span>
</div><div id="l790" class="code_block"><span class="c">%\predindex{=/2~(I)}</span>
</div><div id="l791" class="code_block"><span class="nb">    Defined as if by the clause ``Z</span><span class="o">=</span><span class="nb">Z&#39;&#39;, i.e.~{</span><span class="nv">\tt</span><span class="nb"> X} and~{</span><span class="nv">\tt</span><span class="nb"> Y} are unified.</span>
</div><div id="l792" class="code_block">
</div><div id="l793" class="code_block"><span class="nv">\ouritem</span><span class="nb">{X </span><span class="s">$</span><span class="k">\backslash</span><span class="s">$</span><span class="nv">\,</span><span class="o">=</span><span class="nb"> Y}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{</span><span class="s">$</span><span class="k">\backslash</span><span class="s">$</span><span class="o">=/</span><span class="m">2</span><span class="nb">}}</span>
</div><div id="l794" class="code_block"><span class="nb">    Succeeds if~{</span><span class="nv">\tt</span><span class="nb"> X} and~{</span><span class="nv">\tt</span><span class="nb"> Y} are not unifiable,</span>
</div><div id="l795" class="code_block"><span class="nb">    fails if~{</span><span class="nv">\tt</span><span class="nb"> X} and~{</span><span class="nv">\tt</span><span class="nb"> Y} are unifiable.</span>
</div><div id="l796" class="code_block"><span class="nb">    It is thus equivalent to {</span><span class="nv">\tt</span><span class="nb"> </span><span class="s">$</span><span class="k">\backslash</span><span class="s">$</span><span class="o">+</span><span class="nb">}</span><span class="nv">\/</span><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">(</span><span class="nb">X </span><span class="o">=</span><span class="nb"> Y</span><span class="o">)</span><span class="nb">}.</span>
</div><div id="l797" class="code_block"><span class="nv">\end</span><span class="nb">{description}</span>
</div><div id="l798" class="code_block">
</div><div id="l799" class="code_block">
</div><div id="l800" class="code_block"><span class="nv">\section</span><span class="nb">{Negation and Control}</span><span class="nv">\label</span><span class="nb">{sec:control}</span>
</div><div id="l801" class="code_block"><span class="nv">\index</span><span class="nb">{control}</span>
</div><div id="l802" class="code_block">
</div><div id="l803" class="code_block"><span class="nv">\begin</span><span class="nb">{description}</span>
</div><div id="l804" class="code_block"><span class="nv">\ouritem</span><span class="nb">{</span><span class="nv">\cut</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{&quot;</span><span class="o">!/</span><span class="m">0</span><span class="nb">}}  </span><span class="nv">\index</span><span class="nb">{cut} </span>
</div><div id="l805" class="code_block"><span class="nb">    Cut </span><span class="o">(</span><span class="nb">discard</span><span class="o">)</span><span class="nb"> all choice points made since the parent goal</span>
</div><div id="l806" class="code_block"><span class="nb">    started execution.</span>
</div><div id="l807" class="code_block"><span class="nb">    Cuts across tabled predicates are not valid.  The compiler checks for</span>
</div><div id="l808" class="code_block"><span class="nb">    such cuts, although whether the scope of a cut includes a tabled </span>
</div><div id="l809" class="code_block"><span class="nb">    predicate is undecidable in the presence of meta</span><span class="o">-</span><span class="nb">predicates like</span>
</div><div id="l810" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> call</span><span class="o">/</span><span class="m">1</span><span class="nb">}.</span>
</div><div id="l811" class="code_block"><span class="nb">    Further discussion of conditions allowing cuts and of their actions </span>
</div><div id="l812" class="code_block"><span class="nb">    can be found in Section~</span><span class="nv">\ref</span><span class="nb">{tabling_env}.</span>
</div><div id="l813" class="code_block">
</div><div id="l814" class="code_block"><span class="nv">\ouritem</span><span class="nb">{fail</span><span class="nv">\_</span><span class="nb">if</span><span class="o">(+</span><span class="nb">P</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{fail</span><span class="nv">\_</span><span class="nb">if</span><span class="o">/</span><span class="m">1</span><span class="nb">}}</span>
</div><div id="l815" class="code_block"><span class="nb">    If the goal {</span><span class="nv">\tt</span><span class="nb"> P} has a solution, fails, otherwise it succeeds.</span>
</div><div id="l816" class="code_block"><span class="nb">    Equivalently, it is true iff {</span><span class="nv">\tt</span><span class="nb"> call</span><span class="o">(</span><span class="nb">P</span><span class="o">)</span><span class="nb">} </span>
</div><div id="l817" class="code_block"><span class="nb">    </span><span class="o">(</span><span class="nb">see Section~</span><span class="nv">\ref</span><span class="nb">{meta_predicates}</span><span class="o">)</span><span class="nb"> is false. Argument {</span><span class="nv">\tt</span><span class="nb"> P} </span>
</div><div id="l818" class="code_block"><span class="nb">    must be ground for sound negation as failure, although no runtime </span>
</div><div id="l819" class="code_block"><span class="nb">    checks are made by the system.</span>
</div><div id="l820" class="code_block">
</div><div id="l821" class="code_block"><span class="nb">    The standard predicate {</span><span class="nv">\tt</span><span class="nb"> fail</span><span class="nv">\_</span><span class="nb">if</span><span class="o">/</span><span class="m">1</span><span class="nb">} is compiled by the </span>
</div><div id="l822" class="code_block"><span class="nb">    XSB compiler.</span>
</div><div id="l823" class="code_block">
</div><div id="l824" class="code_block"><span class="nb">    Exceptions:</span>
</div><div id="l825" class="code_block"><span class="nb">    </span><span class="nv">\begin</span><span class="nb">{description}</span>
</div><div id="l826" class="code_block"><span class="nb">    </span><span class="nv">\item</span><span class="o">[</span><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> instantiation</span><span class="nv">\_</span><span class="nb">error}</span><span class="o">]</span>
</div><div id="l827" class="code_block"><span class="nb">	{</span><span class="nv">\tt</span><span class="nb"> P} is not instantiated.</span>
</div><div id="l828" class="code_block"><span class="nb">    </span><span class="nv">\item</span><span class="o">[</span><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> type</span><span class="nv">\_</span><span class="nb">error}</span><span class="o">]</span>
</div><div id="l829" class="code_block"><span class="nb">	{</span><span class="nv">\tt</span><span class="nb"> P} is not a callable term.</span>
</div><div id="l830" class="code_block"><span class="nb">    </span><span class="nv">\end</span><span class="nb">{description}</span>
</div><div id="l831" class="code_block">
</div><div id="l832" class="code_block">
</div><div id="l833" class="code_block"><span class="nv">\ouritem</span><span class="nb">{</span><span class="s">$</span><span class="k">\backslash</span><span class="s">$</span><span class="o">+</span><span class="nb"> </span><span class="o">+</span><span class="nb">P}</span><span class="nv">\index</span><span class="nb">{</span><span class="s">$</span><span class="k">\backslash</span><span class="s">$</span><span class="nv">\texttt</span><span class="nb">{</span><span class="o">+/</span><span class="m">1</span><span class="nb">}}</span>
</div><div id="l834" class="code_block"><span class="nb">    Exactly the same as {</span><span class="nv">\tt</span><span class="nb"> fail</span><span class="nv">\_</span><span class="nb">if</span><span class="o">/</span><span class="m">1</span><span class="nb">}.  Its existence is only </span>
</div><div id="l835" class="code_block"><span class="nb">    for compatibility with other Prolog systems.</span>
</div><div id="l836" class="code_block">
</div><div id="l837" class="code_block"><span class="nv">\ouritem</span><span class="nb">{not </span><span class="o">+</span><span class="nb">P}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{not</span><span class="o">/</span><span class="m">1</span><span class="nb">}} </span>
</div><div id="l838" class="code_block"><span class="nb">    If the goal {</span><span class="nv">\tt</span><span class="nb"> P} has a solution, fails, otherwise it succeeds.</span>
</div><div id="l839" class="code_block"><span class="nb">    It is defined by:</span>
</div><div id="l840" class="code_block"><span class="nb">    </span><span class="nv">\begin</span><span class="nb">{center}</span>
</div><div id="l841" class="code_block"><span class="nb">    </span><span class="nv">\begin</span><span class="nb">{minipage}{</span><span class="m">2</span><span class="nb">.</span><span class="m">40</span><span class="nb">in}</span>
</div><div id="l842" class="code_block"><span class="nb">    </span><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l843" class="code_block"><span class="nb">	not</span><span class="o">(</span><span class="nb">P</span><span class="o">)</span><span class="nb"> :</span><span class="o">-</span><span class="nb"> call</span><span class="o">(</span><span class="nb">P</span><span class="o">)</span><span class="nb">, </span><span class="o">!</span><span class="nb">, fail.</span>
</div><div id="l844" class="code_block"><span class="nb">	not</span><span class="o">(</span><span class="nb">_</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l845" class="code_block"><span class="nb">    </span><span class="nv">\end</span><span class="nb">{verbatim}</span>
</div><div id="l846" class="code_block"><span class="nb">    </span><span class="nv">\end</span><span class="nb">{minipage}</span>
</div><div id="l847" class="code_block"><span class="nb">    </span><span class="nv">\end</span><span class="nb">{center}</span>
</div><div id="l848" class="code_block">
</div><div id="l849" class="code_block"><span class="nb">    Argument {</span><span class="nv">\tt</span><span class="nb"> P} must be ground for sound negation, although no </span>
</div><div id="l850" class="code_block"><span class="nb">    runtime checks are made by the system.</span>
</div><div id="l851" class="code_block">
</div><div id="l852" class="code_block"><span class="nb">    Note that in contrast to the other two kinds of negation as failure</span>
</div><div id="l853" class="code_block"><span class="nb">    </span><span class="o">(</span><span class="nv">\not\</span><span class="nb"> and {</span><span class="nv">\tt</span><span class="nb"> fail</span><span class="nv">\_</span><span class="nb">if</span><span class="o">/</span><span class="m">1</span><span class="nb">}</span><span class="o">)</span><span class="nb">, predicate {</span><span class="nv">\tt</span><span class="nb"> not</span><span class="o">/</span><span class="m">1</span><span class="nb">} is not compiled</span>
</div><div id="l854" class="code_block"><span class="nb">    by the compiler but the above definition is used.</span>
</div><div id="l855" class="code_block">
</div><div id="l856" class="code_block"><span class="nb">    Exceptions: The same as {</span><span class="nv">\tt</span><span class="nb"> call</span><span class="o">/</span><span class="m">1</span><span class="nb">} </span>
</div><div id="l857" class="code_block"><span class="nb">		</span><span class="o">(</span><span class="nb">see Section~</span><span class="nv">\ref</span><span class="nb">{meta_predicates}</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l858" class="code_block">
</div><div id="l859" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{tnot</span><span class="o">(+</span><span class="nb">P</span><span class="o">)</span><span class="nb">}{Tabling}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{tnot</span><span class="o">/</span><span class="m">1</span><span class="nb">}}</span><span class="nv">\label</span><span class="nb">{tnot</span><span class="o">/</span><span class="m">1</span><span class="nb">}</span>
</div><div id="l860" class="code_block"><span class="nb">    The semantics of {</span><span class="nv">\tt</span><span class="nb"> tnot</span><span class="o">/</span><span class="m">1</span><span class="nb">} allows for correct execution of</span>
</div><div id="l861" class="code_block"><span class="nb">    programs with according to the well</span><span class="o">-</span><span class="nb">founded semantics.  {</span><span class="nv">\tt</span><span class="nb"> P}</span>
</div><div id="l862" class="code_block"><span class="nb">    must be a tabled predicate, </span>
</div><div id="l863" class="code_block"><span class="c">% tls: need to provide an example.</span>
</div><div id="l864" class="code_block"><span class="c">%and the actions of {\tt tnot/1} are</span>
</div><div id="l865" class="code_block"><span class="c">%presented in Figure~\ref{fig:tnot}. </span>
</div><div id="l866" class="code_block"><span class="c">%</span>
</div><div id="l867" class="code_block"><span class="c">%\input{tnot} </span>
</div><div id="l868" class="code_block"><span class="c">%</span>
</div><div id="l869" class="code_block"><span class="nb">    For a detailed description of the actions of tabled negation for</span>
</div><div id="l870" class="code_block"><span class="nb">    in XSB </span><span class="nv">\version\</span><span class="nb"> see~</span><span class="nv">\cite</span><span class="nb">{SaSw</span><span class="m">98</span><span class="nb">, SaSW</span><span class="m">96</span><span class="nb">}.</span>
</div><div id="l871" class="code_block"><span class="nb">    Chapter~</span><span class="nv">\ref</span><span class="nb">{chap:TablingOverview} contains further discussion of the</span>
</div><div id="l872" class="code_block"><span class="nb">    functionality of {</span><span class="nv">\tt</span><span class="nb"> tnot</span><span class="o">/</span><span class="m">1</span><span class="nb">}.</span>
</div><div id="l873" class="code_block">
</div><div id="l874" class="code_block"><span class="nb">    Exceptions:</span>
</div><div id="l875" class="code_block"><span class="nb">    </span><span class="nv">\begin</span><span class="nb">{description}</span>
</div><div id="l876" class="code_block"><span class="nb">    </span><span class="nv">\item</span><span class="o">[</span><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> instantiation</span><span class="nv">\_</span><span class="nb">error}</span><span class="o">]</span>
</div><div id="l877" class="code_block"><span class="nb">	{</span><span class="nv">\tt</span><span class="nb"> P} is not ground </span><span class="o">(</span><span class="nb">floundering occurs</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l878" class="code_block"><span class="nb">    </span><span class="nv">\item</span><span class="o">[</span><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> type</span><span class="nv">\_</span><span class="nb">error}</span><span class="o">]</span>
</div><div id="l879" class="code_block"><span class="nb">	{</span><span class="nv">\tt</span><span class="nb"> P} is not a callable term.</span>
</div><div id="l880" class="code_block"><span class="nb">    </span><span class="nv">\item</span><span class="o">[</span><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> table</span><span class="nv">\_</span><span class="nb">error}</span><span class="o">]</span>
</div><div id="l881" class="code_block"><span class="nb">	{</span><span class="nv">\tt</span><span class="nb"> P} is not a call to a tabled predicate.</span>
</div><div id="l882" class="code_block"><span class="nb">    </span><span class="nv">\end</span><span class="nb">{description}</span>
</div><div id="l883" class="code_block">
</div><div id="l884" class="code_block">
</div><div id="l885" class="code_block"><span class="nb">    </span><span class="nv">\ournewitem</span><span class="nb">{sk</span><span class="nv">\_</span><span class="nb">not</span><span class="o">(+</span><span class="nb">P</span><span class="o">)</span><span class="nb">}{Tabling}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{sk</span><span class="nv">\_</span><span class="nb">not</span><span class="o">/</span><span class="m">1</span><span class="nb">}} </span>
</div><div id="l886" class="code_block"><span class="c">%% </span>
</div><div id="l887" class="code_block"><span class="nb">If {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">+</span><span class="nb">P} is a tabled predicate, {</span><span class="nv">\tt</span><span class="nb"> sk</span><span class="nv">\_</span><span class="nb">not</span><span class="o">/</span><span class="m">1</span><span class="nb">} acts as {</span><span class="nv">\tt</span><span class="nb"> tnot</span><span class="o">/</span><span class="m">1</span><span class="nb">}</span>
</div><div id="l888" class="code_block"><span class="nb">    but permits variables in its subgoal argument.  This replaces the</span>
</div><div id="l889" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> &#39;t not&#39;</span><span class="o">/</span><span class="m">1</span><span class="nb">} predicate of earlier XSB versions whose</span>
</div><div id="l890" class="code_block"><span class="nb">    implementation and semantics were dubious. The semantics in the</span>
</div><div id="l891" class="code_block"><span class="nb">    case of unbound variables is as follows: </span>
</div><div id="l892" class="code_block"><span class="c">%% </span>
</div><div id="l893" class="code_block"><span class="nv">\begin</span><span class="nb">{quote} </span>
</div><div id="l894" class="code_block"><span class="nv">\tt</span><span class="nb"> ... :</span><span class="o">-</span><span class="nb"> ...,~sk</span><span class="nv">\_</span><span class="nb">not</span><span class="o">(</span><span class="nb">p</span><span class="o">(</span><span class="nb">X</span><span class="o">))</span><span class="nb">,~...  </span><span class="nv">\end</span><span class="nb">{quote} </span>
</div><div id="l895" class="code_block"><span class="c">%% </span>
</div><div id="l896" class="code_block"><span class="nb">is equivalent to </span>
</div><div id="l897" class="code_block"><span class="c">%%</span>
</div><div id="l898" class="code_block"><span class="nv">\begin</span><span class="nb">{quote}</span>
</div><div id="l899" class="code_block"><span class="nb"> </span><span class="nv">\tt</span><span class="nb"> ... :</span><span class="o">-</span><span class="nb"> ..., tnot</span><span class="o">(</span><span class="nb">pp</span><span class="o">)</span><span class="nb">,~...</span><span class="nv">\\</span><span class="nb"> pp :</span><span class="o">-</span><span class="nb"> p</span><span class="o">(</span><span class="nb">X</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l900" class="code_block"><span class="nv">\end</span><span class="nb">{quote} </span>
</div><div id="l901" class="code_block"><span class="c">%% </span>
</div><div id="l902" class="code_block"><span class="nb">where {</span><span class="nv">\tt</span><span class="nb"> pp} is a new proposition. Thus, the unbound variable </span><span class="s">$</span>X<span class="s">$</span><span class="nb"> is</span>
</div><div id="l903" class="code_block"><span class="nb">treated as </span><span class="s">$</span><span class="k">\tt</span> tnot(<span class="k">\exists</span> X (p(X)))<span class="s">$</span><span class="nb">.</span>
</div><div id="l904" class="code_block">
</div><div id="l905" class="code_block"><span class="nb">If {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">+</span><span class="nb">P} is a non</span><span class="o">-</span><span class="nb">tabled predicate ensures that {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">+</span><span class="nb">P} is ground</span>
</div><div id="l906" class="code_block"><span class="nb">and called via a tabled predicate so that {</span><span class="nv">\tt</span><span class="nb"> sk</span><span class="nv">\_</span><span class="nb">not</span><span class="o">/</span><span class="m">1</span><span class="nb">} can be used</span>
</div><div id="l907" class="code_block"><span class="nb">with non</span><span class="o">-</span><span class="nb">tabled predicates as well, regardless of whether {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">+</span><span class="nb">P} is</span>
</div><div id="l908" class="code_block"><span class="nb">ground or not.</span>
</div><div id="l909" class="code_block">
</div><div id="l910" class="code_block"><span class="nv">\ouritem</span><span class="nb">{P </span><span class="o">-</span><span class="nb">&gt; Q ; R}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{</span><span class="o">-</span><span class="nb">&gt;</span><span class="o">/</span><span class="m">2</span><span class="nb">}} </span>
</div><div id="l911" class="code_block"><span class="nb">    Analogous to if {</span><span class="nv">\tt</span><span class="nb"> P} then {</span><span class="nv">\tt</span><span class="nb"> Q} else {</span><span class="nv">\tt</span><span class="nb"> R}, i.e.</span><span class="nv">\</span><span class="nb"> defined as </span>
</div><div id="l912" class="code_block"><span class="nb">    if by</span>
</div><div id="l913" class="code_block"><span class="nb">	</span><span class="nv">\begin</span><span class="nb">{center}</span>
</div><div id="l914" class="code_block"><span class="nb">	</span><span class="nv">\begin</span><span class="nb">{minipage}{</span><span class="m">2</span><span class="nb">.</span><span class="m">10</span><span class="nb">in}</span>
</div><div id="l915" class="code_block"><span class="nb">	</span><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l916" class="code_block"><span class="nb">	</span><span class="o">(</span><span class="nb">P </span><span class="o">-</span><span class="nb">&gt; Q ; R</span><span class="o">)</span><span class="nb"> :</span><span class="o">-</span><span class="nb"> P, </span><span class="o">!</span><span class="nb">, Q.</span>
</div><div id="l917" class="code_block"><span class="nb">	</span><span class="o">(</span><span class="nb">P </span><span class="o">-</span><span class="nb">&gt; Q ; R</span><span class="o">)</span><span class="nb"> :</span><span class="o">-</span><span class="nb"> R.</span>
</div><div id="l918" class="code_block"><span class="nb">	</span><span class="nv">\end</span><span class="nb">{verbatim}</span>
</div><div id="l919" class="code_block"><span class="nb">	</span><span class="nv">\end</span><span class="nb">{minipage}</span>
</div><div id="l920" class="code_block"><span class="nb">	</span><span class="nv">\end</span><span class="nb">{center}</span>
</div><div id="l921" class="code_block">
</div><div id="l922" class="code_block"><span class="nv">\ouritem</span><span class="nb">{P </span><span class="o">-</span><span class="nb">&gt; Q} </span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{</span><span class="o">-</span><span class="nb">&gt;</span><span class="o">/</span><span class="m">2</span><span class="nb">}} </span>
</div><div id="l923" class="code_block"><span class="nb">    When occurring other than as one of the alternatives of a disjunction,</span>
</div><div id="l924" class="code_block"><span class="nb">    is equivalent to:</span>
</div><div id="l925" class="code_block"><span class="nb">	</span><span class="nv">\begin</span><span class="nb">{center}</span>
</div><div id="l926" class="code_block"><span class="nb">	{</span><span class="nv">\tt</span><span class="nb"> P </span><span class="o">-</span><span class="nb">&gt; Q ; fail.}</span>
</div><div id="l927" class="code_block"><span class="nb">	</span><span class="nv">\end</span><span class="nb">{center}</span>
</div><div id="l928" class="code_block">
</div><div id="l929" class="code_block"><span class="nv">\ouritem</span><span class="nb">{repeat} </span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{repeat</span><span class="o">/</span><span class="m">2</span><span class="nb">}} </span>
</div><div id="l930" class="code_block"><span class="nb">    Generates an infinite sequence of choice points </span><span class="o">(</span><span class="nb">in other words it </span>
</div><div id="l931" class="code_block"><span class="nb">    provides a very convenient way of executing a loop</span><span class="o">)</span><span class="nb">. It is defined </span>
</div><div id="l932" class="code_block"><span class="nb">    by the clauses:</span>
</div><div id="l933" class="code_block"><span class="nb">    </span><span class="nv">\begin</span><span class="nb">{center}</span>
</div><div id="l934" class="code_block"><span class="nb">    </span><span class="nv">\begin</span><span class="nb">{minipage}{</span><span class="m">1</span><span class="nb">.</span><span class="m">5</span><span class="nb">in}</span>
</div><div id="l935" class="code_block"><span class="nb">    </span><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l936" class="code_block"><span class="nb">	repeat.</span>
</div><div id="l937" class="code_block"><span class="nb">	repeat :</span><span class="o">-</span><span class="nb"> repeat.</span>
</div><div id="l938" class="code_block"><span class="nb">    </span><span class="nv">\end</span><span class="nb">{verbatim}</span>
</div><div id="l939" class="code_block"><span class="nb">    </span><span class="nv">\end</span><span class="nb">{minipage}</span>
</div><div id="l940" class="code_block"><span class="nb">    </span><span class="nv">\end</span><span class="nb">{center}</span>
</div><div id="l941" class="code_block">
</div><div id="l942" class="code_block"><span class="nv">\end</span><span class="nb">{description}</span>
</div><div id="l943" class="code_block">
</div><div id="l944" class="code_block">
</div><div id="l945" class="code_block"><span class="nv">\section</span><span class="nb">{Meta</span><span class="o">-</span><span class="nb">Logical}</span><span class="nv">\label</span><span class="nb">{MetaLogical}</span>
</div><div id="l946" class="code_block">
</div><div id="l947" class="code_block"><span class="nb">To facilitate manipulation of terms as objects in themselves,</span>
</div><div id="l948" class="code_block"><span class="nb">XSB provides a number meta</span><span class="o">-</span><span class="nb">logical predicates.  These</span>
</div><div id="l949" class="code_block"><span class="nb">predicates include the standard meta</span><span class="o">-</span><span class="nb">logical predicates of Prolog,</span>
</div><div id="l950" class="code_block"><span class="nb">along with their usual semantics.  In addition are provided predicates</span>
</div><div id="l951" class="code_block"><span class="nb">which provide special operations on HiLog terms.  For a full</span>
</div><div id="l952" class="code_block"><span class="nb">discussion of Prolog and HiLog terms see Section~</span><span class="nv">\ref</span><span class="nb">{TermSyntax}.</span>
</div><div id="l953" class="code_block">
</div><div id="l954" class="code_block"><span class="nv">\begin</span><span class="nb">{description}</span>
</div><div id="l955" class="code_block"><span class="nv">\ouritem</span><span class="nb">{var</span><span class="o">(</span><span class="nb">?X</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{var</span><span class="o">/</span><span class="m">1</span><span class="nb">}} </span>
</div><div id="l956" class="code_block"><span class="nb">    Succeeds if {</span><span class="nv">\tt</span><span class="nb"> X} is currently uninstantiated </span><span class="o">(</span><span class="nb">i.e.</span><span class="nv">\</span><span class="nb"> is still a </span>
</div><div id="l957" class="code_block"><span class="nb">    variable</span><span class="o">)</span><span class="nb">; otherwise it fails.  </span>
</div><div id="l958" class="code_block">
</div><div id="l959" class="code_block"><span class="nb">    Term {</span><span class="nv">\tt</span><span class="nb"> X} is uninstantiated if it has not been bound to anything, </span>
</div><div id="l960" class="code_block"><span class="nb">    except possibly another uninstantiated variable. Note in particular,</span>
</div><div id="l961" class="code_block"><span class="nb">    that the HiLog term X</span><span class="o">(</span><span class="nb">Y,Z</span><span class="o">)</span><span class="nb"> is considered to be instantiated.  There </span>
</div><div id="l962" class="code_block"><span class="nb">    is no distinction between a Prolog and a HiLog variable.</span>
</div><div id="l963" class="code_block">
</div><div id="l964" class="code_block"><span class="nb">    Examples:</span>
</div><div id="l965" class="code_block"><span class="nb">    {</span><span class="nv">\footnotesize</span>
</div><div id="l966" class="code_block"><span class="nb">     </span><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l967" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> var</span><span class="o">(</span><span class="nb">X</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l968" class="code_block"><span class="nb">                yes</span>
</div><div id="l969" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> var</span><span class="o">([</span><span class="nb">X</span><span class="o">])</span><span class="nb">.</span>
</div><div id="l970" class="code_block"><span class="nb">                no</span>
</div><div id="l971" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> var</span><span class="o">(</span><span class="nb">X</span><span class="o">(</span><span class="nb">Y,Z</span><span class="o">))</span><span class="nb">.</span>
</div><div id="l972" class="code_block"><span class="nb">                no</span>
</div><div id="l973" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> var</span><span class="o">((</span><span class="nb">X</span><span class="o">))</span><span class="nb">.</span>
</div><div id="l974" class="code_block"><span class="nb">                yes</span>
</div><div id="l975" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> var</span><span class="o">((</span><span class="nb">X</span><span class="o">)(</span><span class="nb">Y</span><span class="o">))</span><span class="nb">.</span>
</div><div id="l976" class="code_block"><span class="nb">                no</span>
</div><div id="l977" class="code_block"><span class="nb">     </span><span class="nv">\end</span><span class="nb">{verbatim}}</span>
</div><div id="l978" class="code_block">
</div><div id="l979" class="code_block">
</div><div id="l980" class="code_block"><span class="nv">\ouritem</span><span class="nb">{nonvar</span><span class="o">(</span><span class="nb">?X</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{nonvar</span><span class="o">/</span><span class="m">1</span><span class="nb">}} </span>
</div><div id="l981" class="code_block"><span class="nb">    Succeeds if {</span><span class="nv">\tt</span><span class="nb"> X} is currently instantiated to a non</span><span class="o">-</span><span class="nb">variable term;</span>
</div><div id="l982" class="code_block"><span class="nb">    otherwise it fails. This has exactly the opposite behaviour of </span>
</div><div id="l983" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> var</span><span class="o">/</span><span class="m">1</span><span class="nb">}</span><span class="nv">\@</span><span class="nb">.</span>
</div><div id="l984" class="code_block">
</div><div id="l985" class="code_block"><span class="nv">\ouritem</span><span class="nb">{atom</span><span class="o">(</span><span class="nb">?X</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{atom</span><span class="o">/</span><span class="m">1</span><span class="nb">}} </span>
</div><div id="l986" class="code_block"><span class="nb">    Succeeds only if the {</span><span class="nv">\tt</span><span class="nb"> X} is currently instantiated to an atom, that</span>
</div><div id="l987" class="code_block"><span class="nb">    is to a Prolog or HiLog non</span><span class="o">-</span><span class="nb">numeric constant.</span>
</div><div id="l988" class="code_block">
</div><div id="l989" class="code_block"><span class="nb">    Examples:</span>
</div><div id="l990" class="code_block"><span class="nb">    {</span><span class="nv">\footnotesize</span>
</div><div id="l991" class="code_block"><span class="nb">     </span><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l992" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> atom</span><span class="o">(</span><span class="nb">HiLog</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l993" class="code_block"><span class="nb">                no</span>
</div><div id="l994" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> atom</span><span class="o">(</span><span class="m">10</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l995" class="code_block"><span class="nb">                no</span>
</div><div id="l996" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> atom</span><span class="o">(</span><span class="nb">&#39;HiLog&#39;</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l997" class="code_block"><span class="nb">                yes</span>
</div><div id="l998" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> atom</span><span class="o">(</span><span class="nb">X</span><span class="o">(</span><span class="nb">a,b</span><span class="o">))</span><span class="nb">.</span>
</div><div id="l999" class="code_block"><span class="nb">                no</span>
</div><div id="l1000" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> atom</span><span class="o">(</span><span class="nb">h</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1001" class="code_block"><span class="nb">                yes</span>
</div><div id="l1002" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> atom</span><span class="o">(+)</span><span class="nb">.</span>
</div><div id="l1003" class="code_block"><span class="nb">                yes</span>
</div><div id="l1004" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> atom</span><span class="o">([])</span><span class="nb">.</span>
</div><div id="l1005" class="code_block"><span class="nb">                yes</span>
</div><div id="l1006" class="code_block"><span class="nb">     </span><span class="nv">\end</span><span class="nb">{verbatim}}</span>
</div><div id="l1007" class="code_block">
</div><div id="l1008" class="code_block"><span class="nv">\ouritem</span><span class="nb">{integer</span><span class="o">(</span><span class="nb">?X</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{integer</span><span class="o">/</span><span class="m">1</span><span class="nb">}}</span>
</div><div id="l1009" class="code_block"><span class="nb">    Succeeds if {</span><span class="nv">\tt</span><span class="nb"> X} is currently instantiated to an integer; </span>
</div><div id="l1010" class="code_block"><span class="nb">    otherwise it fails. </span>
</div><div id="l1011" class="code_block">
</div><div id="l1012" class="code_block"><span class="nv">\ouritem</span><span class="nb">{real</span><span class="o">(</span><span class="nb">?X</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{real</span><span class="o">/</span><span class="m">1</span><span class="nb">}} </span>
</div><div id="l1013" class="code_block"><span class="nb">    Succeeds if {</span><span class="nv">\tt</span><span class="nb"> X} is currently instantiated to a floating point number;</span>
</div><div id="l1014" class="code_block"><span class="nb">    otherwise it fails. </span>
</div><div id="l1015" class="code_block">
</div><div id="l1016" class="code_block"><span class="nv">\ouritem</span><span class="nb">{float</span><span class="o">(</span><span class="nb">?X</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{float</span><span class="o">/</span><span class="m">1</span><span class="nb">}} </span>
</div><div id="l1017" class="code_block"><span class="nb">    Same as {</span><span class="nv">\tt</span><span class="nb"> real</span><span class="o">/</span><span class="m">1</span><span class="nb">}. Succeeds if {</span><span class="nv">\tt</span><span class="nb"> X} is currently instantiated </span>
</div><div id="l1018" class="code_block"><span class="nb">    to a floating point number; otherwise it fails.  This predicate is </span>
</div><div id="l1019" class="code_block"><span class="nb">    included for compatibility with earlier versions of SBProlog.</span>
</div><div id="l1020" class="code_block"><span class="nb">	</span>
</div><div id="l1021" class="code_block"><span class="nv">\ouritem</span><span class="nb">{number</span><span class="o">(</span><span class="nb">?X</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{number</span><span class="o">/</span><span class="m">1</span><span class="nb">}} </span>
</div><div id="l1022" class="code_block"><span class="nb">    Succeeds if {</span><span class="nv">\tt</span><span class="nb"> X} is currently instantiated to either an integer or </span>
</div><div id="l1023" class="code_block"><span class="nb">    a floating point number </span><span class="o">(</span><span class="nb">real</span><span class="o">)</span><span class="nb">; otherwise it fails.</span>
</div><div id="l1024" class="code_block">
</div><div id="l1025" class="code_block"><span class="nv">\ouritem</span><span class="nb">{atomic</span><span class="o">(</span><span class="nb">?X</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{atomic</span><span class="o">/</span><span class="m">1</span><span class="nb">}} </span>
</div><div id="l1026" class="code_block"><span class="nb">    Succeeds if {</span><span class="nv">\tt</span><span class="nb"> X} is currently instantiated to an atom or a number;</span>
</div><div id="l1027" class="code_block"><span class="nb">    otherwise it fails.</span>
</div><div id="l1028" class="code_block">
</div><div id="l1029" class="code_block"><span class="nb">    Examples:</span>
</div><div id="l1030" class="code_block"><span class="nb">    {</span><span class="nv">\footnotesize</span>
</div><div id="l1031" class="code_block"><span class="nb">     </span><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l1032" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> atomic</span><span class="o">(</span><span class="m">10</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1033" class="code_block"><span class="nb">                yes</span>
</div><div id="l1034" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> atomic</span><span class="o">(</span><span class="nb">p</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1035" class="code_block"><span class="nb">                yes</span>
</div><div id="l1036" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> atomic</span><span class="o">(</span><span class="nb">h</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1037" class="code_block"><span class="nb">                yes</span>
</div><div id="l1038" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> atomic</span><span class="o">(</span><span class="nb">h</span><span class="o">(</span><span class="nb">X</span><span class="o">))</span><span class="nb">.</span>
</div><div id="l1039" class="code_block"><span class="nb">                no</span>
</div><div id="l1040" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> atomic</span><span class="o">(</span><span class="nb">&quot;foo&quot;</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1041" class="code_block"><span class="nb">                no</span>
</div><div id="l1042" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> atomic</span><span class="o">(</span><span class="nb">&#39;foo&#39;</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1043" class="code_block"><span class="nb">                yes</span>
</div><div id="l1044" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> atomic</span><span class="o">(</span><span class="nb">X</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1045" class="code_block"><span class="nb">                no</span>
</div><div id="l1046" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> atomic</span><span class="o">(</span><span class="nb">X</span><span class="o">((</span><span class="nb">Y</span><span class="o">)))</span><span class="nb">.</span>
</div><div id="l1047" class="code_block"><span class="nb">                no</span>
</div><div id="l1048" class="code_block"><span class="nb">     </span><span class="nv">\end</span><span class="nb">{verbatim}}</span>
</div><div id="l1049" class="code_block">
</div><div id="l1050" class="code_block"><span class="nv">\ouritem</span><span class="nb">{compound</span><span class="o">(</span><span class="nb">?X</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{compound</span><span class="o">/</span><span class="m">1</span><span class="nb">}} </span>
</div><div id="l1051" class="code_block"><span class="nb">    Succeeds if {</span><span class="nv">\tt</span><span class="nb"> X} is currently instantiated to a compound term </span><span class="o">(</span><span class="nb">with </span>
</div><div id="l1052" class="code_block"><span class="nb">    arity greater that zero</span><span class="o">)</span><span class="nb">, i.e.</span><span class="nv">\</span><span class="nb"> to a nonvariable term that is not atomic;</span>
</div><div id="l1053" class="code_block"><span class="nb">    otherwise it fails.</span>
</div><div id="l1054" class="code_block">
</div><div id="l1055" class="code_block"><span class="nb">    Examples:</span>
</div><div id="l1056" class="code_block"><span class="nb">    {</span><span class="nv">\footnotesize</span>
</div><div id="l1057" class="code_block"><span class="nb">     </span><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l1058" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> compound</span><span class="o">(</span><span class="m">1</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1059" class="code_block"><span class="nb">                no</span>
</div><div id="l1060" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> compound</span><span class="o">(</span><span class="nb">foo</span><span class="o">(</span><span class="m">1</span><span class="nb">,</span><span class="m">2</span><span class="nb">,</span><span class="m">3</span><span class="o">))</span><span class="nb">.</span>
</div><div id="l1061" class="code_block"><span class="nb">                yes</span>
</div><div id="l1062" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> compound</span><span class="o">([</span><span class="nb">foo, bar</span><span class="o">])</span><span class="nb">.</span>
</div><div id="l1063" class="code_block"><span class="nb">                yes</span>
</div><div id="l1064" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> compound</span><span class="o">(</span><span class="nb">&quot;foo&quot;</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1065" class="code_block"><span class="nb">                yes</span>
</div><div id="l1066" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> compound</span><span class="o">(</span><span class="nb">&#39;foo&#39;</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1067" class="code_block"><span class="nb">                no</span>
</div><div id="l1068" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> compound</span><span class="o">(</span><span class="nb">X</span><span class="o">(</span><span class="nb">a,b</span><span class="o">))</span><span class="nb">.</span>
</div><div id="l1069" class="code_block"><span class="nb">                yes</span>
</div><div id="l1070" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> compound</span><span class="o">((</span><span class="nb">a,b</span><span class="o">))</span><span class="nb">.</span>
</div><div id="l1071" class="code_block"><span class="nb">                yes	</span>
</div><div id="l1072" class="code_block"><span class="nb">     </span><span class="nv">\end</span><span class="nb">{verbatim}}</span>
</div><div id="l1073" class="code_block">
</div><div id="l1074" class="code_block"><span class="nv">\ouritem</span><span class="nb">{structure</span><span class="o">(</span><span class="nb">?X</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{structure</span><span class="o">/</span><span class="m">1</span><span class="nb">}} </span>
</div><div id="l1075" class="code_block"><span class="nb">    Same as {</span><span class="nv">\tt</span><span class="nb"> compound</span><span class="o">/</span><span class="m">1</span><span class="nb">}</span><span class="nv">\@</span><span class="nb">. Its existence is only for compatibility </span>
</div><div id="l1076" class="code_block"><span class="nb">    with SB</span><span class="o">-</span><span class="nb">Prolog version </span><span class="m">3</span><span class="nb">.</span><span class="m">1</span><span class="nb">.</span>
</div><div id="l1077" class="code_block">
</div><div id="l1078" class="code_block"><span class="nv">\ouritem</span><span class="nb">{is</span><span class="nv">\_</span><span class="nb">list</span><span class="o">(</span><span class="nb">?X</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{is</span><span class="nv">\_</span><span class="nb">list</span><span class="o">/</span><span class="m">1</span><span class="nb">}}</span>
</div><div id="l1079" class="code_block"><span class="nb">    Succeeds if {</span><span class="nv">\tt</span><span class="nb"> X} is a {</span><span class="nv">\em</span><span class="nb"> proper list}. In other words if it is </span>
</div><div id="l1080" class="code_block"><span class="nb">    either the atom {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">[]</span><span class="nb">} or {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">[</span><span class="nb">H|T</span><span class="o">]</span><span class="nb">} where H is any Prolog or HiLog</span>
</div><div id="l1081" class="code_block"><span class="nb">    term and T is a proper list; otherwise it fails.</span>
</div><div id="l1082" class="code_block">
</div><div id="l1083" class="code_block"><span class="nb">    Examples:</span>
</div><div id="l1084" class="code_block"><span class="nb">    {</span><span class="nv">\footnotesize</span>
</div><div id="l1085" class="code_block"><span class="nb">     </span><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l1086" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> is_list</span><span class="o">([</span><span class="nb">p</span><span class="o">(</span><span class="nb">a,b,c</span><span class="o">)</span><span class="nb">, h</span><span class="o">(</span><span class="nb">a,b</span><span class="o">)])</span><span class="nb">.</span>
</div><div id="l1087" class="code_block"><span class="nb">                yes</span>
</div><div id="l1088" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> is_list</span><span class="o">([</span><span class="nb">_,_</span><span class="o">])</span><span class="nb">.</span>
</div><div id="l1089" class="code_block"><span class="nb">                yes</span>
</div><div id="l1090" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> is_list</span><span class="o">([</span><span class="nb">a,b|X</span><span class="o">])</span><span class="nb">.</span>
</div><div id="l1091" class="code_block"><span class="nb">                no</span>
</div><div id="l1092" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> is_list</span><span class="o">([</span><span class="nb">a|b</span><span class="o">])</span><span class="nb">.</span>
</div><div id="l1093" class="code_block"><span class="nb">                no</span>
</div><div id="l1094" class="code_block"><span class="nb">     </span><span class="nv">\end</span><span class="nb">{verbatim}}</span>
</div><div id="l1095" class="code_block">
</div><div id="l1096" class="code_block"><span class="nv">\ouritem</span><span class="nb">{is</span><span class="nv">\_</span><span class="nb">charlist</span><span class="o">(+</span><span class="nb">X</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{is</span><span class="nv">\_</span><span class="nb">charlist</span><span class="o">/</span><span class="m">1</span><span class="nb">}}</span>
</div><div id="l1097" class="code_block"><span class="nb">    Succeeds if {</span><span class="nv">\tt</span><span class="nb"> X} is a Prolog string, {</span><span class="nv">\it</span><span class="nb"> i.e.}, a list of</span>
</div><div id="l1098" class="code_block"><span class="nb">    characters.</span>
</div><div id="l1099" class="code_block"><span class="nb">    Examples:</span>
</div><div id="l1100" class="code_block"><span class="nb">    {</span><span class="nv">\footnotesize</span>
</div><div id="l1101" class="code_block"><span class="nb">     </span><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l1102" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> is_charlist</span><span class="o">(</span><span class="nb">&quot;abc&quot;</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1103" class="code_block"><span class="nb">                yes</span>
</div><div id="l1104" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> is_charlist</span><span class="o">(</span><span class="nb">abc</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1105" class="code_block"><span class="nb">                no</span>
</div><div id="l1106" class="code_block"><span class="nb">     </span><span class="nv">\end</span><span class="nb">{verbatim}}</span>
</div><div id="l1107" class="code_block">
</div><div id="l1108" class="code_block"><span class="nv">\ouritem</span><span class="nb">{is</span><span class="nv">\_</span><span class="nb">charlist</span><span class="o">(+</span><span class="nb">X,</span><span class="o">-</span><span class="nb">Size</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{is</span><span class="nv">\_</span><span class="nb">charlist</span><span class="o">/</span><span class="m">2</span><span class="nb">}}</span>
</div><div id="l1109" class="code_block"><span class="nb">    Works as above, but also returns the length of that string in the second</span>
</div><div id="l1110" class="code_block"><span class="nb">    argument, which must be a variable.</span>
</div><div id="l1111" class="code_block">
</div><div id="l1112" class="code_block"><span class="nv">\ouritem</span><span class="nb">{is</span><span class="nv">\_</span><span class="nb">attv</span><span class="o">(+</span><span class="nb">Term</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{is</span><span class="nv">\_</span><span class="nb">attv</span><span class="o">/</span><span class="m">1</span><span class="nb">}}</span>
</div><div id="l1113" class="code_block"><span class="nb">    Succeeds is {</span><span class="nv">\tt</span><span class="nb"> Term} is an attributed variable, and fails otherwise.</span>
</div><div id="l1114" class="code_block">
</div><div id="l1115" class="code_block"><span class="nv">\ouritem</span><span class="nb">{is</span><span class="nv">\_</span><span class="nb">most</span><span class="nv">\_</span><span class="nb">general</span><span class="nv">\_</span><span class="nb">term</span><span class="o">(</span><span class="nb">?X</span><span class="o">)</span><span class="nb">}</span>
</div><div id="l1116" class="code_block"><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{is</span><span class="nv">\_</span><span class="nb">most</span><span class="nv">\_</span><span class="nb">general</span><span class="nv">\_</span><span class="nb">term</span><span class="o">/</span><span class="m">1</span><span class="nb">}}</span>
</div><div id="l1117" class="code_block"><span class="nb">    Succeeds if {</span><span class="nv">\tt</span><span class="nb"> X} is compound term with all distinct variables</span>
</div><div id="l1118" class="code_block"><span class="nb">as arguments, or if {</span><span class="nv">\tt</span><span class="nb"> X} is an atom. </span><span class="o">(</span><span class="nb">It fails if X is a cons node.</span><span class="o">)</span>
</div><div id="l1119" class="code_block"><span class="nb">    {</span><span class="nv">\footnotesize</span>
</div><div id="l1120" class="code_block"><span class="nb">     </span><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l1121" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> is_most_general_term</span><span class="o">(</span><span class="nb">f</span><span class="o">(</span><span class="nb">_,_,_,_</span><span class="o">))</span><span class="nb">.</span>
</div><div id="l1122" class="code_block"><span class="nb">                yes</span>
</div><div id="l1123" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> is_most_general_term</span><span class="o">(</span><span class="nb">abc</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1124" class="code_block"><span class="nb">                yes</span>
</div><div id="l1125" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> is_most_general_term</span><span class="o">(</span><span class="nb">f</span><span class="o">(</span><span class="nb">X,Y,Z,X</span><span class="o">))</span><span class="nb">.</span>
</div><div id="l1126" class="code_block"><span class="nb">                no</span>
</div><div id="l1127" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> is_most_general_term</span><span class="o">(</span><span class="nb">f</span><span class="o">(</span><span class="nb">X,Y,Z,a</span><span class="o">))</span><span class="nb">.</span>
</div><div id="l1128" class="code_block"><span class="nb">                no</span>
</div><div id="l1129" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> is_most_general_term</span><span class="o">([</span><span class="nb">_|_</span><span class="o">])</span><span class="nb">.</span>
</div><div id="l1130" class="code_block"><span class="nb">                no</span>
</div><div id="l1131" class="code_block"><span class="nb">     </span><span class="nv">\end</span><span class="nb">{verbatim}}</span>
</div><div id="l1132" class="code_block">
</div><div id="l1133" class="code_block"><span class="nv">\ouritem</span><span class="nb">{callable</span><span class="o">(</span><span class="nb">?X</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{callable</span><span class="o">/</span><span class="m">1</span><span class="nb">}}</span>
</div><div id="l1134" class="code_block"><span class="nb">    Succeeds if {</span><span class="nv">\tt</span><span class="nb"> X} is currently instantiated to a term that standard</span>
</div><div id="l1135" class="code_block"><span class="nb">    predicate {</span><span class="nv">\tt</span><span class="nb"> call</span><span class="o">/</span><span class="m">1</span><span class="nb">} could take as an argument and not give an </span>
</div><div id="l1136" class="code_block"><span class="nb">    instantiation or type error.  Note that it only checks for errors of</span>
</div><div id="l1137" class="code_block"><span class="nb">    predicate {</span><span class="nv">\tt</span><span class="nb"> call</span><span class="o">/</span><span class="m">1</span><span class="nb">}.  In other words it succeeds if {</span><span class="nv">\tt</span><span class="nb"> X}</span>
</div><div id="l1138" class="code_block"><span class="nb">    is an atom or a compound term; otherwise it fails.  Predicate</span>
</div><div id="l1139" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> callable</span><span class="o">/</span><span class="m">1</span><span class="nb">} has no associated error conditions.</span>
</div><div id="l1140" class="code_block">
</div><div id="l1141" class="code_block"><span class="nb">    Examples:</span>
</div><div id="l1142" class="code_block"><span class="nb">    {</span><span class="nv">\footnotesize</span>
</div><div id="l1143" class="code_block"><span class="nb">     </span><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l1144" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> callable</span><span class="o">(</span><span class="nb">p</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1145" class="code_block"><span class="nb">                yes</span>
</div><div id="l1146" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> callable</span><span class="o">(</span><span class="nb">p</span><span class="o">(</span><span class="m">1</span><span class="nb">,</span><span class="m">2</span><span class="nb">,</span><span class="m">3</span><span class="o">))</span><span class="nb">.</span>
</div><div id="l1147" class="code_block"><span class="nb">                yes</span>
</div><div id="l1148" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> callable</span><span class="o">([</span><span class="nb">_,_</span><span class="o">])</span><span class="nb">.</span>
</div><div id="l1149" class="code_block"><span class="nb">                yes</span>
</div><div id="l1150" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> callable</span><span class="o">(</span><span class="nb">_</span><span class="o">(</span><span class="nb">a</span><span class="o">))</span><span class="nb">.</span>
</div><div id="l1151" class="code_block"><span class="nb">                yes</span>
</div><div id="l1152" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> callable</span><span class="o">(</span><span class="m">3</span><span class="nb">.</span><span class="m">14</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1153" class="code_block"><span class="nb">                no</span>
</div><div id="l1154" class="code_block"><span class="nb">     </span><span class="nv">\end</span><span class="nb">{verbatim}}</span>
</div><div id="l1155" class="code_block">
</div><div id="l1156" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{proper</span><span class="nv">\_</span><span class="nb">hilog</span><span class="o">(</span><span class="nb">?X</span><span class="o">)</span><span class="nb">}{HiLog}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{proper</span><span class="nv">\_</span><span class="nb">hilog</span><span class="o">/</span><span class="m">1</span><span class="nb">}}</span>
</div><div id="l1157" class="code_block"><span class="nb">    Succeeds if {</span><span class="nv">\tt</span><span class="nb"> X} is a proper HiLog term; otherwise it fails.</span>
</div><div id="l1158" class="code_block">
</div><div id="l1159" class="code_block"><span class="nb">    Examples:</span>
</div><div id="l1160" class="code_block"><span class="nb">    </span><span class="o">(</span><span class="nb">In this example and the rest of the examples of this section we assume</span>
</div><div id="l1161" class="code_block"><span class="nb">     that {</span><span class="nv">\tt</span><span class="nb"> h} is the only parameter symbol that has been declared a HiLog</span>
</div><div id="l1162" class="code_block"><span class="nb">     symbol</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1163" class="code_block">
</div><div id="l1164" class="code_block"><span class="nb">    {</span><span class="nv">\footnotesize</span>
</div><div id="l1165" class="code_block"><span class="nb">     </span><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l1166" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> proper_hilog</span><span class="o">(</span><span class="nb">X</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1167" class="code_block"><span class="nb">                no</span>
</div><div id="l1168" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> proper_hilog</span><span class="o">(</span><span class="nb">foo</span><span class="o">(</span><span class="nb">a,f</span><span class="o">(</span><span class="nb">b</span><span class="o">)</span><span class="nb">,</span><span class="o">[</span><span class="nb">A</span><span class="o">]))</span><span class="nb">.</span>
</div><div id="l1169" class="code_block"><span class="nb">                no</span>
</div><div id="l1170" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> proper_hilog</span><span class="o">(</span><span class="nb">X</span><span class="o">(</span><span class="nb">a,b,c</span><span class="o">))</span><span class="nb">.</span>
</div><div id="l1171" class="code_block"><span class="nb">                yes</span>
</div><div id="l1172" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> proper_hilog</span><span class="o">(</span><span class="m">3</span><span class="nb">.</span><span class="m">6</span><span class="o">(</span><span class="m">2</span><span class="nb">,</span><span class="m">4</span><span class="o">))</span><span class="nb">.</span>
</div><div id="l1173" class="code_block"><span class="nb">                yes</span>
</div><div id="l1174" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> proper_hilog</span><span class="o">(</span><span class="nb">h</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1175" class="code_block"><span class="nb">                no</span>
</div><div id="l1176" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> proper_hilog</span><span class="o">([</span><span class="nb">a, </span><span class="o">[</span><span class="nb">d, e, X</span><span class="o">(</span><span class="nb">a</span><span class="o">)]</span><span class="nb">, c</span><span class="o">])</span><span class="nb">.</span>
</div><div id="l1177" class="code_block"><span class="nb">                yes</span>
</div><div id="l1178" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> proper_hilog</span><span class="o">(</span><span class="nb">a</span><span class="o">(</span><span class="nb">a</span><span class="o">(</span><span class="nb">X</span><span class="o">(</span><span class="nb">a</span><span class="o">))))</span><span class="nb">.</span>
</div><div id="l1179" class="code_block"><span class="nb">                yes</span>
</div><div id="l1180" class="code_block"><span class="nb">     </span><span class="nv">\end</span><span class="nb">{verbatim}}</span>
</div><div id="l1181" class="code_block">
</div><div id="l1182" class="code_block"><span class="nv">\ouritem</span><span class="nb">{functor</span><span class="o">(</span><span class="nb">?Term, ?Functor, ?Arity</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{functor</span><span class="o">/</span><span class="m">3</span><span class="nb">}}</span>
</div><div id="l1183" class="code_block"><span class="nb">    Succeeds if the {</span><span class="nv">\em</span><span class="nb"> functor} of the Prolog term {</span><span class="nv">\tt</span><span class="nb"> Term} is </span>
</div><div id="l1184" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> Functor} and the {</span><span class="nv">\em</span><span class="nb"> arity} </span><span class="o">(</span><span class="nb">number of arguments</span><span class="o">)</span><span class="nb"> of {</span><span class="nv">\tt</span><span class="nb"> Term} is</span>
</div><div id="l1185" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> Arity}</span><span class="nv">\@</span><span class="nb">.  {</span><span class="nv">\tt</span><span class="nb"> Functor} can be used in either the following two </span>
</div><div id="l1186" class="code_block"><span class="nb">    ways:</span>
</div><div id="l1187" class="code_block"><span class="nb">    </span><span class="nv">\begin</span><span class="nb">{enumerate}</span>
</div><div id="l1188" class="code_block"><span class="nb">    </span><span class="nv">\item</span><span class="nb"> If {</span><span class="nv">\tt</span><span class="nb"> Term} is initially instantiated, then</span>
</div><div id="l1189" class="code_block"><span class="nb">          </span><span class="nv">\begin</span><span class="nb">{itemize}</span>
</div><div id="l1190" class="code_block"><span class="nb">          </span><span class="nv">\item</span><span class="nb"> If {</span><span class="nv">\tt</span><span class="nb"> Term} is a compound term, {</span><span class="nv">\tt</span><span class="nb"> Functor} and </span>
</div><div id="l1191" class="code_block"><span class="nb">                {</span><span class="nv">\tt</span><span class="nb"> Arity} are unified with the name and arity of </span>
</div><div id="l1192" class="code_block"><span class="nb">                its principal functor, respectively. </span>
</div><div id="l1193" class="code_block"><span class="nb">          </span><span class="nv">\item</span><span class="nb"> If {</span><span class="nv">\tt</span><span class="nb"> Term} is an atom or a number, {</span><span class="nv">\tt</span><span class="nb"> Functor} is </span>
</div><div id="l1194" class="code_block"><span class="nb">                unified with {</span><span class="nv">\tt</span><span class="nb"> Term}, and {</span><span class="nv">\tt</span><span class="nb"> Arity} is unified with </span><span class="m">0</span><span class="nb">.</span>
</div><div id="l1195" class="code_block"><span class="nb">          </span><span class="nv">\end</span><span class="nb">{itemize}</span>
</div><div id="l1196" class="code_block"><span class="nb">    </span><span class="nv">\item</span><span class="nb"> If {</span><span class="nv">\tt</span><span class="nb"> Term} is initially uninstantiated, then either both </span>
</div><div id="l1197" class="code_block"><span class="nb">          {</span><span class="nv">\tt</span><span class="nb"> Functor} and {</span><span class="nv">\tt</span><span class="nb"> Arity} must be instantiated, or {</span><span class="nv">\tt</span><span class="nb"> Functor}</span>
</div><div id="l1198" class="code_block"><span class="nb">          is instantiated to a number, and</span>
</div><div id="l1199" class="code_block"><span class="nb">          </span><span class="nv">\begin</span><span class="nb">{itemize}</span>
</div><div id="l1200" class="code_block"><span class="nb">          </span><span class="nv">\item</span><span class="nb"> If {</span><span class="nv">\tt</span><span class="nb"> Arity} is an integer in the range </span><span class="m">1</span><span class="nb">..</span><span class="m">255</span><span class="nb">, then</span>
</div><div id="l1201" class="code_block"><span class="nb">                {</span><span class="nv">\tt</span><span class="nb"> Term} becomes instantiated to {</span><span class="nv">\em</span><span class="nb"> the most general </span>
</div><div id="l1202" class="code_block"><span class="nb">                Prolog term} having the specified {</span><span class="nv">\tt</span><span class="nb"> Functor} and </span>
</div><div id="l1203" class="code_block"><span class="nb">                {</span><span class="nv">\tt</span><span class="nb"> Arity} as principal functor and number of arguments,</span>
</div><div id="l1204" class="code_block"><span class="nb">                respectively. The variables appearing as arguments of </span>
</div><div id="l1205" class="code_block"><span class="nb">                {</span><span class="nv">\tt</span><span class="nb"> Term} are all distinct.</span>
</div><div id="l1206" class="code_block"><span class="nb">          </span><span class="nv">\item</span><span class="nb"> If {</span><span class="nv">\tt</span><span class="nb"> Arity} is </span><span class="m">0</span><span class="nb">, then {</span><span class="nv">\tt</span><span class="nb"> Functor} must be either an </span>
</div><div id="l1207" class="code_block"><span class="nb">                atom or a number and it is unified with {</span><span class="nv">\tt</span><span class="nb"> Term}. </span>
</div><div id="l1208" class="code_block"><span class="nb">          </span><span class="nv">\item</span><span class="nb"> If {</span><span class="nv">\tt</span><span class="nb"> Arity} is anything else, then {</span><span class="nv">\tt</span><span class="nb"> functor</span><span class="o">/</span><span class="m">3</span><span class="nb">} aborts.</span>
</div><div id="l1209" class="code_block"><span class="nb">          </span><span class="nv">\end</span><span class="nb">{itemize}</span>
</div><div id="l1210" class="code_block"><span class="nb">    </span><span class="nv">\end</span><span class="nb">{enumerate}</span>
</div><div id="l1211" class="code_block">
</div><div id="l1212" class="code_block"><span class="nb">    Exceptions:</span>
</div><div id="l1213" class="code_block"><span class="nb">    </span><span class="nv">\begin</span><span class="nb">{description}</span>
</div><div id="l1214" class="code_block"><span class="nb">    </span><span class="nv">\item</span><span class="o">[</span><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> domain</span><span class="nv">\_</span><span class="nb">error}</span><span class="o">]</span>
</div><div id="l1215" class="code_block"><span class="nb">	{</span><span class="nv">\tt</span><span class="nb"> Functor} is instantiated to a compound term.</span>
</div><div id="l1216" class="code_block"><span class="nb">    </span><span class="nv">\item</span><span class="o">[</span><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> instantiation</span><span class="nv">\_</span><span class="nb">error}</span><span class="o">]</span>
</div><div id="l1217" class="code_block"><span class="nb">	Both {</span><span class="nv">\tt</span><span class="nb"> Term}, and either {</span><span class="nv">\tt</span><span class="nb"> Functor}, or {</span><span class="nv">\tt</span><span class="nb"> Arity} are </span>
</div><div id="l1218" class="code_block"><span class="nb">	uninstantiated.</span>
</div><div id="l1219" class="code_block"><span class="nb">    </span><span class="nv">\end</span><span class="nb">{description}</span>
</div><div id="l1220" class="code_block">
</div><div id="l1221" class="code_block"><span class="nb">    Examples:</span>
</div><div id="l1222" class="code_block"><span class="nb">    {</span><span class="nv">\footnotesize</span>
</div><div id="l1223" class="code_block"><span class="nb">     </span><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l1224" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> functor</span><span class="o">(</span><span class="nb">p</span><span class="o">(</span><span class="nb">f</span><span class="o">(</span><span class="nb">a</span><span class="o">)</span><span class="nb">,b,t</span><span class="o">)</span><span class="nb">, F, A</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1225" class="code_block"><span class="nb">                F </span><span class="o">=</span><span class="nb"> p</span>
</div><div id="l1226" class="code_block"><span class="nb">                A </span><span class="o">=</span><span class="nb"> </span><span class="m">3</span>
</div><div id="l1227" class="code_block">
</div><div id="l1228" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> functor</span><span class="o">(</span><span class="nb">T, foo, </span><span class="m">3</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1229" class="code_block"><span class="nb">                T </span><span class="o">=</span><span class="nb"> foo</span><span class="o">(</span><span class="nb">_</span><span class="m">595708</span><span class="nb">,_</span><span class="m">595712</span><span class="nb">,_</span><span class="m">595716</span><span class="o">)</span>
</div><div id="l1230" class="code_block">
</div><div id="l1231" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> functor</span><span class="o">(</span><span class="nb">T, </span><span class="m">1</span><span class="nb">.</span><span class="m">3</span><span class="nb">, A</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1232" class="code_block"><span class="nb">                T </span><span class="o">=</span><span class="nb"> </span><span class="m">1</span><span class="nb">.</span><span class="m">3</span>
</div><div id="l1233" class="code_block"><span class="nb">                A </span><span class="o">=</span><span class="nb"> </span><span class="m">0</span>
</div><div id="l1234" class="code_block">
</div><div id="l1235" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> functor</span><span class="o">(</span><span class="nb">foo, F, </span><span class="m">0</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1236" class="code_block"><span class="nb">                F </span><span class="o">=</span><span class="nb"> foo</span>
</div><div id="l1237" class="code_block">
</div><div id="l1238" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> functor</span><span class="o">(</span><span class="nb">&quot;foo&quot;, F, A</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1239" class="code_block"><span class="nb">                F </span><span class="o">=</span><span class="nb"> .</span>
</div><div id="l1240" class="code_block"><span class="nb">                A </span><span class="o">=</span><span class="nb"> </span><span class="m">2</span>
</div><div id="l1241" class="code_block">
</div><div id="l1242" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> functor</span><span class="o">([]</span><span class="nb">, </span><span class="o">[]</span><span class="nb">, A</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1243" class="code_block"><span class="nb">                A </span><span class="o">=</span><span class="nb"> </span><span class="m">0</span>
</div><div id="l1244" class="code_block">
</div><div id="l1245" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> functor</span><span class="o">([</span><span class="m">2</span><span class="nb">,</span><span class="m">3</span><span class="nb">,</span><span class="m">4</span><span class="o">]</span><span class="nb">, F, A</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1246" class="code_block"><span class="nb">                F </span><span class="o">=</span><span class="nb"> .</span>
</div><div id="l1247" class="code_block"><span class="nb">                A </span><span class="o">=</span><span class="nb"> </span><span class="m">2</span>
</div><div id="l1248" class="code_block">
</div><div id="l1249" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> functor</span><span class="o">(</span><span class="nb">a</span><span class="o">+</span><span class="nb">b, F, A</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1250" class="code_block"><span class="nb">                F </span><span class="o">=</span><span class="nb"> </span><span class="o">+</span>
</div><div id="l1251" class="code_block"><span class="nb">                A </span><span class="o">=</span><span class="nb"> </span><span class="m">2</span>
</div><div id="l1252" class="code_block">
</div><div id="l1253" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> functor</span><span class="o">(</span><span class="nb">f</span><span class="o">(</span><span class="nb">a,b,c</span><span class="o">)</span><span class="nb">, F, A</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1254" class="code_block"><span class="nb">                F </span><span class="o">=</span><span class="nb"> f</span>
</div><div id="l1255" class="code_block"><span class="nb">                A </span><span class="o">=</span><span class="nb"> </span><span class="m">3</span>
</div><div id="l1256" class="code_block">
</div><div id="l1257" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> functor</span><span class="o">(</span><span class="nb">X</span><span class="o">(</span><span class="nb">a,b,c</span><span class="o">)</span><span class="nb">, F, A</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1258" class="code_block"><span class="nb">                F </span><span class="o">=</span><span class="nb"> apply</span>
</div><div id="l1259" class="code_block"><span class="nb">                A </span><span class="o">=</span><span class="nb"> </span><span class="m">4</span>
</div><div id="l1260" class="code_block">
</div><div id="l1261" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> functor</span><span class="o">(</span><span class="nb">map</span><span class="o">(</span><span class="nb">P</span><span class="o">)(</span><span class="nb">a,b</span><span class="o">)</span><span class="nb">, F, A</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1262" class="code_block"><span class="nb">                F </span><span class="o">=</span><span class="nb"> apply</span>
</div><div id="l1263" class="code_block"><span class="nb">                A </span><span class="o">=</span><span class="nb"> </span><span class="m">3</span>
</div><div id="l1264" class="code_block">
</div><div id="l1265" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> functor</span><span class="o">(</span><span class="nb">T, foo</span><span class="o">(</span><span class="nb">a</span><span class="o">)</span><span class="nb">, </span><span class="m">1</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1266" class="code_block"><span class="nb">                </span><span class="o">++</span><span class="nb">Error: Wrong type in argument </span><span class="m">2</span><span class="nb"> of functor</span><span class="o">/</span><span class="m">3</span>
</div><div id="l1267" class="code_block"><span class="nb">                Aborting...</span>
</div><div id="l1268" class="code_block">
</div><div id="l1269" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> functor</span><span class="o">(</span><span class="nb">T, F, </span><span class="m">3</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1270" class="code_block"><span class="nb">                </span><span class="o">++</span><span class="nb">Error: Uninstantiated argument </span><span class="m">2</span><span class="nb"> of functor</span><span class="o">/</span><span class="m">3</span>
</div><div id="l1271" class="code_block"><span class="nb">                Aborting...</span>
</div><div id="l1272" class="code_block">
</div><div id="l1273" class="code_block"><span class="nb">                | ?</span><span class="o">-</span><span class="nb"> functor</span><span class="o">(</span><span class="nb">T, foo, A</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1274" class="code_block"><span class="nb">                </span><span class="o">++</span><span class="nb">Error: Uninstantiated argument </span><span class="m">3</span><span class="nb"> of functor</span><span class="o">/</span><span class="m">3</span>
</div><div id="l1275" class="code_block"><span class="nb">                Aborting...</span>
</div><div id="l1276" class="code_block"><span class="nb">     </span><span class="nv">\end</span><span class="nb">{verbatim}}</span>
</div><div id="l1277" class="code_block">
</div><div id="l1278" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{hilog</span><span class="nv">\_</span><span class="nb">functor</span><span class="o">(</span><span class="nb">?Term, ?F, ?Arity</span><span class="o">)</span><span class="nb">}{HiLog}</span>
</div><div id="l1279" class="code_block"><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{hilog</span><span class="nv">\_</span><span class="nb">functor</span><span class="o">/</span><span class="m">3</span><span class="nb">}}</span>
</div><div id="l1280" class="code_block"><span class="nb">    The XSB standard predicate {</span><span class="nv">\tt</span><span class="nb"> hilog</span><span class="nv">\_</span><span class="nb">functor</span><span class="o">/</span><span class="m">3</span><span class="nb">} succeeds </span>
</div><div id="l1281" class="code_block"><span class="nb">    </span><span class="nv">\begin</span><span class="nb">{itemize}</span>
</div><div id="l1282" class="code_block"><span class="nb">    </span><span class="nv">\item</span><span class="nb"> when {</span><span class="nv">\tt</span><span class="nb"> Term} is a Prolog term and the principal function </span>
</div><div id="l1283" class="code_block"><span class="nb">          symbol </span><span class="o">(</span><span class="nb">{</span><span class="nv">\em</span><span class="nb"> functor}</span><span class="o">)</span><span class="nb"> of {</span><span class="nv">\tt</span><span class="nb"> Term} is {</span><span class="nv">\tt</span><span class="nb"> F} and the</span>
</div><div id="l1284" class="code_block"><span class="nb">          {</span><span class="nv">\em</span><span class="nb"> arity} </span><span class="o">(</span><span class="nb">number of arguments</span><span class="o">)</span><span class="nb"> of {</span><span class="nv">\tt</span><span class="nb"> Term} is </span>
</div><div id="l1285" class="code_block"><span class="nb">          {</span><span class="nv">\tt</span><span class="nb"> Arity}, or</span>
</div><div id="l1286" class="code_block"><span class="nb">    </span><span class="nv">\item</span><span class="nb"> when {</span><span class="nv">\tt</span><span class="nb"> Term} is a HiLog term, having {</span><span class="nv">\em</span><span class="nb"> name} {</span><span class="nv">\tt</span><span class="nb"> F} </span>
</div><div id="l1287" class="code_block"><span class="nb">          and the number of arguments {</span><span class="nv">\tt</span><span class="nb"> F} is applied to, in the </span>
</div><div id="l1288" class="code_block"><span class="nb">          HiLog term, is {</span><span class="nv">\tt</span><span class="nb"> Arity}.</span>
</div><div id="l1289" class="code_block"><span class="nb">    </span><span class="nv">\end</span><span class="nb">{itemize}</span>
</div><div id="l1290" class="code_block"><span class="nb">    The first of these cases corresponds to the ``usual&#39;&#39; behaviour of</span>
</div><div id="l1291" class="code_block"><span class="nb">    Prolog&#39;s {</span><span class="nv">\tt</span><span class="nb"> functor</span><span class="o">/</span><span class="m">3</span><span class="nb">}, while the second is the extension of</span>
</div><div id="l1292" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> functor</span><span class="o">/</span><span class="m">3</span><span class="nb">} to handle HiLog terms. Like the Prolog&#39;s {</span><span class="nv">\tt</span>
</div><div id="l1293" class="code_block"><span class="nb">    functor</span><span class="o">/</span><span class="m">3</span><span class="nb">} predicate, {</span><span class="nv">\tt</span><span class="nb"> hilog</span><span class="nv">\_</span><span class="nb">functor</span><span class="o">/</span><span class="m">3</span><span class="nb">} can be used in either</span>
</div><div id="l1294" class="code_block"><span class="nb">    of the following two ways:</span>
</div><div id="l1295" class="code_block"><span class="nb">    </span><span class="nv">\begin</span><span class="nb">{enumerate}</span>
</div><div id="l1296" class="code_block"><span class="nb">    </span><span class="nv">\item</span><span class="nb"> If {</span><span class="nv">\tt</span><span class="nb"> Term} is initially instantiated, then</span>
</div><div id="l1297" class="code_block"><span class="nb">          </span><span class="nv">\begin</span><span class="nb">{itemize}</span>
</div><div id="l1298" class="code_block"><span class="nb">          </span><span class="nv">\item</span><span class="nb"> If {</span><span class="nv">\tt</span><span class="nb"> Term} is a Prolog compound term, {</span><span class="nv">\tt</span><span class="nb"> F} and </span>
</div><div id="l1299" class="code_block"><span class="nb">                {</span><span class="nv">\tt</span><span class="nb"> Arity} are unified with the name and arity of </span>
</div><div id="l1300" class="code_block"><span class="nb">                its principal functor, respectively.</span>
</div><div id="l1301" class="code_block"><span class="nb">          </span><span class="nv">\item</span><span class="nb"> If {</span><span class="nv">\tt</span><span class="nb"> Term} is an atom or a number, {</span><span class="nv">\tt</span><span class="nb"> F} is unified </span>
</div><div id="l1302" class="code_block"><span class="nb">                with {</span><span class="nv">\tt</span><span class="nb"> Term}, and {</span><span class="nv">\tt</span><span class="nb"> Arity} is unified with </span><span class="m">0</span><span class="nb">.</span>
</div><div id="l1303" class="code_block"><span class="nb">          </span><span class="nv">\item</span><span class="nb"> If {</span><span class="nv">\tt</span><span class="nb"> Term} is any other HiLog term, {</span><span class="nv">\tt</span><span class="nb"> F} and {</span><span class="nv">\tt</span><span class="nb"> Arity} </span>
</div><div id="l1304" class="code_block"><span class="nb">                are unified with the name and the number of arguments </span>
</div><div id="l1305" class="code_block"><span class="nb">                that {</span><span class="nv">\tt</span><span class="nb"> F} is applied to. Note that in this case {</span><span class="nv">\tt</span><span class="nb"> F}</span>
</div><div id="l1306" class="code_block"><span class="nb">                may still be uninstantiated.</span>
</div><div id="l1307" class="code_block"><span class="nb">          </span><span class="nv">\end</span><span class="nb">{itemize}</span>
</div><div id="l1308" class="code_block"><span class="nb">    </span><span class="nv">\item</span><span class="nb"> If {</span><span class="nv">\tt</span><span class="nb"> Term} is initially uninstantiated, then at least</span>
</div><div id="l1309" class="code_block"><span class="nb">          {</span><span class="nv">\tt</span><span class="nb"> Arity} must be instantiated, and</span>
</div><div id="l1310" class="code_block"><span class="nb">          </span><span class="nv">\begin</span><span class="nb">{itemize}</span>
</div><div id="l1311" class="code_block"><span class="nb">          </span><span class="nv">\item</span><span class="nb"> If {</span><span class="nv">\tt</span><span class="nb"> Arity} is an integer in the range </span><span class="m">1</span><span class="nb">..</span><span class="m">255</span><span class="nb">, then</span>
</div><div id="l1312" class="code_block"><span class="nb">                {</span><span class="nv">\tt</span><span class="nb"> Term} becomes instantiated to {</span><span class="nv">\em</span><span class="nb"> the most general </span>
</div><div id="l1313" class="code_block"><span class="nb">                Prolog or HiLog term} having the specified {</span><span class="nv">\tt</span><span class="nb"> F} and </span>
</div><div id="l1314" class="code_block"><span class="nb">                {</span><span class="nv">\tt</span><span class="nb"> Arity} as name and number of arguments {</span><span class="nv">\tt</span><span class="nb"> F} is </span>
</div><div id="l1315" class="code_block"><span class="nb">                applied to, respectively. The variables appearing as </span>
</div><div id="l1316" class="code_block"><span class="nb">                arguments are all unique.</span>
</div><div id="l1317" class="code_block"><span class="nb">          </span><span class="nv">\item</span><span class="nb"> If {</span><span class="nv">\tt</span><span class="nb"> Arity} is </span><span class="m">0</span><span class="nb">, then {</span><span class="nv">\tt</span><span class="nb"> F} must be a Prolog or</span>
</div><div id="l1318" class="code_block"><span class="nb">                HiLog constant, and it is unified with {</span><span class="nv">\tt</span><span class="nb"> Term}</span><span class="nv">\@</span><span class="nb">. Note</span>
</div><div id="l1319" class="code_block"><span class="nb">                that in this case {</span><span class="nv">\tt</span><span class="nb"> F} cannot be a compound term.</span>
</div><div id="l1320" class="code_block"><span class="nb">          </span><span class="nv">\item</span><span class="nb"> If {</span><span class="nv">\tt</span><span class="nb"> Arity} is anything else, then {</span><span class="nv">\tt</span><span class="nb"> hilog</span><span class="nv">\_</span><span class="nb">functor</span><span class="o">/</span><span class="m">3</span><span class="nb">}</span>
</div><div id="l1321" class="code_block"><span class="nb">                aborts.</span>
</div><div id="l1322" class="code_block"><span class="nb">          </span><span class="nv">\end</span><span class="nb">{itemize}</span>
</div><div id="l1323" class="code_block"><span class="nb">    </span><span class="nv">\end</span><span class="nb">{enumerate}</span>
</div><div id="l1324" class="code_block"><span class="nb">    In other words, the standard predicate {</span><span class="nv">\tt</span><span class="nb"> hilog</span><span class="nv">\_</span><span class="nb">functor</span><span class="o">/</span><span class="m">3</span><span class="nb">} either</span>
</div><div id="l1325" class="code_block"><span class="nb">    decomposes a given HiLog term into its {</span><span class="nv">\em</span><span class="nb"> name} and {</span><span class="nv">\em</span><span class="nb"> arity}, or</span>
</div><div id="l1326" class="code_block"><span class="nb">    given an arity </span><span class="o">---</span><span class="nb">and possibly a name</span><span class="o">---</span><span class="nb"> constructs the corresponding </span>
</div><div id="l1327" class="code_block"><span class="nb">    HiLog term creating new uninstantiated variables for its arguments. </span>
</div><div id="l1328" class="code_block"><span class="nb">    As happens with {</span><span class="nv">\tt</span><span class="nb"> functor</span><span class="o">/</span><span class="m">3</span><span class="nb">} all constants can be their own </span>
</div><div id="l1329" class="code_block"><span class="nb">    principal function symbols.</span>
</div><div id="l1330" class="code_block">
</div><div id="l1331" class="code_block"><span class="nb">    Examples:</span>
</div><div id="l1332" class="code_block"><span class="nb">    {</span><span class="nv">\footnotesize</span>
</div><div id="l1333" class="code_block"><span class="nb">     </span><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l1334" class="code_block"><span class="nb">               | ?</span><span class="o">-</span><span class="nb"> hilog_functor</span><span class="o">(</span><span class="nb">f</span><span class="o">(</span><span class="nb">a,b,c</span><span class="o">)</span><span class="nb">, F, A</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1335" class="code_block"><span class="nb">               F </span><span class="o">=</span><span class="nb"> f</span>
</div><div id="l1336" class="code_block"><span class="nb">               A </span><span class="o">=</span><span class="nb"> </span><span class="m">3</span>
</div><div id="l1337" class="code_block">
</div><div id="l1338" class="code_block"><span class="nb">               | ?</span><span class="o">-</span><span class="nb"> hilog_functor</span><span class="o">(</span><span class="nb">X</span><span class="o">(</span><span class="nb">a,b,c</span><span class="o">)</span><span class="nb">, F, A</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1339" class="code_block"><span class="nb">               X </span><span class="o">=</span><span class="nb"> _</span><span class="m">595836</span>
</div><div id="l1340" class="code_block"><span class="nb">               F </span><span class="o">=</span><span class="nb"> _</span><span class="m">595836</span>
</div><div id="l1341" class="code_block"><span class="nb">               A </span><span class="o">=</span><span class="nb"> </span><span class="m">3</span>
</div><div id="l1342" class="code_block">
</div><div id="l1343" class="code_block"><span class="nb">               | ?</span><span class="o">-</span><span class="nb"> hilog_functor</span><span class="o">(</span><span class="nb">map</span><span class="o">(</span><span class="nb">P</span><span class="o">)(</span><span class="nb">a,b</span><span class="o">)</span><span class="nb">, F, A</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1344" class="code_block"><span class="nb">               P </span><span class="o">=</span><span class="nb"> _</span><span class="m">595828</span>
</div><div id="l1345" class="code_block"><span class="nb">               F </span><span class="o">=</span><span class="nb"> map</span><span class="o">(</span><span class="nb">_</span><span class="m">595828</span><span class="o">)</span>
</div><div id="l1346" class="code_block"><span class="nb">               A </span><span class="o">=</span><span class="nb"> </span><span class="m">2</span>
</div><div id="l1347" class="code_block">
</div><div id="l1348" class="code_block"><span class="nb">               | ?</span><span class="o">-</span><span class="nb"> hilog_functor</span><span class="o">(</span><span class="nb">T, p, </span><span class="m">2</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1349" class="code_block"><span class="nb">               T </span><span class="o">=</span><span class="nb"> p</span><span class="o">(</span><span class="nb">_</span><span class="m">595708</span><span class="nb">,_</span><span class="m">595712</span><span class="o">)</span>
</div><div id="l1350" class="code_block">
</div><div id="l1351" class="code_block"><span class="nb">               | ?</span><span class="o">-</span><span class="nb"> hilog_functor</span><span class="o">(</span><span class="nb">T, h, </span><span class="m">2</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1352" class="code_block"><span class="nb">               T </span><span class="o">=</span><span class="nb"> apply</span><span class="o">(</span><span class="nb">h,_</span><span class="m">595712</span><span class="nb">,_</span><span class="m">595716</span><span class="o">)</span>
</div><div id="l1353" class="code_block">
</div><div id="l1354" class="code_block"><span class="nb">               | ?</span><span class="o">-</span><span class="nb"> hilog_functor</span><span class="o">(</span><span class="nb">T, X, </span><span class="m">3</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1355" class="code_block"><span class="nb">               T </span><span class="o">=</span><span class="nb"> apply</span><span class="o">(</span><span class="nb">_</span><span class="m">595592</span><span class="nb">,_</span><span class="m">595736</span><span class="nb">,_</span><span class="m">595740</span><span class="nb">,_</span><span class="m">595744</span><span class="o">)</span>
</div><div id="l1356" class="code_block"><span class="nb">               X </span><span class="o">=</span><span class="nb"> _</span><span class="m">595592</span>
</div><div id="l1357" class="code_block">
</div><div id="l1358" class="code_block"><span class="nb">               | ?</span><span class="o">-</span><span class="nb"> hilog_functor</span><span class="o">(</span><span class="nb">T, p</span><span class="o">(</span><span class="nb">f</span><span class="o">(</span><span class="nb">a</span><span class="o">))</span><span class="nb">, </span><span class="m">2</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1359" class="code_block"><span class="nb">               T </span><span class="o">=</span><span class="nb"> apply</span><span class="o">(</span><span class="nb">p</span><span class="o">(</span><span class="nb">f</span><span class="o">(</span><span class="nb">a</span><span class="o">))</span><span class="nb">,_</span><span class="m">595792</span><span class="nb">,_</span><span class="m">595796</span><span class="o">)</span>
</div><div id="l1360" class="code_block">
</div><div id="l1361" class="code_block"><span class="nb">               | ?</span><span class="o">-</span><span class="nb"> hilog_functor</span><span class="o">(</span><span class="nb">T, h</span><span class="o">(</span><span class="nb">p</span><span class="o">(</span><span class="nb">a</span><span class="o">))(</span><span class="nb">L</span><span class="m">1</span><span class="nb">,L</span><span class="m">2</span><span class="o">)</span><span class="nb">, </span><span class="m">1</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1362" class="code_block"><span class="nb">               T </span><span class="o">=</span><span class="nb"> apply</span><span class="o">(</span><span class="nb">apply</span><span class="o">(</span><span class="nb">apply</span><span class="o">(</span><span class="nb">h,p</span><span class="o">(</span><span class="nb">a</span><span class="o">))</span><span class="nb">,_</span><span class="m">595984</span><span class="nb">,_</span><span class="m">595776</span><span class="o">)</span><span class="nb">,_</span><span class="m">596128</span><span class="o">)</span>
</div><div id="l1363" class="code_block"><span class="nb">               L</span><span class="m">1</span><span class="nb"> </span><span class="o">=</span><span class="nb"> _</span><span class="m">595984</span>
</div><div id="l1364" class="code_block"><span class="nb">               L</span><span class="m">2</span><span class="nb"> </span><span class="o">=</span><span class="nb"> _</span><span class="m">595776</span>
</div><div id="l1365" class="code_block">
</div><div id="l1366" class="code_block"><span class="nb">               | ?</span><span class="o">-</span><span class="nb"> hilog_functor</span><span class="o">(</span><span class="nb">T, a</span><span class="o">+</span><span class="nb">b, </span><span class="m">3</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1367" class="code_block"><span class="nb">               T </span><span class="o">=</span><span class="nb"> apply</span><span class="o">(</span><span class="nb">a</span><span class="o">+</span><span class="nb">b,_</span><span class="m">595820</span><span class="nb">,_</span><span class="m">595824</span><span class="nb">,_</span><span class="m">595828</span><span class="o">)</span>
</div><div id="l1368" class="code_block"><span class="nb">     </span><span class="nv">\end</span><span class="nb">{verbatim}}</span>
</div><div id="l1369" class="code_block">
</div><div id="l1370" class="code_block"><span class="nv">\ouritem</span><span class="nb">{arg</span><span class="o">(+</span><span class="nb">Index, </span><span class="o">+</span><span class="nb">Term, ?Argument</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{arg</span><span class="o">/</span><span class="m">3</span><span class="nb">}}</span>
</div><div id="l1371" class="code_block"><span class="nb">    Unifies {</span><span class="nv">\tt</span><span class="nb"> Argument} with the </span><span class="s">$</span><span class="nb">{</span><span class="k">\tt</span> Index<span class="nb">}^{</span>th<span class="nb">}</span><span class="s">$</span><span class="nb"> argument of </span>
</div><div id="l1372" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> Term}</span><span class="nv">\@</span><span class="nb">, where the index is taken to start at </span><span class="s">$</span>1<span class="s">$</span><span class="nb">.</span>
</div><div id="l1373" class="code_block"><span class="nb">    Initially, {</span><span class="nv">\tt</span><span class="nb"> Index} must be instantiated to any integer and {</span><span class="nv">\tt</span><span class="nb"> Term} </span>
</div><div id="l1374" class="code_block"><span class="nb">    to any non</span><span class="o">-</span><span class="nb">variable Prolog or HiLog term.</span>
</div><div id="l1375" class="code_block"><span class="nb">    The arguments of the {</span><span class="nv">\tt</span><span class="nb"> Term} are numbered from~</span><span class="m">1</span><span class="nb"> upwards. An atomic term</span>
</div><div id="l1376" class="code_block"><span class="nb">    has </span><span class="s">$</span>0<span class="s">$</span><span class="nb"> arguments. If the initial conditions are not satisfied or~</span><span class="s">$</span>I<span class="s">$</span><span class="nb"> is </span>
</div><div id="l1377" class="code_block"><span class="nb">    out of range, the call quietly fails.</span>
</div><div id="l1378" class="code_block">
</div><div id="l1379" class="code_block"><span class="nb">    Examples:</span>
</div><div id="l1380" class="code_block"><span class="nb">    {</span><span class="nv">\footnotesize</span>
</div><div id="l1381" class="code_block"><span class="nb">     </span><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l1382" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> arg</span><span class="o">(</span><span class="m">2</span><span class="nb">, p</span><span class="o">(</span><span class="nb">a,b</span><span class="o">)</span><span class="nb">, A</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1383" class="code_block"><span class="nb">                   A </span><span class="o">=</span><span class="nb"> b</span>
</div><div id="l1384" class="code_block">
</div><div id="l1385" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> arg</span><span class="o">(</span><span class="m">2</span><span class="nb">, h</span><span class="o">(</span><span class="nb">a,b</span><span class="o">)</span><span class="nb">, A</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1386" class="code_block"><span class="nb">                   A </span><span class="o">=</span><span class="nb"> a</span>
</div><div id="l1387" class="code_block">
</div><div id="l1388" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> arg</span><span class="o">(</span><span class="m">0</span><span class="nb">, foo, A</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1389" class="code_block"><span class="nb">                   no</span>
</div><div id="l1390" class="code_block">
</div><div id="l1391" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> arg</span><span class="o">(</span><span class="m">2</span><span class="nb">, </span><span class="o">[</span><span class="nb">a,b,c</span><span class="o">]</span><span class="nb">, A</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1392" class="code_block"><span class="nb">                   A </span><span class="o">=</span><span class="nb"> </span><span class="o">[</span><span class="nb">b,c</span><span class="o">]</span>
</div><div id="l1393" class="code_block">
</div><div id="l1394" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> arg</span><span class="o">(</span><span class="m">2</span><span class="nb">, &quot;HiLog&quot;, A</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1395" class="code_block"><span class="nb">                   A </span><span class="o">=</span><span class="nb"> </span><span class="o">[</span><span class="m">105</span><span class="nb">,</span><span class="m">108</span><span class="nb">,</span><span class="m">111</span><span class="nb">,</span><span class="m">103</span><span class="o">]</span>
</div><div id="l1396" class="code_block">
</div><div id="l1397" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> arg</span><span class="o">(</span><span class="m">2</span><span class="nb">, a</span><span class="o">+</span><span class="nb">b</span><span class="o">+</span><span class="nb">c, A</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1398" class="code_block"><span class="nb">                   A </span><span class="o">=</span><span class="nb"> c</span>
</div><div id="l1399" class="code_block">
</div><div id="l1400" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> arg</span><span class="o">(</span><span class="m">3</span><span class="nb">, X</span><span class="o">(</span><span class="nb">a,b,c</span><span class="o">)</span><span class="nb">, A</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1401" class="code_block"><span class="nb">                   X </span><span class="o">=</span><span class="nb"> _</span><span class="m">595820</span><span class="nb"> </span>
</div><div id="l1402" class="code_block"><span class="nb">                   A </span><span class="o">=</span><span class="nb"> b </span>
</div><div id="l1403" class="code_block">
</div><div id="l1404" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> arg</span><span class="o">(</span><span class="m">2</span><span class="nb">, map</span><span class="o">(</span><span class="nb">f</span><span class="o">)(</span><span class="nb">a,b</span><span class="o">)</span><span class="nb">, A</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1405" class="code_block"><span class="nb">                   A </span><span class="o">=</span><span class="nb"> a</span>
</div><div id="l1406" class="code_block">
</div><div id="l1407" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> arg</span><span class="o">(</span><span class="m">1</span><span class="nb">, map</span><span class="o">(</span><span class="nb">f</span><span class="o">)(</span><span class="nb">a,b</span><span class="o">)</span><span class="nb">, A</span><span class="o">)</span><span class="nb">. </span>
</div><div id="l1408" class="code_block"><span class="nb">                   A </span><span class="o">=</span><span class="nb"> map</span><span class="o">(</span><span class="nb">f</span><span class="o">)</span>
</div><div id="l1409" class="code_block">
</div><div id="l1410" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> arg</span><span class="o">(</span><span class="m">1</span><span class="nb">, </span><span class="o">(</span><span class="nb">a</span><span class="o">+</span><span class="nb">b</span><span class="o">)(</span><span class="nb">foo,bar</span><span class="o">)</span><span class="nb">, A</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1411" class="code_block"><span class="nb">                   A </span><span class="o">=</span><span class="nb"> a</span><span class="o">+</span><span class="nb">b</span>
</div><div id="l1412" class="code_block"><span class="nb">     </span><span class="nv">\end</span><span class="nb">{verbatim}}</span>
</div><div id="l1413" class="code_block">
</div><div id="l1414" class="code_block"><span class="nv">\ouritem</span><span class="nb">{arg</span><span class="m">0</span><span class="o">(+</span><span class="nb">Index, </span><span class="o">+</span><span class="nb">Term, ?Argument</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{arg</span><span class="m">0</span><span class="o">/</span><span class="m">3</span><span class="nb">}}</span>
</div><div id="l1415" class="code_block"><span class="nb">    Unifies {</span><span class="nv">\tt</span><span class="nb"> Argument} with the </span><span class="s">$</span><span class="nb">{</span><span class="k">\tt</span> Index<span class="nb">}^{</span>th<span class="nb">}</span><span class="s">$</span><span class="nb"> argument of {</span><span class="nv">\tt</span><span class="nb"> Term}</span>
</div><div id="l1416" class="code_block"><span class="nb">    if {</span><span class="nv">\tt</span><span class="nb"> Index} </span><span class="s">$</span>&gt;<span class="s">$</span><span class="nb"> </span><span class="m">0</span><span class="nb">, or with the functor of {</span><span class="nv">\tt</span><span class="nb"> Term} if {</span><span class="nv">\tt</span><span class="nb"> Index} </span><span class="o">=</span><span class="nb"> </span><span class="m">0</span><span class="nb">.</span>
</div><div id="l1417" class="code_block">
</div><div id="l1418" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{hilog</span><span class="nv">\_</span><span class="nb">arg</span><span class="o">(+</span><span class="nb">Index, </span><span class="o">+</span><span class="nb">Term, ?Argument</span><span class="o">)</span><span class="nb">}{HiLog}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{hilog</span><span class="nv">\_</span><span class="nb">arg</span><span class="o">/</span><span class="m">3</span><span class="nb">}}</span>
</div><div id="l1419" class="code_block"><span class="nb">    If {</span><span class="nv">\tt</span><span class="nb"> Term} is a Prolog term, it has the same behaviour as {</span><span class="nv">\tt</span><span class="nb"> arg</span><span class="o">/</span><span class="m">3</span><span class="nb">},</span>
</div><div id="l1420" class="code_block"><span class="nb">    but if {</span><span class="nv">\tt</span><span class="nb"> Term} is a proper HiLog term, {</span><span class="nv">\tt</span><span class="nb"> hilog</span><span class="nv">\_</span><span class="nb">arg</span><span class="o">/</span><span class="m">3</span><span class="nb">} unifies </span>
</div><div id="l1421" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> Argument} with the </span>
</div><div id="l1422" class="code_block"><span class="nb">    </span><span class="s">$</span>(<span class="nb">{</span><span class="k">\tt</span> Index<span class="nb">}</span>+1)<span class="nb">^{</span>th<span class="nb">}</span><span class="s">$</span><span class="nb"> argument of the Prolog representation of </span>
</div><div id="l1423" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> Term}</span><span class="nv">\@</span><span class="nb">.  Semantically, {</span><span class="nv">\tt</span><span class="nb"> Argument} is the </span><span class="s">$</span><span class="nb">{</span><span class="k">\tt</span> Index<span class="nb">}^{</span>th<span class="nb">}</span><span class="s">$</span><span class="nb"> </span>
</div><div id="l1424" class="code_block"><span class="nb">    argument to which the {</span><span class="nv">\em</span><span class="nb"> HiLog functor} of {</span><span class="nv">\tt</span><span class="nb"> Term} is applied.</span>
</div><div id="l1425" class="code_block"><span class="nb">    The arguments of the {</span><span class="nv">\tt</span><span class="nb"> Term} are numbered from~</span><span class="m">1</span><span class="nb"> upwards. An atomic term </span>
</div><div id="l1426" class="code_block"><span class="nb">    is taken to have </span><span class="s">$</span>0<span class="s">$</span><span class="nb"> arguments.  </span>
</div><div id="l1427" class="code_block"><span class="nb">    </span>
</div><div id="l1428" class="code_block"><span class="nb">    Initially, {</span><span class="nv">\tt</span><span class="nb"> Index} must be instantiated to a positive integer and </span>
</div><div id="l1429" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> Term} to any non</span><span class="o">-</span><span class="nb">variable Prolog or HiLog term.</span>
</div><div id="l1430" class="code_block"><span class="nb">    If the initial conditions are not satisfied or~</span><span class="s">$</span>I<span class="s">$</span><span class="nb"> is </span>
</div><div id="l1431" class="code_block"><span class="nb">    out of range, the call quietly fails. Note that like {</span><span class="nv">\tt</span><span class="nb"> arg</span><span class="o">/</span><span class="m">3</span><span class="nb">}</span>
</div><div id="l1432" class="code_block"><span class="nb">    this predicate does not succeed for {</span><span class="nv">\tt</span><span class="nb"> Index}</span><span class="o">=</span><span class="m">0</span><span class="nb">.</span>
</div><div id="l1433" class="code_block">
</div><div id="l1434" class="code_block"><span class="nb">    Examples:</span>
</div><div id="l1435" class="code_block"><span class="nb">    {</span><span class="nv">\footnotesize</span>
</div><div id="l1436" class="code_block"><span class="nb">     </span><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l1437" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> hilog_arg</span><span class="o">(</span><span class="m">2</span><span class="nb">, p</span><span class="o">(</span><span class="nb">a,b</span><span class="o">)</span><span class="nb">, A</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1438" class="code_block"><span class="nb">                   A </span><span class="o">=</span><span class="nb"> b</span>
</div><div id="l1439" class="code_block">
</div><div id="l1440" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> hilog_arg</span><span class="o">(</span><span class="m">2</span><span class="nb">, h</span><span class="o">(</span><span class="nb">a,b</span><span class="o">)</span><span class="nb">, A</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1441" class="code_block"><span class="nb">                   A </span><span class="o">=</span><span class="nb"> b</span>
</div><div id="l1442" class="code_block">
</div><div id="l1443" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> hilog_arg</span><span class="o">(</span><span class="m">3</span><span class="nb">, X</span><span class="o">(</span><span class="nb">a,b,c</span><span class="o">)</span><span class="nb">, A</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1444" class="code_block"><span class="nb">                   X </span><span class="o">=</span><span class="nb"> _</span><span class="m">595820</span>
</div><div id="l1445" class="code_block"><span class="nb">                   A </span><span class="o">=</span><span class="nb"> c</span>
</div><div id="l1446" class="code_block">
</div><div id="l1447" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> hilog_arg</span><span class="o">(</span><span class="m">1</span><span class="nb">, map</span><span class="o">(</span><span class="nb">f</span><span class="o">)(</span><span class="nb">a,b</span><span class="o">)</span><span class="nb">, A</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1448" class="code_block"><span class="nb">                   A </span><span class="o">=</span><span class="nb"> a</span>
</div><div id="l1449" class="code_block">
</div><div id="l1450" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> hilog_arg</span><span class="o">(</span><span class="m">2</span><span class="nb">, map</span><span class="o">(</span><span class="nb">f</span><span class="o">)(</span><span class="nb">a,b</span><span class="o">)</span><span class="nb">, A</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1451" class="code_block"><span class="nb">                   A </span><span class="o">=</span><span class="nb"> b</span>
</div><div id="l1452" class="code_block">
</div><div id="l1453" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> hilog_arg</span><span class="o">(</span><span class="m">1</span><span class="nb">, </span><span class="o">(</span><span class="nb">a</span><span class="o">+</span><span class="nb">b</span><span class="o">)(</span><span class="nb">foo,bar</span><span class="o">)</span><span class="nb">, A</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1454" class="code_block"><span class="nb">                   A </span><span class="o">=</span><span class="nb"> foo</span>
</div><div id="l1455" class="code_block">
</div><div id="l1456" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> hilog_arg</span><span class="o">(</span><span class="m">1</span><span class="nb">, apply</span><span class="o">(</span><span class="nb">foo</span><span class="o">)</span><span class="nb">, A</span><span class="o">)</span><span class="nb">. </span>
</div><div id="l1457" class="code_block"><span class="nb">                   A </span><span class="o">=</span><span class="nb"> foo</span>
</div><div id="l1458" class="code_block">
</div><div id="l1459" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> hilog_arg</span><span class="o">(</span><span class="m">1</span><span class="nb">, apply</span><span class="o">(</span><span class="nb">foo,bar</span><span class="o">)</span><span class="nb">, A</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1460" class="code_block"><span class="nb">                   A </span><span class="o">=</span><span class="nb"> bar</span>
</div><div id="l1461" class="code_block"><span class="nb">     </span><span class="nv">\end</span><span class="nb">{verbatim}}</span>
</div><div id="l1462" class="code_block">
</div><div id="l1463" class="code_block"><span class="nb">    Note the difference between the last two examples. The difference is </span>
</div><div id="l1464" class="code_block"><span class="nb">    due to the fact that {</span><span class="nv">\tt</span><span class="nb"> apply</span><span class="o">/</span><span class="m">1</span><span class="nb">} is a Prolog term, while </span>
</div><div id="l1465" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> apply</span><span class="o">/</span><span class="m">2</span><span class="nb">} is a proper HiLog term.</span>
</div><div id="l1466" class="code_block">
</div><div id="l1467" class="code_block"><span class="nv">\ouritem</span><span class="nb">{?Term </span><span class="o">=</span><span class="nb">.. </span><span class="o">[</span><span class="nb">?Functor |?ArgList</span><span class="o">]</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{</span><span class="o">=</span><span class="nb">..</span><span class="o">/</span><span class="m">2</span><span class="nb">}} </span>
</div><div id="l1468" class="code_block"><span class="nb">    Succeeds when {</span><span class="nv">\tt</span><span class="nb"> Term} is any </span><span class="o">(</span><span class="nb">Prolog or</span><span class="o">)</span><span class="nb"> HiLog term, {</span><span class="nv">\tt</span><span class="nb"> Functor} is </span>
</div><div id="l1469" class="code_block"><span class="nb">    its Prolog functor and {</span><span class="nv">\tt</span><span class="nb"> ArgList} is the list of its arguments. </span>
</div><div id="l1470" class="code_block"><span class="nb">    The use of {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">=</span><span class="nb">..</span><span class="o">/</span><span class="m">2</span><span class="nb">} </span><span class="o">(</span><span class="nb">pronounced {</span><span class="nv">\em</span><span class="nb"> univ}</span><span class="o">)</span><span class="nb"> although convenient, </span>
</div><div id="l1471" class="code_block"><span class="nb">    can nearly always be avoided.</span>
</div><div id="l1472" class="code_block"><span class="nb">    Whenever efficiency is critical, it is advisable to use the</span>
</div><div id="l1473" class="code_block"><span class="nb">    predicates {</span><span class="nv">\tt</span><span class="nb"> functor</span><span class="o">/</span><span class="m">3</span><span class="nb">} and {</span><span class="nv">\tt</span><span class="nb"> arg</span><span class="o">/</span><span class="m">3</span><span class="nb">}, since {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">=</span><span class="nb">..</span><span class="o">/</span><span class="m">2</span><span class="nb">} is </span>
</div><div id="l1474" class="code_block"><span class="nb">    implemented by calls to these predicates.  The behaviour of </span>
</div><div id="l1475" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">=</span><span class="nb">..</span><span class="o">/</span><span class="m">2</span><span class="nb">} is as follows:</span>
</div><div id="l1476" class="code_block"><span class="nb">    </span><span class="nv">\begin</span><span class="nb">{itemize}</span>
</div><div id="l1477" class="code_block"><span class="nb">    </span><span class="nv">\item</span><span class="nb"> If initially {</span><span class="nv">\tt</span><span class="nb"> Term} is uninstantiated, then the list in the </span>
</div><div id="l1478" class="code_block"><span class="nb">          second argument of {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">=</span><span class="nb">..</span><span class="o">/</span><span class="m">2</span><span class="nb">} must be instantiated either to a</span>
</div><div id="l1479" class="code_block"><span class="nb">          {</span><span class="nv">\em</span><span class="nb"> proper list} </span><span class="o">(</span><span class="nb">list of determinate length</span><span class="o">)</span><span class="nb"> whose head is an </span>
</div><div id="l1480" class="code_block"><span class="nb">          atom, or to a list of length </span><span class="m">1</span><span class="nb"> whose head is a number.</span>
</div><div id="l1481" class="code_block"><span class="nb">    </span><span class="nv">\item</span><span class="nb"> If the arguments of {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">=</span><span class="nb">..</span><span class="o">/</span><span class="m">2</span><span class="nb">} are both uninstantiated, or if </span>
</div><div id="l1482" class="code_block"><span class="nb">          either of them is not what is expected, {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">=</span><span class="nb">..</span><span class="o">/</span><span class="m">2</span><span class="nb">} aborts, </span>
</div><div id="l1483" class="code_block"><span class="nb">          producing an appropriate error message.</span>
</div><div id="l1484" class="code_block"><span class="nb">    </span><span class="nv">\end</span><span class="nb">{itemize}</span>
</div><div id="l1485" class="code_block">
</div><div id="l1486" class="code_block"><span class="nb">    Examples:</span>
</div><div id="l1487" class="code_block"><span class="nb">    {</span><span class="nv">\footnotesize</span>
</div><div id="l1488" class="code_block"><span class="nb">     </span><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l1489" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> X </span><span class="o">-</span><span class="nb"> </span><span class="m">1</span><span class="nb"> </span><span class="o">=</span><span class="nb">.. L.</span>
</div><div id="l1490" class="code_block"><span class="nb">                   X </span><span class="o">=</span><span class="nb"> _</span><span class="m">595692</span>
</div><div id="l1491" class="code_block"><span class="nb">                   L </span><span class="o">=</span><span class="nb"> </span><span class="o">[-</span><span class="nb">,_</span><span class="m">595692</span><span class="nb">,</span><span class="m">1</span><span class="o">]</span>
</div><div id="l1492" class="code_block">
</div><div id="l1493" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> p</span><span class="o">(</span><span class="nb">a,b,c</span><span class="o">)</span><span class="nb"> </span><span class="o">=</span><span class="nb">.. L.</span>
</div><div id="l1494" class="code_block"><span class="nb">                   L </span><span class="o">=</span><span class="nb"> </span><span class="o">[</span><span class="nb">p,a,b,c</span><span class="o">]</span>
</div><div id="l1495" class="code_block">
</div><div id="l1496" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> h</span><span class="o">(</span><span class="nb">a,b,c</span><span class="o">)</span><span class="nb"> </span><span class="o">=</span><span class="nb">.. L.</span>
</div><div id="l1497" class="code_block"><span class="nb">                   L </span><span class="o">=</span><span class="nb"> </span><span class="o">[</span><span class="nb">apply,h,a,b,c</span><span class="o">]</span>
</div><div id="l1498" class="code_block">
</div><div id="l1499" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> map</span><span class="o">(</span><span class="nb">p</span><span class="o">)(</span><span class="nb">a,b</span><span class="o">)</span><span class="nb"> </span><span class="o">=</span><span class="nb">.. L.</span>
</div><div id="l1500" class="code_block"><span class="nb">                   L </span><span class="o">=</span><span class="nb"> </span><span class="o">[</span><span class="nb">apply,map</span><span class="o">(</span><span class="nb">p</span><span class="o">)</span><span class="nb">,a,b</span><span class="o">]</span>
</div><div id="l1501" class="code_block">
</div><div id="l1502" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> T </span><span class="o">=</span><span class="nb">.. </span><span class="o">[</span><span class="nb">foo</span><span class="o">]</span><span class="nb">.</span>
</div><div id="l1503" class="code_block"><span class="nb">                   T </span><span class="o">=</span><span class="nb"> foo</span>
</div><div id="l1504" class="code_block">
</div><div id="l1505" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> T </span><span class="o">=</span><span class="nb">.. </span><span class="o">[</span><span class="m">3</span><span class="nb">|X</span><span class="o">]</span><span class="nb">.</span>
</div><div id="l1506" class="code_block"><span class="nb">                   T </span><span class="o">=</span><span class="nb"> </span><span class="m">3</span>
</div><div id="l1507" class="code_block"><span class="nb">                   X </span><span class="o">=</span><span class="nb"> </span><span class="o">[]</span>
</div><div id="l1508" class="code_block">
</div><div id="l1509" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> T </span><span class="o">=</span><span class="nb">.. </span><span class="o">[</span><span class="nb">apply,X,a,b</span><span class="o">]</span><span class="nb">.</span>
</div><div id="l1510" class="code_block"><span class="nb">                   T </span><span class="o">=</span><span class="nb"> apply</span><span class="o">(</span><span class="nb">X,a,b</span><span class="o">)</span>
</div><div id="l1511" class="code_block">
</div><div id="l1512" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> T </span><span class="o">=</span><span class="nb">.. </span><span class="o">[</span><span class="m">1</span><span class="nb">,</span><span class="m">2</span><span class="o">]</span><span class="nb">.</span>
</div><div id="l1513" class="code_block"><span class="nb">                   </span><span class="o">++</span><span class="nb">Error: Wrong type</span><span class="o">(</span><span class="nb">s</span><span class="o">)</span><span class="nb"> in argument </span><span class="m">2</span><span class="nb"> of </span><span class="o">=</span><span class="nb">..</span><span class="o">/</span><span class="m">2</span>
</div><div id="l1514" class="code_block"><span class="nb">                   Aborting...</span>
</div><div id="l1515" class="code_block">
</div><div id="l1516" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> T </span><span class="o">=</span><span class="nb">.. </span><span class="o">[</span><span class="nb">a</span><span class="o">+</span><span class="nb">b,</span><span class="m">2</span><span class="o">]</span><span class="nb">.</span>
</div><div id="l1517" class="code_block"><span class="nb">                   </span><span class="o">++</span><span class="nb">Error: Wrong type</span><span class="o">(</span><span class="nb">s</span><span class="o">)</span><span class="nb"> in argument </span><span class="m">2</span><span class="nb"> of </span><span class="o">=</span><span class="nb">..</span><span class="o">/</span><span class="m">2</span>
</div><div id="l1518" class="code_block"><span class="nb">                   Aborting..</span>
</div><div id="l1519" class="code_block">
</div><div id="l1520" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> X </span><span class="o">=</span><span class="nb">.. </span><span class="o">[</span><span class="nb">foo|Y</span><span class="o">]</span><span class="nb">.</span>
</div><div id="l1521" class="code_block"><span class="nb">                   </span><span class="o">++</span><span class="nb">Error: Argument </span><span class="m">2</span><span class="nb"> of </span><span class="o">=</span><span class="nb">..</span><span class="o">/</span><span class="m">2</span><span class="nb"> is not a proper list</span>
</div><div id="l1522" class="code_block"><span class="nb">                   Aborting...</span>
</div><div id="l1523" class="code_block"><span class="nb">     </span><span class="nv">\end</span><span class="nb">{verbatim}}</span>
</div><div id="l1524" class="code_block">
</div><div id="l1525" class="code_block"><span class="nb">     Exceptions:</span>
</div><div id="l1526" class="code_block"><span class="nb">     </span><span class="nv">\begin</span><span class="nb">{description}</span>
</div><div id="l1527" class="code_block"><span class="nb">     </span><span class="nv">\item</span><span class="o">[</span><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> instantiation</span><span class="nv">\_</span><span class="nb">error}</span><span class="o">]</span>
</div><div id="l1528" class="code_block"><span class="nb">	Argument </span><span class="m">2</span><span class="nb"> of {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">=</span><span class="nb">..</span><span class="o">/</span><span class="m">2</span><span class="nb">} is not a proper list.</span>
</div><div id="l1529" class="code_block"><span class="nb">     </span><span class="nv">\item</span><span class="o">[</span><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> type</span><span class="nv">\_</span><span class="nb">error}</span><span class="o">]</span>
</div><div id="l1530" class="code_block"><span class="nb">	Head of argument </span><span class="m">2</span><span class="nb"> of {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">=</span><span class="nb">..</span><span class="o">/</span><span class="m">2</span><span class="nb">} is not an atom or number.</span>
</div><div id="l1531" class="code_block"><span class="nb">     </span><span class="nv">\end</span><span class="nb">{description}</span>
</div><div id="l1532" class="code_block">
</div><div id="l1533" class="code_block"><span class="c">%in the following line I used a very ``dirty&#39;&#39; LaTeX hack! -- Kostis.</span>
</div><div id="l1534" class="code_block">
</div><div id="l1535" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{?Term </span><span class="nv">\^</span><span class="nb">{ }</span><span class="o">=</span><span class="nb">.. </span><span class="o">[</span><span class="nb">?F |?ArgList</span><span class="o">]</span><span class="nb">}{HiLog}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{</span><span class="nv">\^</span><span class="nb">{ }</span><span class="o">=</span><span class="nb">..</span><span class="o">/</span><span class="m">2</span><span class="nb">}} </span>
</div><div id="l1536" class="code_block"><span class="nb">    When {</span><span class="nv">\tt</span><span class="nb"> Term} is a Prolog term, this predicate behaves exactly like</span>
</div><div id="l1537" class="code_block"><span class="nb">    the Prolog {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">=</span><span class="nb">..</span><span class="o">/</span><span class="m">2</span><span class="nb">}. However when {</span><span class="nv">\tt</span><span class="nb"> Term} is a proper HiLog term, </span>
</div><div id="l1538" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> </span><span class="nv">\verb</span><span class="nb">|^|</span><span class="o">=</span><span class="nb">..</span><span class="o">/</span><span class="m">2</span><span class="nb">} </span>
</div><div id="l1539" class="code_block"><span class="nb">    succeeds unifying {</span><span class="nv">\tt</span><span class="nb"> F} to its HiLog functor and {</span><span class="nv">\tt</span><span class="nb"> ArgList} to the </span>
</div><div id="l1540" class="code_block"><span class="nb">    list of the arguments to which this HiLog functor is applied. Like </span>
</div><div id="l1541" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">=</span><span class="nb">..</span><span class="o">/</span><span class="m">2</span><span class="nb">}, the use of {</span><span class="nv">\tt</span><span class="nb"> </span><span class="nv">\verb</span><span class="nb">|^|</span><span class="o">=</span><span class="nb">..</span><span class="o">/</span><span class="m">2</span><span class="nb">} can nearly always be avoided</span>
</div><div id="l1542" class="code_block"><span class="nb">    by using the more efficient predicates {</span><span class="nv">\tt</span><span class="nb"> hilog</span><span class="nv">\_</span><span class="nb">functor</span><span class="o">/</span><span class="m">3</span><span class="nb">} and </span>
</div><div id="l1543" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> hilog</span><span class="nv">\_</span><span class="nb">arg</span><span class="o">/</span><span class="m">3</span><span class="nb">}. The behaviour of {</span><span class="nv">\tt</span><span class="nb"> </span><span class="nv">\verb</span><span class="nb">|^|</span><span class="o">=</span><span class="nb">..</span><span class="o">/</span><span class="m">2</span><span class="nb">}, on HiLog terms </span>
</div><div id="l1544" class="code_block"><span class="nb">    is as follows:</span>
</div><div id="l1545" class="code_block"><span class="nb">    </span><span class="nv">\begin</span><span class="nb">{itemize}</span>
</div><div id="l1546" class="code_block"><span class="nb">    </span><span class="nv">\item</span><span class="nb"> If initially {</span><span class="nv">\tt</span><span class="nb"> Term} is uninstantiated, then the list in the </span>
</div><div id="l1547" class="code_block"><span class="nb">          second argument of {</span><span class="nv">\tt</span><span class="nb"> </span><span class="nv">\verb</span><span class="nb">|^|</span><span class="o">=</span><span class="nb">..</span><span class="o">/</span><span class="m">2</span><span class="nb">} must be instantiated to </span>
</div><div id="l1548" class="code_block"><span class="nb">          a {</span><span class="nv">\em</span><span class="nb"> proper list} </span><span class="o">(</span><span class="nb">list of determinate length</span><span class="o">)</span><span class="nb"> whose head can </span>
</div><div id="l1549" class="code_block"><span class="nb">          be any Prolog or HiLog term.</span>
</div><div id="l1550" class="code_block"><span class="nb">    </span><span class="nv">\item</span><span class="nb"> If the arguments of {</span><span class="nv">\tt</span><span class="nb"> </span><span class="nv">\verb</span><span class="nb">|^|</span><span class="o">=</span><span class="nb">..</span><span class="o">/</span><span class="m">2</span><span class="nb">} are both uninstantiated, </span>
</div><div id="l1551" class="code_block"><span class="nb">          or if the second of them is not what is expected, </span>
</div><div id="l1552" class="code_block"><span class="nb">          {</span><span class="nv">\tt</span><span class="nb"> </span><span class="nv">\verb</span><span class="nb">|^|</span><span class="o">=</span><span class="nb">..</span><span class="o">/</span><span class="m">2</span><span class="nb">} aborts, producing an appropriate error message.</span>
</div><div id="l1553" class="code_block"><span class="nb">    </span><span class="nv">\end</span><span class="nb">{itemize}</span>
</div><div id="l1554" class="code_block"><span class="nb">    Examples:</span>
</div><div id="l1555" class="code_block"><span class="nb">    {</span><span class="nv">\footnotesize</span>
</div><div id="l1556" class="code_block"><span class="nb">     </span><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l1557" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> p</span><span class="o">(</span><span class="nb">a,b,c</span><span class="o">)</span><span class="nb"> ^</span><span class="o">=</span><span class="nb">.. L.</span>
</div><div id="l1558" class="code_block"><span class="nb">                   L </span><span class="o">=</span><span class="nb"> </span><span class="o">[</span><span class="nb">p,a,b,c</span><span class="o">]</span>
</div><div id="l1559" class="code_block">
</div><div id="l1560" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> h</span><span class="o">(</span><span class="nb">a,b,c</span><span class="o">)</span><span class="nb"> ^</span><span class="o">=</span><span class="nb">.. L.</span>
</div><div id="l1561" class="code_block"><span class="nb">                   L </span><span class="o">=</span><span class="nb"> </span><span class="o">[</span><span class="nb">h,a,b,c</span><span class="o">]</span>
</div><div id="l1562" class="code_block">
</div><div id="l1563" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> map</span><span class="o">(</span><span class="nb">p</span><span class="o">)(</span><span class="nb">a,b</span><span class="o">)</span><span class="nb"> ^</span><span class="o">=</span><span class="nb">.. L.</span>
</div><div id="l1564" class="code_block"><span class="nb">                   L </span><span class="o">=</span><span class="nb"> </span><span class="o">[</span><span class="nb">map</span><span class="o">(</span><span class="nb">p</span><span class="o">)</span><span class="nb">,a,b</span><span class="o">]</span>
</div><div id="l1565" class="code_block">
</div><div id="l1566" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> T ^</span><span class="o">=</span><span class="nb">.. </span><span class="o">[</span><span class="nb">X,a,b</span><span class="o">]</span><span class="nb">.</span>
</div><div id="l1567" class="code_block"><span class="nb">                   T </span><span class="o">=</span><span class="nb"> apply</span><span class="o">(</span><span class="nb">X,a,b</span><span class="o">)</span>
</div><div id="l1568" class="code_block">
</div><div id="l1569" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> T ^</span><span class="o">=</span><span class="nb">.. </span><span class="o">[</span><span class="m">2</span><span class="nb">,</span><span class="m">2</span><span class="o">]</span><span class="nb">.</span>
</div><div id="l1570" class="code_block"><span class="nb">                   T </span><span class="o">=</span><span class="nb"> apply</span><span class="o">(</span><span class="m">2</span><span class="nb">,</span><span class="m">2</span><span class="o">)</span>
</div><div id="l1571" class="code_block">
</div><div id="l1572" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> T ^</span><span class="o">=</span><span class="nb">.. </span><span class="o">[</span><span class="nb">a</span><span class="o">+</span><span class="nb">b,</span><span class="m">2</span><span class="o">]</span><span class="nb">.</span>
</div><div id="l1573" class="code_block"><span class="nb">                   T </span><span class="o">=</span><span class="nb"> apply</span><span class="o">(</span><span class="nb">a</span><span class="o">+</span><span class="nb">b,</span><span class="m">2</span><span class="o">)</span>
</div><div id="l1574" class="code_block">
</div><div id="l1575" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> T ^</span><span class="o">=</span><span class="nb">.. </span><span class="o">[</span><span class="m">3</span><span class="nb">|X</span><span class="o">]</span><span class="nb">.</span>
</div><div id="l1576" class="code_block"><span class="nb">                   </span><span class="o">++</span><span class="nb">Error: Argument </span><span class="m">2</span><span class="nb"> of ^</span><span class="o">=</span><span class="nb">..</span><span class="o">/</span><span class="m">2</span><span class="nb"> is not a proper list</span>
</div><div id="l1577" class="code_block"><span class="nb">                   Aborting...</span>
</div><div id="l1578" class="code_block"><span class="nb">     </span><span class="nv">\end</span><span class="nb">{verbatim}}</span>
</div><div id="l1579" class="code_block">
</div><div id="l1580" class="code_block"><span class="nb">     Exceptions:</span>
</div><div id="l1581" class="code_block"><span class="nb">     </span><span class="nv">\begin</span><span class="nb">{description}</span>
</div><div id="l1582" class="code_block"><span class="nb">     </span><span class="nv">\item</span><span class="o">[</span><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> instantiation</span><span class="nv">\_</span><span class="nb">error}</span><span class="o">]</span>
</div><div id="l1583" class="code_block"><span class="nb">	Argument </span><span class="m">2</span><span class="nb"> of {</span><span class="nv">\tt</span><span class="nb"> </span><span class="nv">\verb</span><span class="nb">|^|</span><span class="o">=</span><span class="nb">..</span><span class="o">/</span><span class="m">2</span><span class="nb">} is not a proper list.</span>
</div><div id="l1584" class="code_block"><span class="nb">     </span><span class="nv">\end</span><span class="nb">{description}</span>
</div><div id="l1585" class="code_block">
</div><div id="l1586" class="code_block"><span class="nv">\ouritem</span><span class="nb">{copy</span><span class="nv">\_</span><span class="nb">term</span><span class="o">(+</span><span class="nb">Term, </span><span class="o">-</span><span class="nb">Copy</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{copy</span><span class="nv">\_</span><span class="nb">term</span><span class="o">/</span><span class="m">2</span><span class="nb">}}</span>
</div><div id="l1587" class="code_block"><span class="nb">    Makes a {</span><span class="nv">\tt</span><span class="nb"> Copy} of {</span><span class="nv">\tt</span><span class="nb"> Term} in which all variables have been</span>
</div><div id="l1588" class="code_block"><span class="nb">    replaced by brand new variables which occur nowhere else. It can</span>
</div><div id="l1589" class="code_block"><span class="nb">    be very handy when writing </span><span class="o">(</span><span class="nb">meta</span><span class="o">-)</span><span class="nb">interpreters for logic</span><span class="o">-</span><span class="nb">based</span>
</div><div id="l1590" class="code_block"><span class="nb">    languages.  The version of {</span><span class="nv">\tt</span><span class="nb"> copy</span><span class="nv">\_</span><span class="nb">term</span><span class="o">/</span><span class="m">2</span><span class="nb">} provided is {</span><span class="nv">\em</span><span class="nb"> space</span>
</div><div id="l1591" class="code_block"><span class="nb">    efficient} in the sense that it never copies ground terms. </span>
</div><div id="l1592" class="code_block"><span class="nb">    Predicate {</span><span class="nv">\tt</span><span class="nb"> copy</span><span class="nv">\_</span><span class="nb">term</span><span class="o">/</span><span class="m">2</span><span class="nb">} has no associated errors or exceptions.</span>
</div><div id="l1593" class="code_block">
</div><div id="l1594" class="code_block"><span class="nb">    Examples:</span>
</div><div id="l1595" class="code_block"><span class="nb">    {</span><span class="nv">\footnotesize</span>
</div><div id="l1596" class="code_block"><span class="nb">     </span><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l1597" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> copy_term</span><span class="o">(</span><span class="nb">X, Y</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1598" class="code_block">
</div><div id="l1599" class="code_block"><span class="nb">                   X </span><span class="o">=</span><span class="nb"> _</span><span class="m">598948</span>
</div><div id="l1600" class="code_block"><span class="nb">                   Y </span><span class="o">=</span><span class="nb"> _</span><span class="m">598904</span>
</div><div id="l1601" class="code_block">
</div><div id="l1602" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> copy_term</span><span class="o">(</span><span class="nb">f</span><span class="o">(</span><span class="nb">a,X</span><span class="o">)</span><span class="nb">, Y</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1603" class="code_block">
</div><div id="l1604" class="code_block"><span class="nb">                   X </span><span class="o">=</span><span class="nb"> _</span><span class="m">598892</span>
</div><div id="l1605" class="code_block"><span class="nb">                   Y </span><span class="o">=</span><span class="nb"> f</span><span class="o">(</span><span class="nb">a,_</span><span class="m">599112</span><span class="o">)</span>
</div><div id="l1606" class="code_block"><span class="nb">     </span><span class="nv">\end</span><span class="nb">{verbatim}}</span>
</div><div id="l1607" class="code_block">
</div><div id="l1608" class="code_block"><span class="nv">\end</span><span class="nb">{description}</span>
</div><div id="l1609" class="code_block">
</div><div id="l1610" class="code_block"><span class="nv">\subsection</span><span class="nb">{Atom Manipulation}</span>
</div><div id="l1611" class="code_block">
</div><div id="l1612" class="code_block"><span class="nv">\begin</span><span class="nb">{description}</span>
</div><div id="l1613" class="code_block">
</div><div id="l1614" class="code_block"><span class="nv">\ouritem</span><span class="nb">{name</span><span class="o">(</span><span class="nb">?Constant, ?CharList</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{name</span><span class="o">/</span><span class="m">2</span><span class="nb">}} </span>
</div><div id="l1615" class="code_block"><span class="nb">    The standard predicate {</span><span class="nv">\tt</span><span class="nb"> name</span><span class="o">/</span><span class="m">2</span><span class="nb">} performs the conversion </span>
</div><div id="l1616" class="code_block"><span class="nb">    between a constant and its character list representation. </span>
</div><div id="l1617" class="code_block"><span class="nb">    If {</span><span class="nv">\tt</span><span class="nb"> Constant} is supplied </span><span class="o">(</span><span class="nb">and is any atom or number</span><span class="o">)</span><span class="nb">, {</span><span class="nv">\tt</span><span class="nb"> CharList} </span>
</div><div id="l1618" class="code_block"><span class="nb">    is unified with a list of ASCII codes representing the {</span><span class="nv">\em</span><span class="nb"> ``name&#39;&#39;} </span>
</div><div id="l1619" class="code_block"><span class="nb">    of the constant.  In that case, {</span><span class="nv">\tt</span><span class="nb"> CharList} is exactly the list of </span>
</div><div id="l1620" class="code_block"><span class="nb">    ASCII character codes that appear in the printed representation of </span>
</div><div id="l1621" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> Constant}</span><span class="nv">\@</span><span class="nb">.  If on the other hand {</span><span class="nv">\tt</span><span class="nb"> Constant} is a variable, </span>
</div><div id="l1622" class="code_block"><span class="nb">    then {</span><span class="nv">\tt</span><span class="nb"> CharList} must be a proper list of ASCII character codes. </span>
</div><div id="l1623" class="code_block"><span class="nb">    In that case, {</span><span class="nv">\tt</span><span class="nb"> name</span><span class="o">/</span><span class="m">2</span><span class="nb">} will convert a list of ASCII characters </span>
</div><div id="l1624" class="code_block"><span class="nb">    that can represent a number to a number rather than to a character string.</span>
</div><div id="l1625" class="code_block"><span class="nb">    As a consequence of this, there are some atoms </span><span class="o">(</span><span class="nb">for example </span><span class="nv">\verb</span><span class="nb">|&#39;</span><span class="m">18</span><span class="nb">&#39;|</span><span class="o">)</span>
</div><div id="l1626" class="code_block"><span class="nb">    which cannot be constructed by using {</span><span class="nv">\tt</span><span class="nb"> name</span><span class="o">/</span><span class="m">2</span><span class="nb">}</span><span class="nv">\@</span><span class="nb">. </span>
</div><div id="l1627" class="code_block"><span class="nb">    If conversion to an atom is preferred in these cases, the </span>
</div><div id="l1628" class="code_block"><span class="nb">    standard predicate {</span><span class="nv">\tt</span><span class="nb"> atom</span><span class="nv">\_</span><span class="nb">codes</span><span class="o">/</span><span class="m">2</span><span class="nb">} should be used instead. The </span>
</div><div id="l1629" class="code_block"><span class="nb">    syntax for numbers that is accepted by {</span><span class="nv">\tt</span><span class="nb"> name</span><span class="o">/</span><span class="m">2</span><span class="nb">} is exactly the one </span>
</div><div id="l1630" class="code_block"><span class="nb">    which {</span><span class="nv">\tt</span><span class="nb"> read</span><span class="o">/</span><span class="m">1</span><span class="nb">} accepts.  Predicate {</span><span class="nv">\tt</span><span class="nb"> name</span><span class="o">/</span><span class="m">2</span><span class="nb">} is provided for </span>
</div><div id="l1631" class="code_block"><span class="nb">    backwards compatibility.  It is advisable that new programs use</span>
</div><div id="l1632" class="code_block"><span class="nb">    the predicates {</span><span class="nv">\tt</span><span class="nb"> atom</span><span class="nv">\_</span><span class="nb">codes</span><span class="o">/</span><span class="m">2</span><span class="nb">} and {</span><span class="nv">\tt</span><span class="nb"> number</span><span class="nv">\_</span><span class="nb">codes</span><span class="o">/</span><span class="m">2</span><span class="nb">} described</span>
</div><div id="l1633" class="code_block"><span class="nb">    below.</span>
</div><div id="l1634" class="code_block">
</div><div id="l1635" class="code_block"><span class="nb">    In </span><span class="nv">\version\</span><span class="nb"> predicate {</span><span class="nv">\tt</span><span class="nb"> name</span><span class="o">/</span><span class="m">2</span><span class="nb">} is not yet implemented for </span>
</div><div id="l1636" class="code_block"><span class="nb">    converting from a real number to its character list representation, </span>
</div><div id="l1637" class="code_block"><span class="nb">    and if the representation of a real is provided as {</span><span class="nv">\tt</span><span class="nb"> CharList}, </span>
</div><div id="l1638" class="code_block"><span class="nb">    it will be converted to an atom.</span>
</div><div id="l1639" class="code_block">
</div><div id="l1640" class="code_block"><span class="nb">    If both of the arguments of {</span><span class="nv">\tt</span><span class="nb"> name</span><span class="o">/</span><span class="m">2</span><span class="nb">} are uninstantiated or </span>
</div><div id="l1641" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> CharList} is not a proper list of ASCII characters, {</span><span class="nv">\tt</span><span class="nb"> name</span><span class="o">/</span><span class="m">2</span><span class="nb">} </span>
</div><div id="l1642" class="code_block"><span class="nb">    will abort and an error message will be sent to the standard error stream.</span>
</div><div id="l1643" class="code_block">
</div><div id="l1644" class="code_block"><span class="nb">    Examples:</span>
</div><div id="l1645" class="code_block"><span class="nb">    {</span><span class="nv">\footnotesize</span>
</div><div id="l1646" class="code_block"><span class="nb">     </span><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l1647" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> name</span><span class="o">(</span><span class="nb">&#39;Foo&#39;, L</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1648" class="code_block"><span class="nb">                   L </span><span class="o">=</span><span class="nb"> </span><span class="o">[</span><span class="m">70</span><span class="nb">,</span><span class="m">111</span><span class="nb">,</span><span class="m">111</span><span class="o">]</span>
</div><div id="l1649" class="code_block">
</div><div id="l1650" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> name</span><span class="o">([]</span><span class="nb">, L</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1651" class="code_block"><span class="nb">                   L </span><span class="o">=</span><span class="nb"> </span><span class="o">[</span><span class="m">91</span><span class="nb">,</span><span class="m">93</span><span class="o">]</span>
</div><div id="l1652" class="code_block">
</div><div id="l1653" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> name</span><span class="o">(</span><span class="m">431</span><span class="nb">, L</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1654" class="code_block"><span class="nb">                   L </span><span class="o">=</span><span class="nb"> </span><span class="o">[</span><span class="m">52</span><span class="nb">,</span><span class="m">51</span><span class="nb">,</span><span class="m">49</span><span class="o">]</span>
</div><div id="l1655" class="code_block">
</div><div id="l1656" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> name</span><span class="o">(</span><span class="nb">X, </span><span class="o">[</span><span class="m">102</span><span class="nb">,</span><span class="m">111</span><span class="nb">,</span><span class="m">111</span><span class="o">])</span><span class="nb">.</span>
</div><div id="l1657" class="code_block"><span class="nb">                   X </span><span class="o">=</span><span class="nb"> foo</span>
</div><div id="l1658" class="code_block"><span class="nb"> </span>
</div><div id="l1659" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> name</span><span class="o">(</span><span class="nb">X, </span><span class="o">[])</span><span class="nb">.</span>
</div><div id="l1660" class="code_block"><span class="nb">                   X </span><span class="o">=</span><span class="nb"> &#39;&#39;</span>
</div><div id="l1661" class="code_block">
</div><div id="l1662" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> name</span><span class="o">(</span><span class="nb">X, &quot;Foo&quot;</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1663" class="code_block"><span class="nb">                   X </span><span class="o">=</span><span class="nb"> &#39;Foo&#39;</span>
</div><div id="l1664" class="code_block">
</div><div id="l1665" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> name</span><span class="o">(</span><span class="nb">X, </span><span class="o">[</span><span class="m">52</span><span class="nb">,</span><span class="m">51</span><span class="nb">,</span><span class="m">49</span><span class="o">])</span><span class="nb">.</span>
</div><div id="l1666" class="code_block"><span class="nb">                   X </span><span class="o">=</span><span class="nb"> </span><span class="m">431</span>
</div><div id="l1667" class="code_block">
</div><div id="l1668" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> name</span><span class="o">(</span><span class="nb">X, </span><span class="o">[</span><span class="m">45</span><span class="nb">,</span><span class="m">48</span><span class="nb">,</span><span class="m">50</span><span class="nb">,</span><span class="m">49</span><span class="nb">,</span><span class="m">51</span><span class="o">])</span><span class="nb">, integer</span><span class="o">(</span><span class="nb">X</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1669" class="code_block"><span class="nb">                   X </span><span class="o">=</span><span class="nb"> </span><span class="o">-</span><span class="m">213</span>
</div><div id="l1670" class="code_block">
</div><div id="l1671" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> name</span><span class="o">(</span><span class="m">3</span><span class="nb">.</span><span class="m">14</span><span class="nb">, L</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1672" class="code_block"><span class="nb">                   </span><span class="o">++</span><span class="nb">Error: Predicate name</span><span class="o">/</span><span class="m">2</span><span class="nb"> for reals is not implemented yet</span>
</div><div id="l1673" class="code_block"><span class="nb">                   Aborting...</span>
</div><div id="l1674" class="code_block"><span class="nb">     </span><span class="nv">\end</span><span class="nb">{verbatim}}</span>
</div><div id="l1675" class="code_block">
</div><div id="l1676" class="code_block"><span class="nb">     Exceptions:</span>
</div><div id="l1677" class="code_block"><span class="nb">     </span><span class="nv">\begin</span><span class="nb">{description}</span>
</div><div id="l1678" class="code_block"><span class="nb">     </span><span class="nv">\item</span><span class="o">[</span><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> instantiation</span><span class="nv">\_</span><span class="nb">error}</span><span class="o">]</span>
</div><div id="l1679" class="code_block"><span class="nb">	Both arguments are uninstantiated, or argument </span><span class="m">2</span><span class="nb"> of {</span><span class="nv">\tt</span><span class="nb"> name</span><span class="o">/</span><span class="m">2</span><span class="nb">} </span>
</div><div id="l1680" class="code_block"><span class="nb">	contains a variable or is not a proper list.</span>
</div><div id="l1681" class="code_block"><span class="nb">     </span><span class="nv">\item</span><span class="o">[</span><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> type</span><span class="nv">\_</span><span class="nb">error}</span><span class="o">]</span>
</div><div id="l1682" class="code_block"><span class="nb">	{</span><span class="nv">\tt</span><span class="nb"> Constant} is not a variable, an atom or a number.</span>
</div><div id="l1683" class="code_block"><span class="nb">     </span><span class="nv">\item</span><span class="o">[</span><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> range</span><span class="nv">\_</span><span class="nb">error}</span><span class="o">]</span>
</div><div id="l1684" class="code_block"><span class="nb">	{</span><span class="nv">\tt</span><span class="nb"> CharList} is not a list of ASCII characters.</span>
</div><div id="l1685" class="code_block"><span class="nb">     </span><span class="nv">\item</span><span class="o">[</span><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> implementation</span><span class="nv">\_</span><span class="nb">error}</span><span class="o">]</span>
</div><div id="l1686" class="code_block"><span class="nb">	{</span><span class="nv">\tt</span><span class="nb"> Constant} is a real number </span><span class="o">(</span><span class="nb">conversion from a real to its </span>
</div><div id="l1687" class="code_block"><span class="nb">	character list representation is not implemented yet</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1688" class="code_block"><span class="nb">     </span><span class="nv">\end</span><span class="nb">{description}</span>
</div><div id="l1689" class="code_block">
</div><div id="l1690" class="code_block"><span class="nv">\ouritem</span><span class="nb">{atom</span><span class="nv">\_</span><span class="nb">codes</span><span class="o">(</span><span class="nb">?Atom, ?CharCodeList</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{atom</span><span class="nv">\_</span><span class="nb">codes</span><span class="o">/</span><span class="m">2</span><span class="nb">}} </span>
</div><div id="l1691" class="code_block"><span class="nb">    The standard predicate {</span><span class="nv">\tt</span><span class="nb"> atom</span><span class="nv">\_</span><span class="nb">codes</span><span class="o">/</span><span class="m">2</span><span class="nb">} performs the conversion </span>
</div><div id="l1692" class="code_block"><span class="nb">    between an atom and its character list representation. </span>
</div><div id="l1693" class="code_block"><span class="nb">    If {</span><span class="nv">\tt</span><span class="nb"> Atom} is supplied </span><span class="o">(</span><span class="nb">and is an atom</span><span class="o">)</span><span class="nb">, {</span><span class="nv">\tt</span><span class="nb"> CharList} </span>
</div><div id="l1694" class="code_block"><span class="nb">    is unified with a list of ASCII codes representing the {</span><span class="nv">\em</span><span class="nb"> ``name&#39;&#39;} </span>
</div><div id="l1695" class="code_block"><span class="nb">    of that atom.  In that case, {</span><span class="nv">\tt</span><span class="nb"> CharList} is exactly the list of </span>
</div><div id="l1696" class="code_block"><span class="nb">    ASCII character codes that appear in the printed representation of </span>
</div><div id="l1697" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> Atom}.  If on the other hand {</span><span class="nv">\tt</span><span class="nb"> Atom} is a variable, </span>
</div><div id="l1698" class="code_block"><span class="nb">    then {</span><span class="nv">\tt</span><span class="nb"> CharList} must be a proper list of ASCII character codes. </span>
</div><div id="l1699" class="code_block"><span class="nb">    In that case, {</span><span class="nv">\tt</span><span class="nb"> Atom} is instantiated to an atom containing</span>
</div><div id="l1700" class="code_block"><span class="nb">    exactly those characters, even if the characters look like the</span>
</div><div id="l1701" class="code_block"><span class="nb">    printed representation of a number.</span>
</div><div id="l1702" class="code_block">
</div><div id="l1703" class="code_block"><span class="nb">    If both of the arguments of {</span><span class="nv">\tt</span><span class="nb"> atom</span><span class="nv">\_</span><span class="nb">codes</span><span class="o">/</span><span class="m">2</span><span class="nb">} are uninstantiated or</span>
</div><div id="l1704" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> CharList} is not a proper list of ASCII characters, {</span><span class="nv">\tt</span>
</div><div id="l1705" class="code_block"><span class="nb">    atom</span><span class="nv">\_</span><span class="nb">codes</span><span class="o">/</span><span class="m">2</span><span class="nb">} aborts, and an error message will be sent to</span>
</div><div id="l1706" class="code_block"><span class="nb">    the standard error stream.</span>
</div><div id="l1707" class="code_block">
</div><div id="l1708" class="code_block"><span class="nb">    Examples:</span>
</div><div id="l1709" class="code_block"><span class="nb">    {</span><span class="nv">\footnotesize</span>
</div><div id="l1710" class="code_block"><span class="nb">     </span><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l1711" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> atom_codes</span><span class="o">(</span><span class="nb">&#39;Foo&#39;, L</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1712" class="code_block"><span class="nb">                   L </span><span class="o">=</span><span class="nb"> </span><span class="o">[</span><span class="m">70</span><span class="nb">,</span><span class="m">111</span><span class="nb">,</span><span class="m">111</span><span class="o">]</span>
</div><div id="l1713" class="code_block">
</div><div id="l1714" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> atom_codes</span><span class="o">([]</span><span class="nb">, L</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1715" class="code_block"><span class="nb">                   L </span><span class="o">=</span><span class="nb"> </span><span class="o">[</span><span class="m">91</span><span class="nb">,</span><span class="m">93</span><span class="o">]</span>
</div><div id="l1716" class="code_block">
</div><div id="l1717" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> atom_codes</span><span class="o">(</span><span class="nb">X, </span><span class="o">[</span><span class="m">102</span><span class="nb">,</span><span class="m">111</span><span class="nb">,</span><span class="m">111</span><span class="o">])</span><span class="nb">.</span>
</div><div id="l1718" class="code_block"><span class="nb">                   X </span><span class="o">=</span><span class="nb"> foo</span>
</div><div id="l1719" class="code_block"><span class="nb"> </span>
</div><div id="l1720" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> atom_codes</span><span class="o">(</span><span class="nb">X, </span><span class="o">[])</span><span class="nb">.</span>
</div><div id="l1721" class="code_block"><span class="nb">                   X </span><span class="o">=</span><span class="nb"> &#39;&#39;</span>
</div><div id="l1722" class="code_block">
</div><div id="l1723" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> atom_codes</span><span class="o">(</span><span class="nb">X, &quot;Foo&quot;</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1724" class="code_block"><span class="nb">                   X </span><span class="o">=</span><span class="nb"> &#39;Foo&#39;</span>
</div><div id="l1725" class="code_block">
</div><div id="l1726" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> atom_codes</span><span class="o">(</span><span class="nb">X, </span><span class="o">[</span><span class="m">52</span><span class="nb">,</span><span class="m">51</span><span class="nb">,</span><span class="m">49</span><span class="o">])</span><span class="nb">.</span>
</div><div id="l1727" class="code_block"><span class="nb">                   X </span><span class="o">=</span><span class="nb"> &#39;</span><span class="m">431</span><span class="nb">&#39;</span>
</div><div id="l1728" class="code_block">
</div><div id="l1729" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> atom_codes</span><span class="o">(</span><span class="nb">X, </span><span class="o">[</span><span class="m">52</span><span class="nb">,</span><span class="m">51</span><span class="nb">,</span><span class="m">49</span><span class="o">])</span><span class="nb">, integer</span><span class="o">(</span><span class="nb">X</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1730" class="code_block"><span class="nb">                   no</span>
</div><div id="l1731" class="code_block">
</div><div id="l1732" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> atom_codes</span><span class="o">(</span><span class="nb">X, </span><span class="o">[</span><span class="m">52</span><span class="nb">,Y,</span><span class="m">49</span><span class="o">])</span><span class="nb">.</span>
</div><div id="l1733" class="code_block"><span class="nb">                   </span><span class="o">!</span><span class="nb"> Instantiation error in argument </span><span class="m">2</span><span class="nb"> of atom_codes</span><span class="o">/</span><span class="m">2</span>
</div><div id="l1734" class="code_block"><span class="nb">                   </span><span class="o">!</span><span class="nb"> Aborting...</span>
</div><div id="l1735" class="code_block">
</div><div id="l1736" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> atom_codes</span><span class="o">(</span><span class="m">431</span><span class="nb">, L</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1737" class="code_block"><span class="nb">                   </span><span class="o">!</span><span class="nb"> Type error: in argument </span><span class="m">1</span><span class="nb"> of atom_codes</span><span class="o">/</span><span class="m">2</span>
</div><div id="l1738" class="code_block"><span class="nb">                   </span><span class="o">!</span><span class="nb"> atom expected, but something else found</span>
</div><div id="l1739" class="code_block"><span class="nb">                   </span><span class="o">!</span><span class="nb"> Aborting...</span>
</div><div id="l1740" class="code_block">
</div><div id="l1741" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> atom_codes</span><span class="o">(</span><span class="nb">X, </span><span class="o">[</span><span class="m">52</span><span class="nb">,</span><span class="m">300</span><span class="nb">,</span><span class="m">49</span><span class="o">])</span><span class="nb">.</span>
</div><div id="l1742" class="code_block"><span class="nb">                   </span><span class="o">!</span><span class="nb"> Range error: in argument </span><span class="m">2</span><span class="nb"> of atom_codes</span><span class="o">/</span><span class="m">2</span>
</div><div id="l1743" class="code_block"><span class="nb">                   </span><span class="o">!</span><span class="nb"> ASCII code expected, but </span><span class="m">300</span><span class="nb"> found</span>
</div><div id="l1744" class="code_block"><span class="nb">                   </span><span class="o">!</span><span class="nb"> Aborting...</span>
</div><div id="l1745" class="code_block"><span class="nb">     </span><span class="nv">\end</span><span class="nb">{verbatim}}</span>
</div><div id="l1746" class="code_block">
</div><div id="l1747" class="code_block"><span class="nb">    Exceptions:</span>
</div><div id="l1748" class="code_block"><span class="nb">    </span><span class="nv">\begin</span><span class="nb">{description}</span>
</div><div id="l1749" class="code_block"><span class="nb">    </span><span class="nv">\item</span><span class="o">[</span><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> instantiation</span><span class="nv">\_</span><span class="nb">error}</span><span class="o">]</span>
</div><div id="l1750" class="code_block"><span class="nb">	Both arguments are uninstantiated, or argument </span><span class="m">2</span>
</div><div id="l1751" class="code_block"><span class="nb">	is not a proper list, or it contains a variable.</span>
</div><div id="l1752" class="code_block"><span class="nb">    </span><span class="nv">\item</span><span class="o">[</span><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> type</span><span class="nv">\_</span><span class="nb">error}</span><span class="o">]</span>
</div><div id="l1753" class="code_block"><span class="nb">	{</span><span class="nv">\tt</span><span class="nb"> Atom} is not a variable or an atom.</span>
</div><div id="l1754" class="code_block"><span class="nb">    </span><span class="nv">\item</span><span class="o">[</span><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> range</span><span class="nv">\_</span><span class="nb">error}</span><span class="o">]</span>
</div><div id="l1755" class="code_block"><span class="nb">	{</span><span class="nv">\tt</span><span class="nb"> CharList} is not a list of ASCII characters.</span>
</div><div id="l1756" class="code_block"><span class="nb">    </span><span class="nv">\end</span><span class="nb">{description}</span>
</div><div id="l1757" class="code_block">
</div><div id="l1758" class="code_block"><span class="nv">\ouritem</span><span class="nb">{atom</span><span class="nv">\_</span><span class="nb">chars</span><span class="o">(</span><span class="nb">?Number, ?CharAtomList</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{atom</span><span class="nv">\_</span><span class="nb">chars</span><span class="o">/</span><span class="m">2</span><span class="nb">}} </span>
</div><div id="l1759" class="code_block"><span class="nb">    Like </span><span class="nv">\verb</span><span class="nb">|atom_codes|, but the list returned </span><span class="o">(</span><span class="nb">or input</span><span class="o">)</span><span class="nb"> is a list of</span>
</div><div id="l1760" class="code_block"><span class="nb">    characters </span><span class="nv">\emph</span><span class="nb">{as atoms} rather than ASCII codes. For instance, </span>
</div><div id="l1761" class="code_block"><span class="nb">    </span><span class="nv">\verb</span><span class="nb">|atom_chars</span><span class="o">(</span><span class="nb">abc,X</span><span class="o">)</span><span class="nb">| binds {</span><span class="nv">\tt</span><span class="nb"> X} to the list {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">[</span><span class="nb">a,b,c</span><span class="o">]</span><span class="nb">}</span>
</div><div id="l1762" class="code_block"><span class="nb">    instead of {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">[</span><span class="m">97</span><span class="nb">,</span><span class="m">98</span><span class="nb">,</span><span class="m">99</span><span class="o">]</span><span class="nb">}.</span>
</div><div id="l1763" class="code_block">
</div><div id="l1764" class="code_block"><span class="nv">\ouritem</span><span class="nb">{number</span><span class="nv">\_</span><span class="nb">codes</span><span class="o">(</span><span class="nb">?Number, ?CharCodeList</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{number</span><span class="nv">\_</span><span class="nb">codes</span><span class="o">/</span><span class="m">2</span><span class="nb">}} </span>
</div><div id="l1765" class="code_block"><span class="nb">    The standard predicate {</span><span class="nv">\tt</span><span class="nb"> number</span><span class="nv">\_</span><span class="nb">codes</span><span class="o">/</span><span class="m">2</span><span class="nb">} performs the conversion </span>
</div><div id="l1766" class="code_block"><span class="nb">    between a number and its character list representation. </span>
</div><div id="l1767" class="code_block"><span class="nb">    If {</span><span class="nv">\tt</span><span class="nb"> Number} is supplied </span><span class="o">(</span><span class="nb">and is a number</span><span class="o">)</span><span class="nb">, {</span><span class="nv">\tt</span><span class="nb"> CharList} is</span>
</div><div id="l1768" class="code_block"><span class="nb">    unified with a list of ASCII codes comprising the printed representation</span>
</div><div id="l1769" class="code_block"><span class="nb">    of that {</span><span class="nv">\tt</span><span class="nb"> Number}.  If on the other hand {</span><span class="nv">\tt</span><span class="nb"> Number} is a variable, </span>
</div><div id="l1770" class="code_block"><span class="nb">    then {</span><span class="nv">\tt</span><span class="nb"> CharList} must be a proper list of ASCII character codes that</span>
</div><div id="l1771" class="code_block"><span class="nb">    corresponds to the correct syntax of a number </span><span class="o">(</span><span class="nb">either integer or float</span><span class="o">)</span>
</div><div id="l1772" class="code_block"><span class="nb">    In that case, {</span><span class="nv">\tt</span><span class="nb"> Number} is instantiated to that number, otherwise</span>
</div><div id="l1773" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> number</span><span class="nv">\_</span><span class="nb">codes</span><span class="o">/</span><span class="m">2</span><span class="nb">} will simply fail.</span>
</div><div id="l1774" class="code_block">
</div><div id="l1775" class="code_block"><span class="nb">    If both of the arguments of {</span><span class="nv">\tt</span><span class="nb"> number</span><span class="nv">\_</span><span class="nb">codes</span><span class="o">/</span><span class="m">2</span><span class="nb">} are uninstantiated or</span>
</div><div id="l1776" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> CharList} is not a proper list of ASCII characters, {</span><span class="nv">\tt</span>
</div><div id="l1777" class="code_block"><span class="nb">    number</span><span class="nv">\_</span><span class="nb">codes</span><span class="o">/</span><span class="m">2</span><span class="nb">} aborts, and an error message will be sent to</span>
</div><div id="l1778" class="code_block"><span class="nb">    the standard error stream.</span>
</div><div id="l1779" class="code_block">
</div><div id="l1780" class="code_block"><span class="nb">    Examples:</span>
</div><div id="l1781" class="code_block"><span class="nb">    {</span><span class="nv">\footnotesize</span>
</div><div id="l1782" class="code_block"><span class="nb">     </span><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l1783" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> number_codes</span><span class="o">(</span><span class="m">123</span><span class="nb">, L</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1784" class="code_block"><span class="nb">                   L </span><span class="o">=</span><span class="nb"> </span><span class="o">[</span><span class="m">49</span><span class="nb">,</span><span class="m">50</span><span class="nb">,</span><span class="m">51</span><span class="o">]</span><span class="nb">;</span>
</div><div id="l1785" class="code_block">
</div><div id="l1786" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> number_codes</span><span class="o">(</span><span class="nb">N, </span><span class="o">[</span><span class="m">49</span><span class="nb">,</span><span class="m">50</span><span class="nb">,</span><span class="m">51</span><span class="o">])</span><span class="nb">, integer</span><span class="o">(</span><span class="nb">N</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1787" class="code_block"><span class="nb">                   N </span><span class="o">=</span><span class="nb"> </span><span class="m">123</span>
</div><div id="l1788" class="code_block">
</div><div id="l1789" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> number_codes</span><span class="o">(</span><span class="m">31</span><span class="nb">.</span><span class="m">4</span><span class="nb">e</span><span class="o">+</span><span class="m">10</span><span class="nb">, L</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1790" class="code_block"><span class="nb">                   L </span><span class="o">=</span><span class="nb"> </span><span class="o">[</span><span class="m">51</span><span class="nb">,</span><span class="m">46</span><span class="nb">,</span><span class="m">49</span><span class="nb">,</span><span class="m">51</span><span class="nb">,</span><span class="m">57</span><span class="nb">,</span><span class="m">57</span><span class="nb">,</span><span class="m">57</span><span class="nb">,</span><span class="m">55</span><span class="nb">,</span><span class="m">69</span><span class="nb">,</span><span class="m">43</span><span class="nb">,</span><span class="m">49</span><span class="nb">,</span><span class="m">48</span><span class="o">]</span>
</div><div id="l1791" class="code_block">
</div><div id="l1792" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> number_codes</span><span class="o">(</span><span class="nb">N, &quot;</span><span class="m">314</span><span class="nb">e</span><span class="o">+</span><span class="m">8</span><span class="nb">&quot;</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1793" class="code_block"><span class="nb">                   N </span><span class="o">=</span><span class="nb"> </span><span class="m">3</span><span class="nb">.</span><span class="m">14</span><span class="nb">e</span><span class="o">+</span><span class="m">10</span>
</div><div id="l1794" class="code_block">
</div><div id="l1795" class="code_block"><span class="nb">                   | ?</span><span class="o">-</span><span class="nb"> number_codes</span><span class="o">(</span><span class="nb">foo, L</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1796" class="code_block"><span class="nb">                   </span><span class="o">!</span><span class="nb"> Type error: in argument </span><span class="m">1</span><span class="nb"> of number_codes</span><span class="o">/</span><span class="m">2</span>
</div><div id="l1797" class="code_block"><span class="nb">                   </span><span class="o">!</span><span class="nb"> number expected, but something else found</span>
</div><div id="l1798" class="code_block"><span class="nb">                   </span><span class="o">!</span><span class="nb"> Aborting...</span>
</div><div id="l1799" class="code_block"><span class="nb">     </span><span class="nv">\end</span><span class="nb">{verbatim}}</span>
</div><div id="l1800" class="code_block">
</div><div id="l1801" class="code_block"><span class="nb">    Exceptions:</span>
</div><div id="l1802" class="code_block"><span class="nb">    </span><span class="nv">\begin</span><span class="nb">{description}</span>
</div><div id="l1803" class="code_block"><span class="nb">    </span><span class="nv">\item</span><span class="o">[</span><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> instantiation</span><span class="nv">\_</span><span class="nb">error}</span><span class="o">]</span>
</div><div id="l1804" class="code_block"><span class="nb">	Both arguments are uninstantiated, or argument </span><span class="m">2</span>
</div><div id="l1805" class="code_block"><span class="nb">	is not a proper list, or it contains a variable.</span>
</div><div id="l1806" class="code_block"><span class="nb">    </span><span class="nv">\item</span><span class="o">[</span><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> type</span><span class="nv">\_</span><span class="nb">error}</span><span class="o">]</span>
</div><div id="l1807" class="code_block"><span class="nb">	{</span><span class="nv">\tt</span><span class="nb"> Number} is not a variable or a number.</span>
</div><div id="l1808" class="code_block"><span class="nb">    </span><span class="nv">\item</span><span class="o">[</span><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> range</span><span class="nv">\_</span><span class="nb">error}</span><span class="o">]</span>
</div><div id="l1809" class="code_block"><span class="nb">	{</span><span class="nv">\tt</span><span class="nb"> CharList} is not a list of ASCII characters.</span>
</div><div id="l1810" class="code_block"><span class="nb">    </span><span class="nv">\end</span><span class="nb">{description}</span>
</div><div id="l1811" class="code_block">
</div><div id="l1812" class="code_block"><span class="nv">\ouritem</span><span class="nb">{number</span><span class="nv">\_</span><span class="nb">chars</span><span class="o">(</span><span class="nb">?Number, ?CharAtomList</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{number</span><span class="nv">\_</span><span class="nb">chars</span><span class="o">/</span><span class="m">2</span><span class="nb">}} </span>
</div><div id="l1813" class="code_block"><span class="nb">    Like </span><span class="nv">\verb</span><span class="nb">|number_codes|, but the list returned </span><span class="o">(</span><span class="nb">or input</span><span class="o">)</span><span class="nb"> is a list of</span>
</div><div id="l1814" class="code_block"><span class="nb">    characters </span><span class="nv">\emph</span><span class="nb">{as atoms} rather than ASCII codes. For instance, </span>
</div><div id="l1815" class="code_block"><span class="nb">    </span><span class="nv">\verb</span><span class="nb">|number_chars</span><span class="o">(</span><span class="m">123</span><span class="nb">,X</span><span class="o">)</span><span class="nb">| binds {</span><span class="nv">\tt</span><span class="nb"> X} to the list {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">[</span><span class="nb">&#39;</span><span class="m">1</span><span class="nb">&#39;,&#39;</span><span class="m">2</span><span class="nb">&#39;,&#39;</span><span class="m">3</span><span class="nb">&#39;</span><span class="o">]</span><span class="nb">}</span>
</div><div id="l1816" class="code_block"><span class="nb">    instead of {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">[</span><span class="m">49</span><span class="nb">,</span><span class="m">50</span><span class="nb">,</span><span class="m">51</span><span class="o">]</span><span class="nb">}.</span>
</div><div id="l1817" class="code_block">
</div><div id="l1818" class="code_block"><span class="nv">\ouritem</span><span class="nb">{number</span><span class="nv">\_</span><span class="nb">digits</span><span class="o">(</span><span class="nb">?Number, ?DigitList</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{number</span><span class="nv">\_</span><span class="nb">digits</span><span class="o">/</span><span class="m">2</span><span class="nb">}} </span>
</div><div id="l1819" class="code_block"><span class="nb">    Like </span><span class="nv">\verb</span><span class="nb">|number_chars|, but the list returned </span><span class="o">(</span><span class="nb">or input</span><span class="o">)</span><span class="nb"> is a list of</span>
</div><div id="l1820" class="code_block"><span class="nb">    digits </span><span class="nv">\emph</span><span class="nb">{as numbers} rather than ASCII codes </span><span class="o">(</span><span class="nb">for floats, the atom</span>
</div><div id="l1821" class="code_block"><span class="nb">    &#39;.&#39;, &#39;</span><span class="o">+</span><span class="nb">&#39; or &#39;</span><span class="o">-</span><span class="nb">&#39;, and &#39;e&#39; will also be present in the list</span><span class="o">)</span><span class="nb">. For instance, </span>
</div><div id="l1822" class="code_block"><span class="nb">    </span><span class="nv">\verb</span><span class="nb">|number_digits</span><span class="o">(</span><span class="m">123</span><span class="nb">,X</span><span class="o">)</span><span class="nb">| binds {</span><span class="nv">\tt</span><span class="nb"> X} to the list {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">[</span><span class="m">1</span><span class="nb">,</span><span class="m">2</span><span class="nb">,</span><span class="m">3</span><span class="o">]</span><span class="nb">}</span>
</div><div id="l1823" class="code_block"><span class="nb">    instead of {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">[</span><span class="nb">&#39;</span><span class="m">1</span><span class="nb">&#39;,&#39;</span><span class="m">2</span><span class="nb">&#39;,&#39;</span><span class="m">3</span><span class="nb">&#39;</span><span class="o">]</span><span class="nb">}, and </span><span class="nv">\verb</span><span class="nb">|number_digits</span><span class="o">(</span><span class="m">123</span><span class="nb">.</span><span class="m">45</span><span class="nb">,X</span><span class="o">)</span><span class="nb">|</span>
</div><div id="l1824" class="code_block"><span class="nb">    binds {</span><span class="nv">\tt</span><span class="nb"> X} to {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">[</span><span class="m">1</span><span class="nb">,.,</span><span class="m">2</span><span class="nb">,</span><span class="m">3</span><span class="nb">,</span><span class="m">4</span><span class="nb">,</span><span class="m">5</span><span class="nb">,</span><span class="m">0</span><span class="nb">,</span><span class="m">0</span><span class="nb">,e,</span><span class="o">+</span><span class="nb">,</span><span class="m">0</span><span class="nb">,</span><span class="m">2</span><span class="o">]</span><span class="nb">}.</span>
</div><div id="l1825" class="code_block">
</div><div id="l1826" class="code_block"><span class="nv">\ourisousageitem</span><span class="nb">{atom</span><span class="nv">\_</span><span class="nb">concat</span><span class="o">(</span><span class="nb">Atom</span><span class="m">1</span><span class="nb">,Atom</span><span class="m">2</span><span class="nb">,Atom</span><span class="m">3</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{atom</span><span class="nv">\_</span><span class="nb">concat</span><span class="o">/</span><span class="m">3</span><span class="nb">}}</span>
</div><div id="l1827" class="code_block"><span class="nv">\ourusage</span><span class="nb">{atom</span><span class="nv">\_</span><span class="nb">concat</span><span class="o">(</span><span class="nb">?Atom,?Atom,</span><span class="o">+</span><span class="nb">Atom</span><span class="o">)</span><span class="nb">}</span>
</div><div id="l1828" class="code_block"><span class="nv">\ourusage</span><span class="nb">{atom</span><span class="nv">\_</span><span class="nb">concat</span><span class="o">(+</span><span class="nb">Atom,</span><span class="o">+</span><span class="nb">Atom,</span><span class="o">-</span><span class="nb">Atom</span><span class="o">)</span><span class="nb">}</span>
</div><div id="l1829" class="code_block">
</div><div id="l1830" class="code_block">
</div><div id="l1831" class="code_block"><span class="nv">\end</span><span class="nb">{description}</span>
</div><div id="l1832" class="code_block">
</div><div id="l1833" class="code_block">
</div><div id="l1834" class="code_block"><span class="nv">\section</span><span class="nb">{All Solutions and Aggregate Predicates}</span>
</div><div id="l1835" class="code_block"><span class="nv">\index</span><span class="nb">{sets, bags} </span><span class="nv">\index</span><span class="nb">{aggregate predicates</span><span class="o">!</span><span class="nb">prolog}</span>
</div><div id="l1836" class="code_block"><span class="c">%-----------------------------------------------------</span>
</div><div id="l1837" class="code_block"><span class="nb">Often there are many solutions to a problem and it is necessary</span>
</div><div id="l1838" class="code_block"><span class="nb">somehow to compare these solutions with one another.  The most general</span>
</div><div id="l1839" class="code_block"><span class="nb">way of doing this is to collect all the solutions into a list, which</span>
</div><div id="l1840" class="code_block"><span class="nb">may then be processed in any way desired.  So XSB provides</span>
</div><div id="l1841" class="code_block"><span class="nb">ISO</span><span class="o">-</span><span class="nb">standard predicates such as {</span><span class="nv">\tt</span><span class="nb"> setof</span><span class="o">/</span><span class="m">3</span><span class="nb">}, {</span><span class="nv">\tt</span><span class="nb"> bagof</span><span class="o">/</span><span class="m">3</span><span class="nb">}, and {</span><span class="nv">\tt</span>
</div><div id="l1842" class="code_block"><span class="nb">findall</span><span class="o">/</span><span class="m">3</span><span class="nb">} to collect solutions into lists.  Sometimes however, one</span>
</div><div id="l1843" class="code_block"><span class="nb">wants simply to perform some aggregate operation over the set of</span>
</div><div id="l1844" class="code_block"><span class="nb">solutions, for example to find the maximum or minimum of the set of</span>
</div><div id="l1845" class="code_block"><span class="nb">solutions.  XSB uses tabling and HiLog to provide a general and</span>
</div><div id="l1846" class="code_block"><span class="nb">powerful aggregation facility as discussed in Section</span>
</div><div id="l1847" class="code_block"><span class="nv">\ref</span><span class="nb">{tabling_aggregate_predicates}.</span>
</div><div id="l1848" class="code_block">
</div><div id="l1849" class="code_block"><span class="nv">\begin</span><span class="nb">{description}</span>
</div><div id="l1850" class="code_block"><span class="nv">\ouritem</span><span class="nb">{setof</span><span class="o">(</span><span class="nb">?X, </span><span class="o">+</span><span class="nb">Goal, ?Set</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{setof</span><span class="o">/</span><span class="m">3</span><span class="nb">}}</span>
</div><div id="l1851" class="code_block"><span class="nb">    This predicate may be read as ``{</span><span class="nv">\tt</span><span class="nb"> Set} is the set of all instances </span>
</div><div id="l1852" class="code_block"><span class="nb">    of {</span><span class="nv">\tt</span><span class="nb"> X} such that {</span><span class="nv">\tt</span><span class="nb"> Goal} is provable&#39;&#39;.</span>
</div><div id="l1853" class="code_block"><span class="nb">    If~{</span><span class="nv">\tt</span><span class="nb"> Goal} is not provable, {</span><span class="nv">\tt</span><span class="nb"> setof</span><span class="o">/</span><span class="m">3</span><span class="nb">} fails.</span>
</div><div id="l1854" class="code_block"><span class="nb">    The term {</span><span class="nv">\tt</span><span class="nb"> Goal} specifies a goal or goals as in {</span><span class="nv">\tt</span><span class="nb"> call</span><span class="o">(</span><span class="nb">Goal</span><span class="o">)</span><span class="nb">}.</span>
</div><div id="l1855" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> Set} is a set of terms represented as a list of those terms,</span>
</div><div id="l1856" class="code_block"><span class="nb">    without duplicates, in the standard order for terms </span>
</div><div id="l1857" class="code_block"><span class="nb">    </span><span class="o">(</span><span class="nb">see Section~</span><span class="nv">\ref</span><span class="nb">{Comparison}</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1858" class="code_block"><span class="nb">    If there are uninstantiated variables in {</span><span class="nv">\tt</span><span class="nb"> Goal} which do not also </span>
</div><div id="l1859" class="code_block"><span class="nb">    appear in {</span><span class="nv">\tt</span><span class="nb"> X}, then a call to this evaluable predicate may backtrack,</span>
</div><div id="l1860" class="code_block"><span class="nb">    generating alternative values for~{</span><span class="nv">\tt</span><span class="nb"> Set} corresponding to different</span>
</div><div id="l1861" class="code_block"><span class="nb">    instantiations of the free variables of~{</span><span class="nv">\tt</span><span class="nb"> Goal}.</span>
</div><div id="l1862" class="code_block"><span class="nb">    Variables occurring in {</span><span class="nv">\tt</span><span class="nb"> Goal} will not be treated as free if they </span>
</div><div id="l1863" class="code_block"><span class="nb">    are explicitly bound within~{</span><span class="nv">\tt</span><span class="nb"> Goal} by an existential quantifier.</span>
</div><div id="l1864" class="code_block"><span class="nb">    An existential quantification can be specified as:</span>
</div><div id="l1865" class="code_block"><span class="nb">    </span><span class="nv">\begin</span><span class="nb">{center}</span>
</div><div id="l1866" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> Y </span><span class="nv">\^\</span><span class="nb"> G}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\^</span><span class="nb">}</span>
</div><div id="l1867" class="code_block"><span class="nb">    </span><span class="nv">\end</span><span class="nb">{center}</span>
</div><div id="l1868" class="code_block"><span class="nb">    meaning there exists a {</span><span class="nv">\tt</span><span class="nb"> Y} such that {</span><span class="nv">\tt</span><span class="nb"> G} is true,</span>
</div><div id="l1869" class="code_block"><span class="nb">    where {</span><span class="nv">\tt</span><span class="nb"> Y} is some Prolog term </span><span class="o">(</span><span class="nb">usually, a variable</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1870" class="code_block"><span class="nb">  </span>
</div><div id="l1871" class="code_block"><span class="nb">    Exceptions: Same as predicate {</span><span class="nv">\tt</span><span class="nb"> call</span><span class="o">/</span><span class="m">1</span><span class="nb">}</span>
</div><div id="l1872" class="code_block"><span class="nb">		</span><span class="o">(</span><span class="nb">see Section~</span><span class="nv">\ref</span><span class="nb">{meta_predicates}</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1873" class="code_block">
</div><div id="l1874" class="code_block"><span class="nv">\ouritem</span><span class="nb">{bagof</span><span class="o">(</span><span class="nb">?X, </span><span class="o">+</span><span class="nb">Goal, ?Bag</span><span class="o">)</span><span class="nb">} </span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{bagof</span><span class="o">/</span><span class="m">3</span><span class="nb">}}</span>
</div><div id="l1875" class="code_block"><span class="nb">    This predicate has the same semantics as {</span><span class="nv">\tt</span><span class="nb"> setof</span><span class="o">/</span><span class="m">3</span><span class="nb">} except that the </span>
</div><div id="l1876" class="code_block"><span class="nb">    third argument returns an unordered list that may contain duplicates.</span>
</div><div id="l1877" class="code_block">
</div><div id="l1878" class="code_block"><span class="nb">    Exceptions: Same as predicate {</span><span class="nv">\tt</span><span class="nb"> call</span><span class="o">/</span><span class="m">1</span><span class="nb">}</span>
</div><div id="l1879" class="code_block"><span class="nb">		</span><span class="o">(</span><span class="nb">see Section~</span><span class="nv">\ref</span><span class="nb">{meta_predicates}</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1880" class="code_block">
</div><div id="l1881" class="code_block"><span class="nv">\ouritem</span><span class="nb">{findall</span><span class="o">(</span><span class="nb">?X, </span><span class="o">+</span><span class="nb">Goal, ?List</span><span class="o">)</span><span class="nb">} </span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{findall</span><span class="o">/</span><span class="m">3</span><span class="nb">}}</span>
</div><div id="l1882" class="code_block"><span class="nb">    Similar to predicate {</span><span class="nv">\tt</span><span class="nb"> bagof</span><span class="o">/</span><span class="m">3</span><span class="nb">}, except that variables in {</span><span class="nv">\tt</span><span class="nb"> Goal}</span>
</div><div id="l1883" class="code_block"><span class="nb">    that do not occur in {</span><span class="nv">\tt</span><span class="nb"> X} are treated as existential, and alternative</span>
</div><div id="l1884" class="code_block"><span class="nb">    lists are not returned for different bindings of such variables.  This</span>
</div><div id="l1885" class="code_block"><span class="nb">    makes {</span><span class="nv">\tt</span><span class="nb"> findall</span><span class="o">/</span><span class="m">3</span><span class="nb">} deterministic </span><span class="o">(</span><span class="nb">non</span><span class="o">-</span><span class="nb">backtrackable</span><span class="o">)</span><span class="nb">.  Unlike</span>
</div><div id="l1886" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> setof</span><span class="o">/</span><span class="m">3</span><span class="nb">} and {</span><span class="nv">\tt</span><span class="nb"> bagof</span><span class="o">/</span><span class="m">3</span><span class="nb">}, if {</span><span class="nv">\tt</span><span class="nb"> Goal} is unsatisfiable,</span>
</div><div id="l1887" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> findall</span><span class="o">/</span><span class="m">3</span><span class="nb">} succeeds binding {</span><span class="nv">\tt</span><span class="nb"> List} to the empty list.</span>
</div><div id="l1888" class="code_block">
</div><div id="l1889" class="code_block"><span class="nb">    Exceptions: Same as predicate {</span><span class="nv">\tt</span><span class="nb"> call</span><span class="o">/</span><span class="m">1</span><span class="nb">}</span>
</div><div id="l1890" class="code_block"><span class="nb">		</span><span class="o">(</span><span class="nb">see Section~</span><span class="nv">\ref</span><span class="nb">{meta_predicates}</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1891" class="code_block">
</div><div id="l1892" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{tfindall</span><span class="o">(</span><span class="nb">?X, </span><span class="o">+</span><span class="nb">Goal, ?List</span><span class="o">)</span><span class="nb">}{Tabling}</span>
</div><div id="l1893" class="code_block"><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{tfindall</span><span class="o">/</span><span class="m">3</span><span class="nb">}}</span>
</div><div id="l1894" class="code_block"><span class="c">%\predindex{tfindall/3~(L)}</span>
</div><div id="l1895" class="code_block"><span class="nv">\label</span><span class="nb">{tfindall</span><span class="o">/</span><span class="m">3</span><span class="nb">}</span>
</div><div id="l1896" class="code_block">
</div><div id="l1897" class="code_block"><span class="nb">    {</span><span class="nv">\em</span><span class="nb"> Note: {</span><span class="nv">\tt</span><span class="nb"> tfindall</span><span class="o">/</span><span class="m">3</span><span class="nb">} may be deprecated in current versions.</span>
</div><div id="l1898" class="code_block"><span class="nb">    Please use the predicates described in</span>
</div><div id="l1899" class="code_block"><span class="nb">    Section~</span><span class="nv">\ref</span><span class="nb">{tabling_aggregate_predicates} if possible}.</span>
</div><div id="l1900" class="code_block">
</div><div id="l1901" class="code_block"><span class="nb">    Like {</span><span class="nv">\tt</span><span class="nb"> findall</span><span class="o">/</span><span class="m">3</span><span class="nb">}, {</span><span class="nv">\tt</span><span class="nb"> tfindall</span><span class="o">/</span><span class="m">3</span><span class="nb">} treats all variables in</span>
</div><div id="l1902" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> Goal} that do not occur in {</span><span class="nv">\tt</span><span class="nb"> X} as existential.  However,</span>
</div><div id="l1903" class="code_block"><span class="nb">    in {</span><span class="nv">\tt</span><span class="nb"> tfindall</span><span class="o">/</span><span class="m">3</span><span class="nb">}, the {</span><span class="nv">\tt</span><span class="nb"> Goal} must be a call to a single</span>
</div><div id="l1904" class="code_block"><span class="nb">    tabled predicate.</span>
</div><div id="l1905" class="code_block"><span class="nb">	</span>
</div><div id="l1906" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> tfindall</span><span class="o">/</span><span class="m">3</span><span class="nb">} allows the user to build programs that use</span>
</div><div id="l1907" class="code_block"><span class="nb">    stratified aggregation.  If the table to {</span><span class="nv">\tt</span><span class="nb"> Goal} is incomplete,</span>
</div><div id="l1908" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> tfindall</span><span class="o">/</span><span class="m">3</span><span class="nb">} suspends until the table has been completed, and</span>
</div><div id="l1909" class="code_block"><span class="nb">    only then computes {</span><span class="nv">\tt</span><span class="nb"> List}.  See Chapter~</span><span class="nv">\ref</span><span class="nb">{chap:TablingOverview}</span>
</div><div id="l1910" class="code_block"><span class="nb">    for further discussion of {</span><span class="nv">\tt</span><span class="nb"> tfindall</span><span class="o">/</span><span class="m">3</span><span class="nb">}.  Like {</span><span class="nv">\tt</span><span class="nb"> findall</span><span class="o">/</span><span class="m">3</span><span class="nb">},</span>
</div><div id="l1911" class="code_block"><span class="nb">    if {</span><span class="nv">\tt</span><span class="nb"> Goal} is unsatisfiable, {</span><span class="nv">\tt</span><span class="nb"> tfindall</span><span class="o">/</span><span class="m">3</span><span class="nb">} succeeds binding</span>
</div><div id="l1912" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> List} to the empty list.</span>
</div><div id="l1913" class="code_block">
</div><div id="l1914" class="code_block"><span class="nb">    Some of the differences between predicates {</span><span class="nv">\tt</span><span class="nb"> findall</span><span class="o">/</span><span class="m">3</span><span class="nb">} and</span>
</div><div id="l1915" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> tfindall</span><span class="o">/</span><span class="m">3</span><span class="nb">} can be seen from the following example:</span>
</div><div id="l1916" class="code_block">
</div><div id="l1917" class="code_block"><span class="nb">    {</span><span class="nv">\footnotesize</span>
</div><div id="l1918" class="code_block"><span class="nb">    </span><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l1919" class="code_block"><span class="nb">            | ?</span><span class="o">-</span><span class="nb"> </span><span class="o">[</span><span class="nb">user</span><span class="o">]</span><span class="nb">.</span>
</div><div id="l1920" class="code_block"><span class="nb">            </span><span class="o">[</span><span class="nb">Compiling user</span><span class="o">]</span>
</div><div id="l1921" class="code_block"><span class="nb">            :</span><span class="o">-</span><span class="nb"> table p</span><span class="o">/</span><span class="m">1</span><span class="nb">.</span>
</div><div id="l1922" class="code_block"><span class="nb">            p</span><span class="o">(</span><span class="nb">a</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1923" class="code_block"><span class="nb">            p</span><span class="o">(</span><span class="nb">b</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1924" class="code_block"><span class="nb">            </span><span class="o">[</span><span class="nb">user compiled, cpu time used: </span><span class="m">0</span><span class="nb">.</span><span class="m">639</span><span class="nb"> seconds</span><span class="o">]</span>
</div><div id="l1925" class="code_block"><span class="nb">            </span><span class="o">[</span><span class="nb">user loaded</span><span class="o">]</span>
</div><div id="l1926" class="code_block">
</div><div id="l1927" class="code_block"><span class="nb">            yes</span>
</div><div id="l1928" class="code_block"><span class="nb">            | ?</span><span class="o">-</span><span class="nb"> p</span><span class="o">(</span><span class="nb">X</span><span class="o">)</span><span class="nb">, findall</span><span class="o">(</span><span class="nb">Y, p</span><span class="o">(</span><span class="nb">Y</span><span class="o">)</span><span class="nb">, L</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1929" class="code_block">
</div><div id="l1930" class="code_block"><span class="nb">            X </span><span class="o">=</span><span class="nb"> a</span>
</div><div id="l1931" class="code_block"><span class="nb">            Y </span><span class="o">=</span><span class="nb"> _</span><span class="m">922928</span>
</div><div id="l1932" class="code_block"><span class="nb">            L </span><span class="o">=</span><span class="nb"> </span><span class="o">[</span><span class="nb">a</span><span class="o">]</span><span class="nb">;</span>
</div><div id="l1933" class="code_block">
</div><div id="l1934" class="code_block"><span class="nb">            X </span><span class="o">=</span><span class="nb"> b</span>
</div><div id="l1935" class="code_block"><span class="nb">            Y </span><span class="o">=</span><span class="nb"> _</span><span class="m">922820</span>
</div><div id="l1936" class="code_block"><span class="nb">            L </span><span class="o">=</span><span class="nb"> </span><span class="o">[</span><span class="nb">a,b</span><span class="o">]</span><span class="nb">;</span>
</div><div id="l1937" class="code_block">
</div><div id="l1938" class="code_block"><span class="nb">            no</span>
</div><div id="l1939" class="code_block"><span class="nb">            | ?</span><span class="o">-</span><span class="nb"> abolish_all_tables.</span>
</div><div id="l1940" class="code_block">
</div><div id="l1941" class="code_block"><span class="nb">            yes</span>
</div><div id="l1942" class="code_block"><span class="nb">            | ?</span><span class="o">-</span><span class="nb"> p</span><span class="o">(</span><span class="nb">X</span><span class="o">)</span><span class="nb">, tfindall</span><span class="o">(</span><span class="nb">Y, p</span><span class="o">(</span><span class="nb">Y</span><span class="o">)</span><span class="nb">, L</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1943" class="code_block">
</div><div id="l1944" class="code_block"><span class="nb">            X </span><span class="o">=</span><span class="nb"> b</span>
</div><div id="l1945" class="code_block"><span class="nb">            Y </span><span class="o">=</span><span class="nb"> _</span><span class="m">922820</span>
</div><div id="l1946" class="code_block"><span class="nb">            L </span><span class="o">=</span><span class="nb"> </span><span class="o">[</span><span class="nb">b,a</span><span class="o">]</span><span class="nb">;</span>
</div><div id="l1947" class="code_block">
</div><div id="l1948" class="code_block"><span class="nb">            X </span><span class="o">=</span><span class="nb"> a</span>
</div><div id="l1949" class="code_block"><span class="nb">            Y </span><span class="o">=</span><span class="nb"> _</span><span class="m">922820</span>
</div><div id="l1950" class="code_block"><span class="nb">            L </span><span class="o">=</span><span class="nb"> </span><span class="o">[</span><span class="nb">b,a</span><span class="o">]</span><span class="nb">;</span>
</div><div id="l1951" class="code_block">
</div><div id="l1952" class="code_block"><span class="nb">            no</span>
</div><div id="l1953" class="code_block"><span class="nb">    </span><span class="nv">\end</span><span class="nb">{verbatim}</span>
</div><div id="l1954" class="code_block"><span class="nb">    }</span>
</div><div id="l1955" class="code_block">
</div><div id="l1956" class="code_block"><span class="nb">    Exceptions: Same as predicate {</span><span class="nv">\tt</span><span class="nb"> findall</span><span class="o">/</span><span class="m">3</span><span class="nb">} </span><span class="o">(</span><span class="nb">see above</span><span class="o">)</span><span class="nb">.  Also:</span>
</div><div id="l1957" class="code_block"><span class="nb">    </span><span class="nv">\begin</span><span class="nb">{description}</span>
</div><div id="l1958" class="code_block"><span class="nb">    </span><span class="nv">\item</span><span class="o">[</span><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> table</span><span class="nv">\_</span><span class="nb">error}</span><span class="o">]</span>
</div><div id="l1959" class="code_block"><span class="nb">	Upon execution {</span><span class="nv">\tt</span><span class="nb"> Goal} is not a subgoal of a tabled predicate.</span>
</div><div id="l1960" class="code_block"><span class="nb">    </span><span class="nv">\end</span><span class="nb">{description}</span>
</div><div id="l1961" class="code_block">
</div><div id="l1962" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{tbagof</span><span class="o">(</span><span class="nb">?X, </span><span class="o">+</span><span class="nb">Goal, ?List</span><span class="o">)</span><span class="nb"> </span><span class="o">/</span><span class="nb"> tsetof</span><span class="o">(</span><span class="nb">?X, </span><span class="o">+</span><span class="nb">Goal, ?List</span><span class="o">)</span><span class="nb">}{Tabling}</span>
</div><div id="l1963" class="code_block"><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{tsetof</span><span class="o">/</span><span class="m">3</span><span class="nb">}}</span>
</div><div id="l1964" class="code_block"><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{tbagof</span><span class="o">/</span><span class="m">3</span><span class="nb">}}</span>
</div><div id="l1965" class="code_block">
</div><div id="l1966" class="code_block"><span class="nb">    {</span><span class="nv">\em</span><span class="nb"> Note: {</span><span class="nv">\tt</span><span class="nb"> tbagof</span><span class="o">/</span><span class="m">3</span><span class="nb">} and {</span><span class="nv">\tt</span><span class="nb"> tsetof</span><span class="o">/</span><span class="m">3</span><span class="nb">} may be deprecated in</span>
</div><div id="l1967" class="code_block"><span class="nb">    current versions.  Please use the predicates described in</span>
</div><div id="l1968" class="code_block"><span class="nb">    Section~</span><span class="nv">\ref</span><span class="nb">{tabling_aggregate_predicates} if possible.}</span>
</div><div id="l1969" class="code_block">
</div><div id="l1970" class="code_block"><span class="nb">The standard predicates {</span><span class="nv">\tt</span><span class="nb"> tbagof</span><span class="o">/</span><span class="m">3</span><span class="nb">} and {</span><span class="nv">\tt</span><span class="nb"> tsetof</span><span class="o">/</span><span class="m">3</span><span class="nb">} provide</span>
</div><div id="l1971" class="code_block"><span class="nb">tabled versions of {</span><span class="nv">\tt</span><span class="nb"> bagof</span><span class="o">/</span><span class="m">3</span><span class="nb">} and {</span><span class="nv">\tt</span><span class="nb"> setof</span><span class="o">/</span><span class="m">3</span><span class="nb">} in a similar manner</span>
</div><div id="l1972" class="code_block"><span class="nb">to the way in which {</span><span class="nv">\tt</span><span class="nb"> tfindall</span><span class="o">/</span><span class="m">3</span><span class="nb">} provides a tabled version of {</span><span class="nv">\tt</span>
</div><div id="l1973" class="code_block"><span class="nb">findall</span><span class="o">/</span><span class="m">3</span><span class="nb">}.</span>
</div><div id="l1974" class="code_block">
</div><div id="l1975" class="code_block"><span class="nv">\ouritem</span><span class="nb">{X </span><span class="nv">\^\</span><span class="nb"> Goal}</span>
</div><div id="l1976" class="code_block"><span class="c">%\predindex{$\wedge/2$~(L)}\index{$\wedge/2$|bold}</span>
</div><div id="l1977" class="code_block"><span class="nb">    The system recognises this as meaning there exists an {</span><span class="nv">\tt</span><span class="nb"> X} such</span>
</div><div id="l1978" class="code_block"><span class="nb">    that {</span><span class="nv">\tt</span><span class="nb"> Goal} is true, and treats it as equivalent to {</span><span class="nv">\tt</span><span class="nb"> call</span><span class="o">(</span><span class="nb">Goal</span><span class="o">)</span><span class="nb">}.</span>
</div><div id="l1979" class="code_block"><span class="nb">    The use of this explicit existential quantifier outside predicates</span>
</div><div id="l1980" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> setof</span><span class="o">/</span><span class="m">3</span><span class="nb">} and {</span><span class="nv">\tt</span><span class="nb"> bagof</span><span class="o">/</span><span class="m">3</span><span class="nb">} constructs is superfluous.</span>
</div><div id="l1981" class="code_block"><span class="nv">\end</span><span class="nb">{description}</span>
</div><div id="l1982" class="code_block">
</div><div id="l1983" class="code_block"><span class="nv">\subsection</span><span class="nb">{Tabling Aggregate Predicates}</span><span class="nv">\label</span><span class="nb">{tabling_aggregate_predicates}</span>
</div><div id="l1984" class="code_block"><span class="c">%-------------------------------------------------------------------------</span>
</div><div id="l1985" class="code_block"><span class="nv">\index</span><span class="nb">{aggregate predicates</span><span class="o">!</span><span class="nb">tabling} </span><span class="nv">\index</span><span class="nb">{tabling</span><span class="o">!</span><span class="nb">aggregate predicates}</span>
</div><div id="l1986" class="code_block"><span class="c">%-------------------------------------------------------------------------</span>
</div><div id="l1987" class="code_block">
</div><div id="l1988" class="code_block"><span class="nb">HiLog provides an elegant way to introduce aggregate operations into</span>
</div><div id="l1989" class="code_block"><span class="nb">XSB.  HiLog allows a user to define named </span><span class="o">(</span><span class="nb">and parameterized</span><span class="o">)</span><span class="nb"> sets </span><span class="o">(</span><span class="nb">or</span>
</div><div id="l1990" class="code_block"><span class="nb">bags</span><span class="o">)</span><span class="nb">.  For example, say we have a simple database</span><span class="o">-</span><span class="nb">like predicate,</span>
</div><div id="l1991" class="code_block"><span class="nv">\verb</span><span class="nb">|employee</span><span class="o">(</span><span class="nb">Name,Dept,Sal</span><span class="o">)</span><span class="nb">|, which contains a tuple for each</span>
</div><div id="l1992" class="code_block"><span class="nb">employee in our concern and contains the employee&#39;s name, department,</span>
</div><div id="l1993" class="code_block"><span class="nb">and salary.  From this predicate we can construct a set, or bag</span>
</div><div id="l1994" class="code_block"><span class="nb">really, that contains all the salaries of employees in the relation:</span>
</div><div id="l1995" class="code_block"><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l1996" class="code_block"><span class="nb">    :</span><span class="o">-</span><span class="nb"> hilog salaries.</span>
</div><div id="l1997" class="code_block"><span class="nb">    salaries</span><span class="o">(</span><span class="nb">Sal</span><span class="o">)</span><span class="nb"> :</span><span class="o">-</span><span class="nb"> employee</span><span class="o">(</span><span class="nb">_Name,_Dept,Sal</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l1998" class="code_block"><span class="nv">\end</span><span class="nb">{verbatim}</span>
</div><div id="l1999" class="code_block"><span class="nb">So </span><span class="nv">\verb</span><span class="nb">|salaries| is the name of a unary predicate that is true of</span>
</div><div id="l2000" class="code_block"><span class="nb">all salaries, or rather is the name of a {</span><span class="nv">\em</span><span class="nb"> bag} of all salaries.</span>
</div><div id="l2001" class="code_block"><span class="nb">It is a bag since it may contain the same salary multiple times.</span>
</div><div id="l2002" class="code_block"><span class="nb">XSB provides a predicate </span><span class="nv">\verb</span><span class="nb">|bagSum| which can be used to</span>
</div><div id="l2003" class="code_block"><span class="nb">sum up the elements in a named bag.  So given the definition of the</span>
</div><div id="l2004" class="code_block"><span class="nb">HiLog predicate </span><span class="nv">\verb</span><span class="nb">|salaries</span><span class="o">/</span><span class="m">1</span><span class="nb">| above, we can get the sum of all the</span>
</div><div id="l2005" class="code_block"><span class="nb">salaries with:</span>
</div><div id="l2006" class="code_block"><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l2007" class="code_block"><span class="nb">    :</span><span class="o">-</span><span class="nb"> bagSum</span><span class="o">(</span><span class="nb">salaries,TotalSals</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l2008" class="code_block"><span class="nv">\end</span><span class="nb">{verbatim}</span>
</div><div id="l2009" class="code_block"><span class="nb">The first argument to </span><span class="nv">\verb</span><span class="nb">|bagSum| is the name of a bag, and the</span>
</div><div id="l2010" class="code_block"><span class="nb">second is bound to the sum of the elements in the bag.</span>
</div><div id="l2011" class="code_block">
</div><div id="l2012" class="code_block"><span class="nb">We can also do a ``group by&#39;&#39; to get total salaries within departments</span>
</div><div id="l2013" class="code_block"><span class="nb">as follows.  We define a parameterized predicate, </span><span class="nv">\verb</span><span class="nb">|sals</span><span class="o">(</span><span class="nb">Dept</span><span class="o">)</span><span class="nb">|,</span>
</div><div id="l2014" class="code_block"><span class="nb">to be the bag of salaries of employees in department </span><span class="nv">\verb</span><span class="nb">|Dept|, as</span>
</div><div id="l2015" class="code_block"><span class="nb">follows:</span>
</div><div id="l2016" class="code_block"><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l2017" class="code_block"><span class="nb">    sals</span><span class="o">(</span><span class="nb">Dept</span><span class="o">)(</span><span class="nb">Sal</span><span class="o">)</span><span class="nb"> :</span><span class="o">-</span><span class="nb"> employee</span><span class="o">(</span><span class="nb">_Name,Dept,Sal</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l2018" class="code_block"><span class="nv">\end</span><span class="nb">{verbatim}</span>
</div><div id="l2019" class="code_block"><span class="nb">This rule says that </span><span class="nv">\verb</span><span class="nb">|Sal| is in the bag named </span><span class="nv">\verb</span><span class="nb">|sals</span><span class="o">(</span><span class="nb">Dept</span><span class="o">)</span><span class="nb">|</span>
</div><div id="l2020" class="code_block"><span class="nb">if there is an employee with some name who works in department</span>
</div><div id="l2021" class="code_block"><span class="nv">\verb</span><span class="nb">|Dept| and has salary </span><span class="nv">\verb</span><span class="nb">|Sal|.</span>
</div><div id="l2022" class="code_block">
</div><div id="l2023" class="code_block"><span class="nb">Now with this definition, we can define a predicate,</span>
</div><div id="l2024" class="code_block"><span class="nv">\verb</span><span class="nb">|deptPayroll</span><span class="o">/</span><span class="m">2</span><span class="nb">|, that associates with each department the sum of</span>
</div><div id="l2025" class="code_block"><span class="nb">all the salaries of employees in that department:</span>
</div><div id="l2026" class="code_block"><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l2027" class="code_block"><span class="nb">    deptPayroll</span><span class="o">(</span><span class="nb">Dept,Payroll</span><span class="o">)</span><span class="nb"> :</span><span class="o">-</span><span class="nb"> bagSum</span><span class="o">(</span><span class="nb">sals</span><span class="o">(</span><span class="nb">Dept</span><span class="o">)</span><span class="nb">,Payroll</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l2028" class="code_block"><span class="nv">\end</span><span class="nb">{verbatim}</span>
</div><div id="l2029" class="code_block">
</div><div id="l2030" class="code_block"><span class="nb">XSB provides analogous aggregate operators, described below, to</span>
</div><div id="l2031" class="code_block"><span class="nb">compute the minimum, maximum, count, and average, of a bag,</span>
</div><div id="l2032" class="code_block"><span class="nb">respectively.  These predicates are all defined using a more basic</span>
</div><div id="l2033" class="code_block"><span class="nb">predicate </span><span class="nv">\verb</span><span class="nb">|bagReduce</span><span class="o">/</span><span class="m">4</span><span class="nb">|.</span>
</div><div id="l2034" class="code_block">
</div><div id="l2035" class="code_block"><span class="nv">\begin</span><span class="nb">{description}</span>
</div><div id="l2036" class="code_block">
</div><div id="l2037" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{bagReduce</span><span class="o">(</span><span class="nb">?SetPred,?Arg,</span><span class="o">+</span><span class="nb">Op,</span><span class="o">+</span><span class="nb">Id</span><span class="o">)</span><span class="nb">}{HiLog,Tabling}</span>
</div><div id="l2038" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{filterReduce</span><span class="o">(</span><span class="nb">?SetPred,?Arg,</span><span class="o">+</span><span class="nb">Op,</span><span class="o">+</span><span class="nb">Id</span><span class="o">)</span><span class="nb">}{Tabling}</span>
</div><div id="l2039" class="code_block"><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{bagReduce</span><span class="o">/</span><span class="m">4</span><span class="nb">}} </span>
</div><div id="l2040" class="code_block"><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{filterReduce</span><span class="o">/</span><span class="m">4</span><span class="nb">}} </span>
</div><div id="l2041" class="code_block"><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> SetPred} must be a HiLog set specification, i.e., a unary HiLog</span>
</div><div id="l2042" class="code_block"><span class="nb">predicate.  {</span><span class="nv">\tt</span><span class="nb"> Op} must be a Hilog operation, i.e., a </span><span class="m">3</span><span class="o">-</span><span class="nb">ary HiLog</span>
</div><div id="l2043" class="code_block"><span class="nb">predicate that defines an associative operator.  The predicate must</span>
</div><div id="l2044" class="code_block"><span class="nb">define a binary function in which the first two arguments determine</span>
</div><div id="l2045" class="code_block"><span class="nb">the third.  {</span><span class="nv">\tt</span><span class="nb"> Id} must be the identity of the operator.  {</span><span class="nv">\tt</span>
</div><div id="l2046" class="code_block"><span class="nb">bagReduce} returns with {</span><span class="nv">\tt</span><span class="nb"> Arg} bound to the ``reduce&#39;&#39; of the</span>
</div><div id="l2047" class="code_block"><span class="nb">elements of the bag determined by {</span><span class="nv">\tt</span><span class="nb"> SetPred} under the operation</span>
</div><div id="l2048" class="code_block"><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> Op}.  I.e., {</span><span class="nv">\tt</span><span class="nb"> Arg} becomes the result of applying the operator</span>
</div><div id="l2049" class="code_block"><span class="nb">to all the elements in the bag that unify with {</span><span class="nv">\tt</span><span class="nb"> SetPred}.  See the</span>
</div><div id="l2050" class="code_block"><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> bagSum} operator below to see an example of {</span><span class="nv">\tt</span><span class="nb"> bagReduce}&#39;s</span>
</div><div id="l2051" class="code_block"><span class="nb">use.</span>
</div><div id="l2052" class="code_block">
</div><div id="l2053" class="code_block"><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> filterReduce</span><span class="o">/</span><span class="m">4</span><span class="nb">} acts as {</span><span class="nv">\tt</span><span class="nb"> bagReduce</span><span class="o">/</span><span class="m">4</span><span class="nb">} with two differences.</span>
</div><div id="l2054" class="code_block"><span class="nb">First, it does not depend on HiLog, so that {</span><span class="nv">\tt</span><span class="nb"> filterReduce</span><span class="o">/</span><span class="m">4</span><span class="nb">} will</span>
</div><div id="l2055" class="code_block"><span class="nb">be more robust especially when XSB&#39;s module system is used.  In</span>
</div><div id="l2056" class="code_block"><span class="nb">addition, {</span><span class="nv">\tt</span><span class="nb"> filterReduce</span><span class="o">/</span><span class="m">4</span><span class="nb">} aggregates solutions to {</span><span class="nv">\tt</span><span class="nb"> Pred}</span>
</div><div id="l2057" class="code_block"><span class="nb">using a variance rather than unification.  An example of the use of</span>
</div><div id="l2058" class="code_block"><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> filterReduce</span><span class="o">/</span><span class="m">4</span><span class="nb">} is given in Chapter </span><span class="nv">\ref</span><span class="nb">{chap:TablingOverview}.</span>
</div><div id="l2059" class="code_block">
</div><div id="l2060" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{bagPO</span><span class="o">(</span><span class="nb">?SetPred,?Arg,</span><span class="o">+</span><span class="nb">Order</span><span class="o">)</span><span class="nb">}{HiLog,Tabling}</span>
</div><div id="l2061" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{filterPO</span><span class="o">(</span><span class="nb">?SetPred,?Arg,</span><span class="o">+</span><span class="nb">Order</span><span class="o">)</span><span class="nb">}{Tabling}</span>
</div><div id="l2062" class="code_block"><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{bagPO</span><span class="o">/</span><span class="m">3</span><span class="nb">}}</span>
</div><div id="l2063" class="code_block"><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{filterPO</span><span class="o">/</span><span class="m">3</span><span class="nb">}}</span>
</div><div id="l2064" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> SetPred} must be a HiLog set specification, i.e., a unary</span>
</div><div id="l2065" class="code_block"><span class="nb">    HiLog predicate.  {</span><span class="nv">\tt</span><span class="nb"> Order} must be a binary Hilog relation that</span>
</div><div id="l2066" class="code_block"><span class="nb">    defines a partial order.  {</span><span class="nv">\tt</span><span class="nb"> bagPO} returns nondeterministically</span>
</div><div id="l2067" class="code_block"><span class="nb">    with {</span><span class="nv">\tt</span><span class="nb"> Arg} bound to the maximal elements, under {</span><span class="nv">\tt</span><span class="nb"> Order}, of</span>
</div><div id="l2068" class="code_block"><span class="nb">    the bag {</span><span class="nv">\tt</span><span class="nb"> SetPred}.  {</span><span class="nv">\tt</span><span class="nb"> bagPO</span><span class="o">/</span><span class="m">3</span><span class="nb">} can be used with {</span><span class="nv">\tt</span><span class="nb"> Order}</span>
</div><div id="l2069" class="code_block"><span class="nb">    being subsumption to reduce a set of answers and keep only the most</span>
</div><div id="l2070" class="code_block"><span class="nb">    general answers.</span>
</div><div id="l2071" class="code_block">
</div><div id="l2072" class="code_block"><span class="nb">    See the {</span><span class="nv">\tt</span><span class="nb"> bagMax} operator below to see an example of {</span><span class="nv">\tt</span>
</div><div id="l2073" class="code_block"><span class="nb">    bagPO}&#39;s use.</span>
</div><div id="l2074" class="code_block">
</div><div id="l2075" class="code_block"><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> filterPO</span><span class="o">/</span><span class="m">3</span><span class="nb">} acts as {</span><span class="nv">\tt</span><span class="nb"> bagPO</span><span class="o">/</span><span class="m">3</span><span class="nb">} with the single difference that</span>
</div><div id="l2076" class="code_block"><span class="nb">it does not depend on HiLog, so that {</span><span class="nv">\tt</span><span class="nb"> filterPO</span><span class="o">/</span><span class="m">3</span><span class="nb">} will be more</span>
</div><div id="l2077" class="code_block"><span class="nb">robust especially when XSB&#39;s module system is used.</span>
</div><div id="l2078" class="code_block">
</div><div id="l2079" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{filterPO</span><span class="o">(</span><span class="nv">\#</span><span class="nb">Pred,</span><span class="o">+</span><span class="nb">Order</span><span class="o">)</span><span class="nb">}{Tabling} </span>
</div><div id="l2080" class="code_block"><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{filterPO</span><span class="o">/</span><span class="m">2</span><span class="nb">}} </span>
</div><div id="l2081" class="code_block">
</div><div id="l2082" class="code_block"><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> filterPO</span><span class="o">(</span><span class="nv">\#</span><span class="nb">Pred,</span><span class="o">+</span><span class="nb">Order</span><span class="o">)</span><span class="nb">} succeds only for a solution </span><span class="s">$</span>Pred<span class="k">\theta</span><span class="s">$</span>
</div><div id="l2083" class="code_block"><span class="nb">of {</span><span class="nv">\tt</span><span class="nb"> Pred} for which there is no solution </span><span class="s">$</span>Pred<span class="k">\eta</span><span class="s">$</span><span class="nb"> to {</span><span class="nv">\tt</span><span class="nb"> Pred}</span>
</div><div id="l2084" class="code_block"><span class="nb">such that {</span><span class="nv">\tt</span><span class="nb"> Order</span><span class="o">(</span><span class="s">$</span>Pred<span class="k">\eta</span><span class="s">$</span><span class="nb">,</span><span class="s">$</span>Pred<span class="k">\theta</span><span class="s">$</span><span class="o">)</span><span class="nb">}.</span>
</div><div id="l2085" class="code_block">
</div><div id="l2086" class="code_block"><span class="nb">Example:</span>
</div><div id="l2087" class="code_block">
</div><div id="l2088" class="code_block"><span class="nb">For the following program</span>
</div><div id="l2089" class="code_block"><span class="nb">     </span><span class="nv">\begin</span><span class="nb">{center}</span>
</div><div id="l2090" class="code_block"><span class="nb">     {</span><span class="nv">\tt</span>
</div><div id="l2091" class="code_block"><span class="nb">     </span><span class="nv">\begin</span><span class="nb">{tabular}{l}</span>
</div><div id="l2092" class="code_block"><span class="nb">          :</span><span class="o">-</span><span class="nb"> table p</span><span class="o">/</span><span class="m">2</span><span class="nb">.	</span><span class="nv">\\</span>
</div><div id="l2093" class="code_block"><span class="nb">          b</span><span class="o">(</span><span class="m">1</span><span class="nb">,</span><span class="m">2</span><span class="o">)</span><span class="nb">.       </span><span class="nv">\\</span>
</div><div id="l2094" class="code_block"><span class="nb">          p</span><span class="o">(</span><span class="m">1</span><span class="nb">,</span><span class="m">3</span><span class="o">)</span><span class="nb">.       </span><span class="nv">\\</span>
</div><div id="l2095" class="code_block"><span class="nb">          b</span><span class="o">(</span><span class="m">1</span><span class="nb">,</span><span class="m">1</span><span class="o">)</span><span class="nb">.       </span><span class="nv">\\</span>
</div><div id="l2096" class="code_block"><span class="nv">\\</span>
</div><div id="l2097" class="code_block"><span class="nb">	  prefer</span><span class="o">(</span><span class="nb">b</span><span class="o">(</span><span class="nb">X,X</span><span class="o">)</span><span class="nb">,b</span><span class="o">(</span><span class="nb">X,Y</span><span class="o">))</span><span class="nb">:</span><span class="o">-</span><span class="nb"> X </span><span class="nv">\=</span><span class="o">=</span><span class="nb"> Y. </span>
</div><div id="l2098" class="code_block"><span class="nb">     </span><span class="nv">\end</span><span class="nb">{tabular}</span>
</div><div id="l2099" class="code_block"><span class="nb">     }</span>
</div><div id="l2100" class="code_block"><span class="nb">     </span><span class="nv">\end</span><span class="nb">{center}</span>
</div><div id="l2101" class="code_block"><span class="nb">the query </span>
</div><div id="l2102" class="code_block"><span class="nv">\begin</span><span class="nb">{center}</span>
</div><div id="l2103" class="code_block"><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> ?</span><span class="o">-</span><span class="nb"> filterPO</span><span class="o">(</span><span class="nb">b</span><span class="o">(</span><span class="nb">X,Y</span><span class="o">)</span><span class="nb">}</span>
</div><div id="l2104" class="code_block"><span class="nv">\end</span><span class="nb">{center}</span>
</div><div id="l2105" class="code_block"><span class="nb">will succeed only with the binding {</span><span class="nv">\em</span><span class="nb"> X </span><span class="o">=</span><span class="nb"> </span><span class="m">1</span><span class="nb">,Y </span><span class="o">=</span><span class="nb"> </span><span class="m">1</span><span class="nb">}.</span>
</div><div id="l2106" class="code_block">
</div><div id="l2107" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{bagMax</span><span class="o">(</span><span class="nb">?SetPred,?Arg</span><span class="o">)</span><span class="nb">}{HiLog,Tabling}</span>
</div><div id="l2108" class="code_block"><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{bagMax</span><span class="o">/</span><span class="m">2</span><span class="nb">}}</span>
</div><div id="l2109" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> SetPred} must be a HiLog set specification, i.e., a unary</span>
</div><div id="l2110" class="code_block"><span class="nb">    HiLog predicate.  {</span><span class="nv">\tt</span><span class="nb"> bagMax} returns with {</span><span class="nv">\tt</span><span class="nb"> Arg} bound to the</span>
</div><div id="l2111" class="code_block"><span class="nb">    maximum element </span><span class="o">(</span><span class="nb">under the Prolog term ordering</span><span class="o">)</span><span class="nb"> of the set {</span><span class="nv">\tt</span>
</div><div id="l2112" class="code_block"><span class="nb">    SetPred}.  To use this predicate, it must be imported from aggregs,</span>
</div><div id="l2113" class="code_block"><span class="nb">    and you must give the following definitions in the main module {</span><span class="nv">\tt</span>
</div><div id="l2114" class="code_block"><span class="nb">    usermod}:</span>
</div><div id="l2115" class="code_block"><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l2116" class="code_block"><span class="nb">:</span><span class="o">-</span><span class="nb"> hilog maximum.</span>
</div><div id="l2117" class="code_block"><span class="nb">maximum</span><span class="o">(</span><span class="nb">X,Y,Z</span><span class="o">)</span><span class="nb"> :</span><span class="o">-</span><span class="nb"> X @&lt; Y </span><span class="o">-</span><span class="nb">&gt; Z</span><span class="o">=</span><span class="nb">Y ; Z</span><span class="o">=</span><span class="nb">X.</span>
</div><div id="l2118" class="code_block"><span class="nv">\end</span><span class="nb">{verbatim}</span>
</div><div id="l2119" class="code_block"><span class="nb">    </span><span class="o">(</span><span class="nb">These decarations are necessary because of a current limitation in</span>
</div><div id="l2120" class="code_block"><span class="nb">    how HiLog predicates can be used.  This requirement will be lifted in</span>
</div><div id="l2121" class="code_block"><span class="nb">    a future release.</span><span class="o">)</span><span class="nb">  With this definition, {</span><span class="nv">\tt</span><span class="nb"> bagMax</span><span class="o">/</span><span class="m">2</span><span class="nb">} can be </span><span class="o">(</span><span class="nb">and</span>
</div><div id="l2122" class="code_block"><span class="nb">    is</span><span class="o">)</span><span class="nb"> defined as follows:</span>
</div><div id="l2123" class="code_block"><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l2124" class="code_block"><span class="nb">bagMax</span><span class="o">(</span><span class="nb">Call,Var</span><span class="o">)</span><span class="nb"> :</span><span class="o">-</span><span class="nb"> bagReduce</span><span class="o">(</span><span class="nb">Call,Var,maximum,_</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l2125" class="code_block"><span class="nv">\end</span><span class="nb">{verbatim}</span>
</div><div id="l2126" class="code_block"><span class="nb">    </span><span class="o">(</span><span class="nb">Where variables are minimal in the term ordering.</span><span class="o">)</span>
</div><div id="l2127" class="code_block">
</div><div id="l2128" class="code_block"><span class="nb">Another possible definition of {</span><span class="nv">\tt</span><span class="nb"> bagMax</span><span class="o">/</span><span class="m">2</span><span class="nb">} would be:</span>
</div><div id="l2129" class="code_block"><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l2130" class="code_block"><span class="nb">:</span><span class="o">-</span><span class="nb"> hilog lt.</span>
</div><div id="l2131" class="code_block"><span class="nb">lt</span><span class="o">(</span><span class="nb">X,Y</span><span class="o">)</span><span class="nb"> :</span><span class="o">-</span><span class="nb"> X @&lt; Y.</span>
</div><div id="l2132" class="code_block">
</div><div id="l2133" class="code_block"><span class="nb">bagMax</span><span class="o">(</span><span class="nb">Call,Var</span><span class="o">)</span><span class="nb"> :</span><span class="o">-</span><span class="nb"> bagPO</span><span class="o">(</span><span class="nb">Call,Var,lt</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l2134" class="code_block"><span class="nv">\end</span><span class="nb">{verbatim}</span>
</div><div id="l2135" class="code_block"><span class="nb">This definition would work, but it is slightly less efficient than the</span>
</div><div id="l2136" class="code_block"><span class="nb">previous definition since it is known that {</span><span class="nv">\tt</span><span class="nb"> bagMax} is</span>
</div><div id="l2137" class="code_block"><span class="nb">deterministic.</span>
</div><div id="l2138" class="code_block">
</div><div id="l2139" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{bagMin</span><span class="o">(</span><span class="nb">?SetPred,?Arg</span><span class="o">)</span><span class="nb">}{HiLog,Tabling}</span>
</div><div id="l2140" class="code_block"><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{bagMin</span><span class="o">/</span><span class="m">2</span><span class="nb">}}</span>
</div><div id="l2141" class="code_block">
</div><div id="l2142" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> SetPred} must be a HiLog set specification, i.e., a unary</span>
</div><div id="l2143" class="code_block"><span class="nb">    HiLog predicate.  {</span><span class="nv">\tt</span><span class="nb"> bagMin} returns with {</span><span class="nv">\tt</span><span class="nb"> Arg} bound to the</span>
</div><div id="l2144" class="code_block"><span class="nb">    minimum element </span><span class="o">(</span><span class="nb">under the Prolog term ordering</span><span class="o">)</span><span class="nb"> of the set {</span><span class="nv">\tt</span>
</div><div id="l2145" class="code_block"><span class="nb">    SetPred}.  To use this predicate, it must be imported from aggregs,</span>
</div><div id="l2146" class="code_block"><span class="nb">    and you must give the following definitions in the main module {</span><span class="nv">\tt</span>
</div><div id="l2147" class="code_block"><span class="nb">    usermod}:</span>
</div><div id="l2148" class="code_block"><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l2149" class="code_block"><span class="nb">:</span><span class="o">-</span><span class="nb"> hilog minimum.  </span>
</div><div id="l2150" class="code_block"><span class="nb">minimum</span><span class="o">(</span><span class="nb">X,Y,Z</span><span class="o">)</span><span class="nb"> :</span><span class="o">-</span><span class="nb"> X @&lt; Y </span><span class="o">-</span><span class="nb">&gt; Z</span><span class="o">=</span><span class="nb">X ; Z</span><span class="o">=</span><span class="nb">Y.</span>
</div><div id="l2151" class="code_block"><span class="nv">\end</span><span class="nb">{verbatim}</span>
</div><div id="l2152" class="code_block"><span class="nb">    </span><span class="o">(</span><span class="nb">These decarations are necessary because of a current limitation in</span>
</div><div id="l2153" class="code_block"><span class="nb">    how HiLog predicates can be used.  This requirement will be lifted in</span>
</div><div id="l2154" class="code_block"><span class="nb">    a future release.</span><span class="o">)</span><span class="nb">  With this definition, {</span><span class="nv">\tt</span><span class="nb"> bagMin</span><span class="o">/</span><span class="m">2</span><span class="nb">} can be </span><span class="o">(</span><span class="nb">and</span>
</div><div id="l2155" class="code_block"><span class="nb">    is</span><span class="o">)</span><span class="nb"> defined as:</span>
</div><div id="l2156" class="code_block"><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l2157" class="code_block"><span class="nb">bagMin</span><span class="o">(</span><span class="nb">Call,Var</span><span class="o">)</span><span class="nb"> :</span><span class="o">-</span><span class="nb"> bagReduce</span><span class="o">(</span><span class="nb">Call,Var,minimum,zz</span><span class="o">(</span><span class="nb">zz</span><span class="o">))</span><span class="nb">.</span>
</div><div id="l2158" class="code_block"><span class="nv">\end</span><span class="nb">{verbatim}</span>
</div><div id="l2159" class="code_block"><span class="nb">    </span><span class="o">(</span><span class="nb">where structures are the largest elements in the term ordering.</span><span class="o">)</span>
</div><div id="l2160" class="code_block">
</div><div id="l2161" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{bagSum</span><span class="o">(</span><span class="nb">?SetPred,?Arg</span><span class="o">)</span><span class="nb">}{HiLog,Tabling}</span>
</div><div id="l2162" class="code_block"><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{bagSum</span><span class="o">/</span><span class="m">2</span><span class="nb">}}</span>
</div><div id="l2163" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> SetPred} must be a HiLog set specification, i.e., a unary</span>
</div><div id="l2164" class="code_block"><span class="nb">    HiLog predicate.  {</span><span class="nv">\tt</span><span class="nb"> bagSum} returns with {</span><span class="nv">\tt</span><span class="nb"> Arg} bound to the sum</span>
</div><div id="l2165" class="code_block"><span class="nb">    of the elements of the set {</span><span class="nv">\tt</span><span class="nb"> SetPred}.  To use this predicate, it</span>
</div><div id="l2166" class="code_block"><span class="nb">    must be imported from aggregs, and you must give the following</span>
</div><div id="l2167" class="code_block"><span class="nb">    definitions in the main module {</span><span class="nv">\tt</span><span class="nb"> usermod}:</span>
</div><div id="l2168" class="code_block"><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l2169" class="code_block"><span class="nb">:</span><span class="o">-</span><span class="nb"> hilog sum.</span>
</div><div id="l2170" class="code_block"><span class="nb">sum</span><span class="o">(</span><span class="nb">X,Y,Z</span><span class="o">)</span><span class="nb"> :</span><span class="o">-</span><span class="nb"> Z is X</span><span class="o">+</span><span class="nb">Y.</span>
</div><div id="l2171" class="code_block"><span class="nv">\end</span><span class="nb">{verbatim}</span>
</div><div id="l2172" class="code_block"><span class="nb">    </span><span class="o">(</span><span class="nb">These decarations are necessary because of a current limitation in</span>
</div><div id="l2173" class="code_block"><span class="nb">    how HiLog predicates can be used.  This requirement will be lifted in</span>
</div><div id="l2174" class="code_block"><span class="nb">    a future release.</span><span class="o">)</span><span class="nb">  With this definition, {</span><span class="nv">\tt</span><span class="nb"> bagSum</span><span class="o">/</span><span class="m">2</span><span class="nb">} can be </span><span class="o">(</span><span class="nb">and</span>
</div><div id="l2175" class="code_block"><span class="nb">    is</span><span class="o">)</span><span class="nb"> defined as:</span>
</div><div id="l2176" class="code_block"><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l2177" class="code_block"><span class="nb">bagSum</span><span class="o">(</span><span class="nb">Call,Var</span><span class="o">)</span><span class="nb"> :</span><span class="o">-</span><span class="nb"> bagReduce</span><span class="o">(</span><span class="nb">Call,Var,sum,</span><span class="m">0</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l2178" class="code_block"><span class="nv">\end</span><span class="nb">{verbatim}</span>
</div><div id="l2179" class="code_block">
</div><div id="l2180" class="code_block"><span class="nv">\ouritem</span><span class="nb">{bagCount</span><span class="o">(</span><span class="nb">?SetPred,?Arg</span><span class="o">)</span><span class="nb">}{HiLog,Tabling}</span>
</div><div id="l2181" class="code_block"><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{bagCount</span><span class="o">/</span><span class="m">2</span><span class="nb">}}</span>
</div><div id="l2182" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> SetPred} must be a HiLog set specification, i.e., a unary</span>
</div><div id="l2183" class="code_block"><span class="nb">    HiLog predicate.  {</span><span class="nv">\tt</span><span class="nb"> bagCount} returns with {</span><span class="nv">\tt</span><span class="nb"> Arg} bound to the</span>
</div><div id="l2184" class="code_block"><span class="nb">    count </span><span class="o">(</span><span class="nb">i.e., number</span><span class="o">)</span><span class="nb"> of elements of the set {</span><span class="nv">\tt</span><span class="nb"> SetPred}.  To use</span>
</div><div id="l2185" class="code_block"><span class="nb">    this predicate, it must be imported from aggregs, and you must give</span>
</div><div id="l2186" class="code_block"><span class="nb">    the following definitions in the main module {</span><span class="nv">\tt</span><span class="nb"> usermod}:</span>
</div><div id="l2187" class="code_block"><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l2188" class="code_block"><span class="nb">:</span><span class="o">-</span><span class="nb"> hilog successor.</span>
</div><div id="l2189" class="code_block"><span class="nb">successor</span><span class="o">(</span><span class="nb">X,_Y,Z</span><span class="o">)</span><span class="nb"> :</span><span class="o">-</span><span class="nb"> Z is X</span><span class="o">+</span><span class="m">1</span><span class="nb">.</span>
</div><div id="l2190" class="code_block"><span class="nv">\end</span><span class="nb">{verbatim}</span>
</div><div id="l2191" class="code_block"><span class="nb">    </span><span class="o">(</span><span class="nb">These decarations are necessary because of a current limitation in</span>
</div><div id="l2192" class="code_block"><span class="nb">    how HiLog predicates can be used.  This requirement will be lifted in</span>
</div><div id="l2193" class="code_block"><span class="nb">    a future release.</span><span class="o">)</span><span class="nb">  With this definition, {</span><span class="nv">\tt</span><span class="nb"> bagCount</span><span class="o">/</span><span class="m">2</span><span class="nb">} can be </span><span class="o">(</span><span class="nb">and</span>
</div><div id="l2194" class="code_block"><span class="nb">    is</span><span class="o">)</span><span class="nb"> defined as:</span>
</div><div id="l2195" class="code_block"><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l2196" class="code_block"><span class="nb">bagCount</span><span class="o">(</span><span class="nb">Call,Var</span><span class="o">)</span><span class="nb"> :</span><span class="o">-</span><span class="nb"> bagReduce</span><span class="o">(</span><span class="nb">Call,Var,successor,</span><span class="m">0</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l2197" class="code_block"><span class="nv">\end</span><span class="nb">{verbatim}</span>
</div><div id="l2198" class="code_block">
</div><div id="l2199" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{bagAvg</span><span class="o">(</span><span class="nb">?SetPred,?Arg</span><span class="o">)</span><span class="nb">}{HiLog,Tabling}</span>
</div><div id="l2200" class="code_block"><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{bagAvg</span><span class="o">/</span><span class="m">2</span><span class="nb">}}</span>
</div><div id="l2201" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> SetPred} must be a HiLog set specification, i.e., a unary</span>
</div><div id="l2202" class="code_block"><span class="nb">    HiLog predicate.  {</span><span class="nv">\tt</span><span class="nb"> bagAvg} returns with {</span><span class="nv">\tt</span><span class="nb"> Arg} bound to the</span>
</div><div id="l2203" class="code_block"><span class="nb">    average </span><span class="o">(</span><span class="nb">i.e., mean</span><span class="o">)</span><span class="nb"> of elements of the set {</span><span class="nv">\tt</span><span class="nb"> SetPred}.  To use</span>
</div><div id="l2204" class="code_block"><span class="nb">    this predicate, it must be imported from aggregs, and you must give</span>
</div><div id="l2205" class="code_block"><span class="nb">    the following definitions in the main module {</span><span class="nv">\tt</span><span class="nb"> usermod}:</span>
</div><div id="l2206" class="code_block"><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l2207" class="code_block"><span class="nb">:</span><span class="o">-</span><span class="nb"> hilog sumcount.</span>
</div><div id="l2208" class="code_block"><span class="nb">sumcount</span><span class="o">([</span><span class="nb">S|C</span><span class="o">]</span><span class="nb">,X,</span><span class="o">[</span><span class="nb">S</span><span class="m">1</span><span class="nb">|C</span><span class="m">1</span><span class="o">])</span><span class="nb"> :</span><span class="o">-</span><span class="nb"> S</span><span class="m">1</span><span class="nb"> is S</span><span class="o">+</span><span class="nb">X, C</span><span class="m">1</span><span class="nb"> is C</span><span class="o">+</span><span class="m">1</span><span class="nb">.</span>
</div><div id="l2209" class="code_block"><span class="nv">\end</span><span class="nb">{verbatim}</span>
</div><div id="l2210" class="code_block"><span class="nb">    </span><span class="o">(</span><span class="nb">These decarations are necessary because of a current limitation in</span>
</div><div id="l2211" class="code_block"><span class="nb">    how HiLog predicates can be used.  This requirement will be lifted in</span>
</div><div id="l2212" class="code_block"><span class="nb">    a future release.</span><span class="o">)</span><span class="nb">  With this definition, {</span><span class="nv">\tt</span><span class="nb"> bagAvg</span><span class="o">/</span><span class="m">2</span><span class="nb">} can be </span><span class="o">(</span><span class="nb">and</span>
</div><div id="l2213" class="code_block"><span class="nb">    is</span><span class="o">)</span><span class="nb"> defined as:</span>
</div><div id="l2214" class="code_block"><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l2215" class="code_block"><span class="nb">bagAvg</span><span class="o">(</span><span class="nb">Call,Avg</span><span class="o">)</span><span class="nb"> :</span><span class="o">-</span><span class="nb"> </span>
</div><div id="l2216" class="code_block"><span class="nb">    bagReduce</span><span class="o">(</span><span class="nb">Call,</span><span class="o">[</span><span class="nb">Sum|Count</span><span class="o">]</span><span class="nb">,sumcount,</span><span class="o">[</span><span class="m">0</span><span class="nb">|</span><span class="m">0</span><span class="o">])</span><span class="nb">,</span>
</div><div id="l2217" class="code_block"><span class="nb">    Avg is Sum</span><span class="o">/</span><span class="nb">Count.</span>
</div><div id="l2218" class="code_block"><span class="nv">\end</span><span class="nb">{verbatim}</span>
</div><div id="l2219" class="code_block">
</div><div id="l2220" class="code_block"><span class="nv">\end</span><span class="nb">{description}</span>
</div><div id="l2221" class="code_block">
</div><div id="l2222" class="code_block"><span class="c">%-------------------------------------------------------------------------</span>
</div><div id="l2223" class="code_block"><span class="nv">\section</span><span class="nb">{Comparison} </span><span class="nv">\label</span><span class="nb">{Comparison}</span>
</div><div id="l2224" class="code_block"><span class="nv">\input</span><span class="nb">{comparison}</span>
</div><div id="l2225" class="code_block"><span class="c">%-------------------------------------------------------------------------</span>
</div><div id="l2226" class="code_block">
</div><div id="l2227" class="code_block"><span class="nv">\section</span><span class="nb">{Meta</span><span class="o">-</span><span class="nb">Predicates} </span><span class="nv">\label</span><span class="nb">{meta_predicates}</span>
</div><div id="l2228" class="code_block"><span class="nv">\begin</span><span class="nb">{description}</span>
</div><div id="l2229" class="code_block"><span class="nv">\ouritem</span><span class="nb">{call</span><span class="o">(</span><span class="nv">\#</span><span class="nb">X</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{call</span><span class="o">/</span><span class="m">1</span><span class="nb">}} </span>
</div><div id="l2230" class="code_block"><span class="c">%\predindex{call/1~(P)}</span>
</div><div id="l2231" class="code_block"><span class="nb">    If {</span><span class="nv">\tt</span><span class="nb"> X} is a nonvariable term in the program text, then it is </span>
</div><div id="l2232" class="code_block"><span class="nb">    executed exactly as if {</span><span class="nv">\tt</span><span class="nb"> X} appeared in the program text instead </span>
</div><div id="l2233" class="code_block"><span class="nb">    of {</span><span class="nv">\tt</span><span class="nb"> call</span><span class="o">(</span><span class="nb">X</span><span class="o">)</span><span class="nb">},</span>
</div><div id="l2234" class="code_block"><span class="nb">    e.g.</span>
</div><div id="l2235" class="code_block"><span class="nb">    </span><span class="nv">\begin</span><span class="nb">{center}</span>
</div><div id="l2236" class="code_block"><span class="nb">        {</span><span class="nv">\tt</span><span class="nb"> </span><span class="s">$</span><span class="k">\ldots</span><span class="s">$</span><span class="nb">, p</span><span class="o">(</span><span class="nb">a</span><span class="o">)</span><span class="nb">, call</span><span class="o">(</span><span class="nb"> </span><span class="o">(</span><span class="nb">q</span><span class="o">(</span><span class="nb">X</span><span class="o">)</span><span class="nb">, r</span><span class="o">(</span><span class="nb">Y</span><span class="o">))</span><span class="nb"> </span><span class="o">)</span><span class="nb">, s</span><span class="o">(</span><span class="nb">X</span><span class="o">)</span><span class="nb">, </span><span class="s">$</span><span class="k">\ldots</span><span class="s">$</span><span class="nb">}</span>
</div><div id="l2237" class="code_block"><span class="nb">    </span><span class="nv">\end</span><span class="nb">{center}</span>
</div><div id="l2238" class="code_block"><span class="nb">    is equivalent to</span>
</div><div id="l2239" class="code_block"><span class="nb">    </span><span class="nv">\begin</span><span class="nb">{center}</span>
</div><div id="l2240" class="code_block"><span class="nb">        {</span><span class="nv">\tt</span><span class="nb"> </span><span class="s">$</span><span class="k">\ldots</span><span class="s">$</span><span class="nb">, p</span><span class="o">(</span><span class="nb">a</span><span class="o">)</span><span class="nb">, q</span><span class="o">(</span><span class="nb">X</span><span class="o">)</span><span class="nb">, r</span><span class="o">(</span><span class="nb">Y</span><span class="o">)</span><span class="nb">, s</span><span class="o">(</span><span class="nb">X</span><span class="o">)</span><span class="nb">, </span><span class="s">$</span><span class="k">\ldots</span><span class="s">$</span><span class="nb">}</span>
</div><div id="l2241" class="code_block"><span class="nb">    </span><span class="nv">\end</span><span class="nb">{center}</span>
</div><div id="l2242" class="code_block"><span class="nb">    However, if {</span><span class="nv">\tt</span><span class="nb"> X} is a variable in the program text,</span>
</div><div id="l2243" class="code_block"><span class="nb">    then if at runtime {</span><span class="nv">\tt</span><span class="nb"> X} is instantiated to a term which </span>
</div><div id="l2244" class="code_block"><span class="nb">    would be acceptable as the body of a clause, the goal </span>
</div><div id="l2245" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> call</span><span class="o">(</span><span class="nb">X</span><span class="o">)</span><span class="nb">} is executed as if that</span>
</div><div id="l2246" class="code_block"><span class="nb">    term appeared textually in place of the {</span><span class="nv">\tt</span><span class="nb"> call</span><span class="o">(</span><span class="nb">X</span><span class="o">)</span><span class="nb">},</span>
</div><div id="l2247" class="code_block"><span class="nb">    {</span><span class="nv">\em</span><span class="nb"> except that} any cut </span><span class="o">(</span><span class="nb">`</span><span class="o">!</span><span class="nb">&#39;</span><span class="o">)</span><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{&quot;</span><span class="o">!/</span><span class="m">0</span><span class="nb">}}</span><span class="nv">\index</span><span class="nb">{cut}</span>
</div><div id="l2248" class="code_block"><span class="nb">    occurring in {</span><span class="nv">\tt</span><span class="nb"> X} will remove only those choice points in~{</span><span class="nv">\tt</span><span class="nb"> X}.</span>
</div><div id="l2249" class="code_block"><span class="nb">    If~{</span><span class="nv">\tt</span><span class="nb"> X} is not instantiated as described above,</span>
</div><div id="l2250" class="code_block"><span class="nb">    an error message is printed and {</span><span class="nv">\tt</span><span class="nb"> call</span><span class="o">/</span><span class="m">1</span><span class="nb">} fails.</span>
</div><div id="l2251" class="code_block">
</div><div id="l2252" class="code_block"><span class="nb">    Exceptions:</span>
</div><div id="l2253" class="code_block"><span class="nb">    </span><span class="nv">\begin</span><span class="nb">{description}</span>
</div><div id="l2254" class="code_block"><span class="nb">    </span><span class="nv">\item</span><span class="o">[</span><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> instantiation</span><span class="nv">\_</span><span class="nb">error}</span><span class="o">]</span>
</div><div id="l2255" class="code_block"><span class="nb">	Argument </span><span class="m">1</span><span class="nb"> of {</span><span class="nv">\tt</span><span class="nb"> call</span><span class="o">/</span><span class="m">1</span><span class="nb">} is not instantiated.</span>
</div><div id="l2256" class="code_block"><span class="nb">     </span><span class="nv">\item</span><span class="o">[</span><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> type</span><span class="nv">\_</span><span class="nb">error}</span><span class="o">]</span>
</div><div id="l2257" class="code_block"><span class="nb">	Argument </span><span class="m">1</span><span class="nb"> of {</span><span class="nv">\tt</span><span class="nb"> call</span><span class="o">/</span><span class="m">1</span><span class="nb">} is not a callable term.</span>
</div><div id="l2258" class="code_block"><span class="nb">    </span><span class="nv">\end</span><span class="nb">{description}</span>
</div><div id="l2259" class="code_block">
</div><div id="l2260" class="code_block"><span class="nv">\ouritem</span><span class="nb">{</span><span class="nv">\#</span><span class="nb">X}					      </span>
</div><div id="l2261" class="code_block"><span class="nb">    </span><span class="o">(</span><span class="nb">where {</span><span class="nv">\tt</span><span class="nb"> X} is a variable</span><span class="o">)</span><span class="nb"> executes exactly the same as </span>
</div><div id="l2262" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> call</span><span class="o">(</span><span class="nb">X</span><span class="o">)</span><span class="nb">}.</span>
</div><div id="l2263" class="code_block"><span class="nb">    However, the explicit use of {</span><span class="nv">\tt</span><span class="nb"> call</span><span class="o">/</span><span class="m">1</span><span class="nb">} is considered better</span>
</div><div id="l2264" class="code_block"><span class="nb">    programming practice.  The use of a top level variable subgoal</span>
</div><div id="l2265" class="code_block"><span class="nb">    elicits a warning from the compiler.</span>
</div><div id="l2266" class="code_block">
</div><div id="l2267" class="code_block"><span class="nv">\ouritem</span><span class="nb">{once</span><span class="o">(</span><span class="nv">\#</span><span class="nb">X</span><span class="o">)</span><span class="nb">}</span>
</div><div id="l2268" class="code_block"><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{once</span><span class="o">/</span><span class="m">1</span><span class="nb">}} </span>
</div><div id="l2269" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> once</span><span class="o">/</span><span class="m">1</span><span class="nb">} is defined as {</span><span class="nv">\tt</span><span class="nb"> once</span><span class="o">(</span><span class="nb">X</span><span class="o">)</span><span class="nb">:</span><span class="o">-</span><span class="nb"> call</span><span class="o">(</span><span class="nb">X</span><span class="o">)</span><span class="nb">,</span><span class="o">!</span><span class="nb">.}  {</span><span class="nv">\tt</span>
</div><div id="l2270" class="code_block"><span class="nb">    once</span><span class="o">/</span><span class="m">1</span><span class="nb">} should be used with care in tabled programs.  The compiler</span>
</div><div id="l2271" class="code_block"><span class="nb">    can not determine whether a tabled predicate is called in the</span>
</div><div id="l2272" class="code_block"><span class="nb">    scope of {</span><span class="nv">\tt</span><span class="nb"> once</span><span class="o">/</span><span class="m">1</span><span class="nb">}, and such a call may lead to runtime errors.</span>
</div><div id="l2273" class="code_block"><span class="nb">    If a tabled predicate may occur in the scope of {</span><span class="nv">\tt</span><span class="nb"> once</span><span class="o">/</span><span class="m">1</span><span class="nb">}, use</span>
</div><div id="l2274" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> table</span><span class="nv">\_</span><span class="nb">once</span><span class="o">/</span><span class="m">1</span><span class="nb">} instead.</span>
</div><div id="l2275" class="code_block">
</div><div id="l2276" class="code_block"><span class="nb">    Exceptions: The same as {</span><span class="nv">\tt</span><span class="nb"> call</span><span class="o">/</span><span class="m">1</span><span class="nb">}.</span>
</div><div id="l2277" class="code_block">
</div><div id="l2278" class="code_block"><span class="nv">\ouritem</span><span class="nb">{table</span><span class="nv">\_</span><span class="nb">once</span><span class="o">(</span><span class="nv">\#</span><span class="nb">X</span><span class="o">)</span><span class="nb">}</span>
</div><div id="l2279" class="code_block"><span class="nv">\index</span><span class="nb">{</span><span class="nv">\texttt</span><span class="nb">{table</span><span class="nv">\_</span><span class="nb">once</span><span class="o">/</span><span class="m">1</span><span class="nb">}} </span>
</div><div id="l2280" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> table</span><span class="nv">\_</span><span class="nb">once</span><span class="o">/</span><span class="m">1</span><span class="nb">} is a weaker form of {</span><span class="nv">\tt</span><span class="nb"> once</span><span class="o">/</span><span class="m">1</span><span class="nb">}, suitable for</span>
</div><div id="l2281" class="code_block"><span class="nb">    situations in which a single solution is desired for a</span>
</div><div id="l2282" class="code_block"><span class="nb">    subcomputation that may involve a call to a tabled predicate.  {</span><span class="nv">\tt</span>
</div><div id="l2283" class="code_block"><span class="nb">    table</span><span class="nv">\_</span><span class="nb">once</span><span class="o">(</span><span class="nb">?Pred</span><span class="o">)</span><span class="nb">} succeeds only once even if there are many</span>
</div><div id="l2284" class="code_block"><span class="nb">    solutions to the subgoal {</span><span class="nv">\tt</span><span class="nb"> Pred}.  However, it does not ``cut</span>
</div><div id="l2285" class="code_block"><span class="nb">    over&#39;&#39; the subcomputation started by the subgoal {</span><span class="nv">\tt</span><span class="nb"> Pred},</span>
</div><div id="l2286" class="code_block"><span class="nb">    thereby ensuring the correct evaluation of tabled subgoals.</span>
</div><div id="l2287" class="code_block">
</div><div id="l2288" class="code_block"><span class="nv">\end</span><span class="nb">{description}</span>
</div><div id="l2289" class="code_block">
</div><div id="l2290" class="code_block">
</div><div id="l2291" class="code_block"><span class="c">%%% Local Variables: </span>
</div><div id="l2292" class="code_block"><span class="c">%%% mode: latex</span>
</div><div id="l2293" class="code_block"><span class="c">%%% TeX-master: &quot;manual1&quot;</span>
</div><div id="l2294" class="code_block"><span class="c">%%% End: </span>
</div></pre></div></td></tr></table></div>

      
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