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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">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></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">Presently, input and output can only be done with respect to the 
</div><div id="l15" class="code_block">current input and output
</div><div id="l16" class="code_block">streams.  These can be set, reset or checked using the file handling
</div><div id="l17" class="code_block">predicates described below.  The default input and output streams are
</div><div id="l18" class="code_block">internally denoted by userin and userout (the user accesses them both 
</div><div id="l19" class="code_block">via the name <span class="nb">{</span><span class="k">\tt</span> ``user&#39;&#39;<span class="nb">}</span>, and they refer to the user&#39;s terminal).
</div><div id="l20" class="code_block">
</div><div id="l21" class="code_block">
</div><div id="l22" class="code_block"><span class="k">\subsection</span><span class="nb">{</span>File Handling<span class="nb">}</span>
</div><div id="l23" class="code_block"><span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l24" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>set<span class="k">\_input</span>(+F)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> set<span class="k">\_input</span>/1<span class="nb">}}</span>
</div><div id="l25" class="code_block"><span class="k">\vspace</span><span class="nb">{</span>-7mm<span class="nb">}</span> 
</div><div id="l26" 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">\tt</span> see/1<span class="nb">}}</span>
</div><div id="l27" 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="l28" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l29" class="code_block">    <span class="k">\item</span> If there is an open input stream associated with the file that 
</div><div id="l30" 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="l31" 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="l32" class="code_block">    <span class="k">\item</span> Otherwise, the specified file is opened for input and made the
</div><div id="l33" 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="l34" class="code_block">	  fails.
</div><div id="l35" class="code_block">    <span class="k">\end</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l36" class="code_block">    Also note that different file names (that is, names which do not unify) 
</div><div id="l37" class="code_block">    represent different input streams (even if these different file names 
</div><div id="l38" class="code_block">    correspond to the same file).
</div><div id="l39" class="code_block">
</div><div id="l40" class="code_block">    Exceptions:
</div><div id="l41" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l42" class="code_block">    <span class="k">\item</span><span class="na">[{\tt permission\_error}]</span>
</div><div id="l43" 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="l44" class="code_block">    <span class="k">\item</span><span class="na">[{\tt instantiation\_error}]</span>
</div><div id="l45" 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="l46" class="code_block">    <span class="k">\item</span><span class="na">[{\tt existence\_error}]</span>
</div><div id="l47" class="code_block">    	File <span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> does not exist. 
</div><div id="l48" class="code_block">    <span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l49" class="code_block">
</div><div id="l50" 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">\tt</span> seeing/1<span class="nb">}}</span>
</div><div id="l51" 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="l52" 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="l53" 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="l54" class="code_block">    upwards compatibility reasons.
</div><div id="l55" class="code_block">
</div><div id="l56" 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">\tt</span> seen/0<span class="nb">}}</span>
</div><div id="l57" class="code_block">    Closes the current input stream. 
</div><div id="l58" 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="l59" class="code_block">
</div><div id="l60" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>set<span class="k">\_output</span>(+F)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> set<span class="k">\_output</span>/1<span class="nb">}}</span>
</div><div id="l61" class="code_block"><span class="k">\vspace</span><span class="nb">{</span>-7mm<span class="nb">}</span> 
</div><div id="l62" 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">\tt</span> tell/1<span class="nb">}}</span>
</div><div id="l63" 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="l64" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l65" 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="l66" class="code_block">          and that was opened previously 
</div><div id="l67" 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="l68" class="code_block">	  stream. 
</div><div id="l69" class="code_block">    <span class="k">\item</span> Otherwise, the specified file is opened for output and made the
</div><div id="l70" class="code_block">          current output stream. If the file does not exist, it is created.
</div><div id="l71" class="code_block">    <span class="k">\end</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l72" class="code_block">
</div><div id="l73" class="code_block">    Also note that different file names (that is, names which do not unify) 
</div><div id="l74" class="code_block">    represent different output streams (even if these different file names 
</div><div id="l75" class="code_block">    correspond to the same file).
</div><div id="l76" class="code_block">
</div><div id="l77" class="code_block">    Exceptions:
</div><div id="l78" class="code_block">    <span class="k">\begin</span> <span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l79" class="code_block">    <span class="k">\item</span><span class="na">[{\tt permission\_error}]</span>
</div><div id="l80" 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="l81" class="code_block">    <span class="k">\item</span><span class="na">[{\tt instantiation\_error}]</span>
</div><div id="l82" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> is uninstantiated.
</div><div id="l83" class="code_block">    <span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l84" class="code_block">
</div><div id="l85" 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">\tt</span> telling/1<span class="nb">}}</span>
</div><div id="l86" 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="l87" 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="l88" 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="l89" class="code_block">    upwards compatibility reasons.
</div><div id="l90" class="code_block">
</div><div id="l91" 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">\tt</span> told/0<span class="nb">}}</span>
</div><div id="l92" class="code_block">    Closes the current output stream. 
</div><div id="l93" class="code_block">    Current output stream reverts to ``userout&#39;&#39; (the standard output stream).
</div><div id="l94" class="code_block">
</div><div id="l95" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>open(+File,+Mode,-Stream)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> close/1<span class="nb">}}</span>
</div><div id="l96" 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="l97" 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="l98" 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="l99" 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="l100" 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="l101" 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="l102" 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="l103" class="code_block">    contents of <span class="nb">{</span><span class="k">\em</span> File<span class="nb">}</span>.
</div><div id="l104" class="code_block">
</div><div id="l105" class="code_block">    Exceptions (<span class="nb">{</span><span class="k">\tt</span> read<span class="nb">}</span> mode)
</div><div id="l106" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l107" class="code_block">    <span class="k">\item</span><span class="na">[{\tt permission\_error}]</span>
</div><div id="l108" 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="l109" class="code_block">    <span class="k">\item</span><span class="na">[{\tt instantiation\_error}]</span>
</div><div id="l110" 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="l111" class="code_block">    <span class="k">\item</span><span class="na">[{\tt existence\_error}]</span>
</div><div id="l112" class="code_block">    	File <span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> does not exist. 
</div><div id="l113" class="code_block">    <span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l114" class="code_block">
</div><div id="l115" class="code_block">    Exceptions (<span class="nb">{</span><span class="k">\tt</span> write<span class="nb">}</span> mode)
</div><div id="l116" class="code_block">    <span class="k">\begin</span> <span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l117" class="code_block">    <span class="k">\item</span><span class="na">[{\tt permission\_error}]</span>
</div><div id="l118" 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="l119" class="code_block">    <span class="k">\item</span><span class="na">[{\tt instantiation\_error}]</span>
</div><div id="l120" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> is uninstantiated.
</div><div id="l121" class="code_block">    <span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l122" class="code_block">
</div><div id="l123" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>close(+Stream)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> close/1<span class="nb">}}</span>
</div><div id="l124" 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="l125" class="code_block">
</div><div id="l126" 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">\tt</span> file<span class="k">\_exists</span>/1<span class="nb">}}</span>
</div><div id="l127" 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="l128" class="code_block">    an atom at the time of the call, or an error message is displayed on
</div><div id="l129" class="code_block">    the standard error stream and the predicate aborts.
</div><div id="l130" class="code_block">
</div><div id="l131" class="code_block">    Exceptions:
</div><div id="l132" class="code_block">    <span class="k">\begin</span> <span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l133" class="code_block">    <span class="k">\item</span><span class="na">[{\tt instantiation\_error}]</span>
</div><div id="l134" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> is uninstantiated.
</div><div id="l135" class="code_block">    <span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l136" class="code_block">
</div><div id="l137" class="code_block"><span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l138" class="code_block">
</div><div id="l139" class="code_block">
</div><div id="l140" class="code_block"><span class="k">\subsection</span><span class="nb">{</span>Character I/O<span class="nb">}</span>
</div><div id="l141" class="code_block"><span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l142" 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">\tt</span> nl/0<span class="nb">}}</span>
</div><div id="l143" class="code_block">    A new line character is sent to the current output stream.
</div><div id="l144" class="code_block">
</div><div id="l145" 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">\tt</span> nl/1<span class="nb">}}</span>
</div><div id="l146" class="code_block">    A new line character is sent to the designated output stream.
</div><div id="l147" class="code_block">
</div><div id="l148" 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">\tt</span> get0/1<span class="nb">}}</span> 
</div><div id="l149" 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="l150" class="code_block">    current input stream (regarded as a text stream). If the current
</div><div id="l151" 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="l152" class="code_block">
</div><div id="l153" class="code_block">    Compatibility Note:  Unlike other Prologs, such as C-Prolog, the input 
</div><div id="l154" class="code_block">    stream is not closed on encountering the end-of-file character.
</div><div id="l155" class="code_block">
</div><div id="l156" 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">\tt</span> get/1<span class="nb">}}</span> 
</div><div id="l157" 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="l158" class="code_block">    character from the current input stream (regarded as a text
</div><div id="l159" class="code_block">    stream).  If the current input stream reaches its end of file, a
</div><div id="l160" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> -1<span class="nb">}</span> is returned.
</div><div id="l161" class="code_block">
</div><div id="l162" class="code_block">    Compatibility Note:  Unlike other Prologs, such as C-Prolog, the input 
</div><div id="l163" class="code_block">    stream is not closed on encountering the end-of-file character.
</div><div id="l164" class="code_block">
</div><div id="l165" 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">\tt</span> get<span class="k">\_code</span>/1<span class="nb">}}</span>
</div><div id="l166" class="code_block"><span class="k">\vspace</span><span class="nb">{</span>-7mm<span class="nb">}</span> 
</div><div id="l167" 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">\tt</span> get<span class="k">\_code</span>/2<span class="nb">}}</span>
</div><div id="l168" 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="l169" 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="l170" 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="l171" class="code_block">   all cases to the ISO standard.
</div><div id="l172" class="code_block">
</div><div id="l173" 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">\tt</span> get<span class="k">\_char</span>/1<span class="nb">}}</span>
</div><div id="l174" class="code_block"><span class="k">\vspace</span><span class="nb">{</span>-7mm<span class="nb">}</span> 
</div><div id="l175" 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">\tt</span> get<span class="k">\_char</span>/2<span class="nb">}}</span>
</div><div id="l176" 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="l177" 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="l178" 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="l179" class="code_block">   standard.
</div><div id="l180" class="code_block">
</div><div id="l181" 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">\tt</span> put/1<span class="nb">}}</span>
</div><div id="l182" 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="l183" class="code_block">
</div><div id="l184" class="code_block">    Exceptions:
</div><div id="l185" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l186" class="code_block">    <span class="k">\item</span><span class="na">[{\tt instantiation\_error}]</span>
</div><div id="l187" 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="l188" class="code_block">    <span class="k">\item</span><span class="na">[{\tt type\_error}]</span>
</div><div id="l189" 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="l190" class="code_block">    <span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l191" class="code_block">
</div><div id="l192" 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">\tt</span> put<span class="k">\_code</span>/1<span class="nb">}}</span>
</div><div id="l193" class="code_block"><span class="k">\vspace</span><span class="nb">{</span>-7mm<span class="nb">}</span> 
</div><div id="l194" 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">\tt</span> put<span class="k">\_code</span>/2<span class="nb">}}</span>
</div><div id="l195" 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="l196" 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="l197" 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="l198" class="code_block">    standard.
</div><div id="l199" class="code_block">
</div><div id="l200" 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">\tt</span> put<span class="k">\_char</span>/1<span class="nb">}}</span>
</div><div id="l201" class="code_block"><span class="k">\vspace</span><span class="nb">{</span>-7mm<span class="nb">}</span> 
</div><div id="l202" 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">\tt</span> put<span class="k">\_char</span>/2<span class="nb">}}</span>
</div><div id="l203" 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="l204" 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="l205" 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="l206" class="code_block">    all cases to the ISO standard.
</div><div id="l207" class="code_block">
</div><div id="l208" class="code_block">
</div><div id="l209" 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">\tt</span> tab/1<span class="nb">}}</span>
</div><div id="l210" 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="l211" class="code_block">
</div><div id="l212" class="code_block">    Exceptions:
</div><div id="l213" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l214" class="code_block">    <span class="k">\item</span><span class="na">[{\tt instantiation\_error}]</span>
</div><div id="l215" 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="l216" class="code_block">    <span class="k">\item</span><span class="na">[{\tt type\_error}]</span>
</div><div id="l217" 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="l218" class="code_block">    <span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l219" class="code_block"><span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l220" class="code_block">
</div><div id="l221" class="code_block"><span class="k">\subsection</span><span class="nb">{</span>Term I/O<span class="nb">}</span>
</div><div id="l222" class="code_block"><span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l223" 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">\tt</span> read/1<span class="nb">}}</span>
</div><div id="l224" class="code_block">    A HiLog term is read from the current or designated input stream,
</div><div id="l225" 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="l226" 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="l227" class="code_block">    syntax of HiLog terms). The term must be delimited by a full stop
</div><div id="l228" class="code_block">    (i.e. a ``.&#39;&#39; followed by a carriage-return, space or tab).
</div><div id="l229" 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="l230" 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="l231" class="code_block">    read/1<span class="nb">}</span> does not fail but continues reading terms until a term
</div><div id="l232" 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="l233" class="code_block">    read(Term)<span class="nb">}</span> causes the end of the current input stream to be
</div><div id="l234" 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="l235" 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="l236" class="code_block">    the same input stream will cause an error failure.
</div><div id="l237" class="code_block">
</div><div id="l238" class="code_block">    Exceptions:
</div><div id="l239" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l240" class="code_block">    <span class="k">\item</span><span class="na">[{\tt existence\_error}]</span>
</div><div id="l241" 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="l242" class="code_block">    <span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l243" class="code_block">
</div><div id="l244" 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">\tt</span> read/2<span class="nb">}}</span>
</div><div id="l245" 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="l246" class="code_block">	input stream is explicitly designated using the first argument.
</div><div id="l247" class="code_block">
</div><div id="l248" 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">\tt</span> write/1<span class="nb">}}</span>
</div><div id="l249" 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="l250" class="code_block">    according to the operator declarations in force.  Any uninstantiated 
</div><div id="l251" 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="l252" class="code_block">    underscore followed by a non-negative integer).  
</div><div id="l253" class="code_block">
</div><div id="l254" 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="l255" class="code_block">    are not written in their internal Prolog representation.  Predicate 
</div><div id="l256" 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="l257" class="code_block">
</div><div id="l258" 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="l259" 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="l260" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l261" 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="l262" 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="l263" 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="l264" class="code_block">          whenever necessary.
</div><div id="l265" 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="l266" class="code_block">          therefore, if the user wants the term to be accepted as input to
</div><div id="l267" 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="l268" class="code_block">          to the current output stream. 
</div><div id="l269" class="code_block">    <span class="k">\end</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l270" class="code_block">
</div><div id="l271" class="code_block">    Predicate <span class="nb">{</span><span class="k">\tt</span> write/1<span class="nb">}</span> treats terms of the form 
</div><div id="l272" class="code_block">    <span class="k">\verb</span>|&#39;<span class="s">$</span><span class="nb">VAR&#39;</span><span class="o">(</span><span class="nb">N</span><span class="o">)</span><span class="nb">| specially:  it writes {</span><span class="nv">\tt</span><span class="nb"> &#39;A&#39;} if {</span><span class="nv">\tt</span><span class="nb"> N}</span><span class="o">=</span><span class="m">0</span><span class="nb">,</span>
</div><div id="l273" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> &#39;B&#39;} if {</span><span class="nv">\tt</span><span class="nb"> N}</span><span class="o">=</span><span class="m">1</span><span class="nb">, </span><span class="s">$</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;} </span>
</div><div id="l274" class="code_block"><span class="nb">    if {</span><span class="nv">\tt</span><span class="nb"> N}</span><span class="o">=</span><span class="m">26</span><span class="nb">, etc.  Terms of this form are generated by</span>
</div><div id="l275" class="code_block"><span class="nb">    {</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">} 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="l276" class="code_block"><span class="c">%% $</span>
</div><div id="l277" class="code_block">
</div><div id="l278" class="code_block"><span class="nv">\ouritem</span><span class="nb">{write</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">\tt</span><span class="nb"> write</span><span class="o">/</span><span class="m">2</span><span class="nb">}}</span>
</div><div id="l279" class="code_block"><span class="nb">	{</span><span class="nv">\tt</span><span class="nb"> write</span><span class="o">/</span><span class="m">2</span><span class="nb">} has the same behavior as {</span><span class="nv">\tt</span><span class="nb"> write</span><span class="o">/</span><span class="m">1</span><span class="nb">} but the</span>
</div><div id="l280" class="code_block"><span class="nb">	output stream is explicitly designated using the first argument.</span>
</div><div id="l281" class="code_block">
</div><div id="l282" class="code_block"><span class="nv">\ouritem</span><span class="nb">{write</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">Options</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{{</span><span class="nv">\tt</span><span class="nb"> write</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="l283" class="code_block"><span class="nv">\vspace</span><span class="nb">{</span><span class="o">-</span><span class="m">7</span><span class="nb">mm} </span>
</div><div id="l284" class="code_block"><span class="nv">\ouritem</span><span class="nb">{write</span><span class="nv">\_</span><span class="nb">term</span><span class="o">(+</span><span class="nb">Stream, ?Term,</span><span class="o">+</span><span class="nb">Options</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><span class="nb">{{</span><span class="nv">\tt</span><span class="nb"> write</span><span class="nv">\_</span><span class="nb">term</span><span class="o">/</span><span class="m">3</span><span class="nb">}}</span>
</div><div id="l285" class="code_block">
</div><div id="l286" class="code_block"><span class="nb">    Outputs {</span><span class="nv">\tt</span><span class="nb"> </span><span class="o">+</span><span class="nb">Term} to the current output </span><span class="o">(</span><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> write</span><span class="nv">\_</span><span class="nb">term</span><span class="o">/</span><span class="m">2</span><span class="nb">}</span><span class="o">)</span><span class="nb"> or</span>
</div><div id="l287" class="code_block"><span class="nb">    to {</span><span class="nv">\tt</span><span class="nb"> Stream} </span><span class="o">(</span><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> write</span><span class="nv">\_</span><span class="nb">term</span><span class="o">/</span><span class="m">3</span><span class="nb">}</span><span class="o">)</span><span class="nb"> according to the list of</span>
</div><div id="l288" class="code_block"><span class="nb">    write options, {</span><span class="nv">\tt</span><span class="nb"> Options}.  The current set of write options</span>
</div><div id="l289" class="code_block"><span class="nb">    which form a superset of the ISO</span><span class="o">-</span><span class="nb">standard write options, are as</span>
</div><div id="l290" class="code_block"><span class="nb">    follows:</span>
</div><div id="l291" class="code_block"><span class="c">%</span>
</div><div id="l292" class="code_block"><span class="nv">\begin</span><span class="nb">{itemize}</span>
</div><div id="l293" class="code_block"><span class="c">%</span>
</div><div id="l294" class="code_block"><span class="nv">\item</span><span class="nb"> {</span><span class="nv">\tt</span><span class="nb"> quoted</span><span class="o">(+</span><span class="nb">Bool</span><span class="o">)</span><span class="nb">}.  If {</span><span class="nv">\tt</span><span class="nb"> Bool </span><span class="o">=</span><span class="nb"> true}, then atoms and</span>
</div><div id="l295" class="code_block"><span class="nb">    functors that can&#39;t be read back by {</span><span class="nv">\tt</span><span class="nb"> read</span><span class="o">/</span><span class="m">1</span><span class="nb">} are quoted, if</span>
</div><div id="l296" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> Bool </span><span class="o">=</span><span class="nb"> false}, each atom and functor is written as its</span>
</div><div id="l297" class="code_block"><span class="nb">    unquoted name. Default value is {</span><span class="nv">\tt</span><span class="nb"> false}.</span>
</div><div id="l298" class="code_block"><span class="c">%</span>
</div><div id="l299" class="code_block"><span class="nv">\item</span><span class="nb"> {</span><span class="nv">\tt</span><span class="nb"> ignore</span><span class="nv">\_</span><span class="nb">ops</span><span class="o">(+</span><span class="nb">Bool</span><span class="o">)</span><span class="nb">}. If {</span><span class="nv">\tt</span><span class="nb"> Bool </span><span class="o">=</span><span class="nb"> true} each compound term</span>
</div><div id="l300" class="code_block"><span class="nb">is output in functional notation; curly brackets and list braces are</span>
</div><div id="l301" class="code_block"><span class="nb">ignored, as are all explicitly defined operators.  If {</span><span class="nv">\tt</span><span class="nb"> Bool </span><span class="o">=</span>
</div><div id="l302" class="code_block"><span class="nb">false}, curly bracketed notation and list notation is enabled when</span>
</div><div id="l303" class="code_block"><span class="nb">outputing compound terms, and all other operator notation is</span>
</div><div id="l304" class="code_block"><span class="nb">enabed.  Default value is {</span><span class="nv">\tt</span><span class="nb"> false}.</span>
</div><div id="l305" class="code_block"><span class="c">%</span>
</div><div id="l306" class="code_block"><span class="nb"> </span><span class="nv">\item</span><span class="nb"> {</span><span class="nv">\tt</span><span class="nb"> numbervars</span><span class="o">(+</span><span class="nb">Bool</span><span class="o">)</span><span class="nb">}.  If {</span><span class="nv">\tt</span><span class="nb"> Bool </span><span class="o">=</span><span class="nb"> true}, a term of the</span>
</div><div id="l307" class="code_block"><span class="nb">form {</span><span class="nv">\tt</span><span class="nb"> &#39;</span><span class="nv">\$</span><span class="nb">VAR&#39;</span><span class="o">(</span><span class="nb">N</span><span class="o">)</span><span class="nb">} where {</span><span class="nv">\tt</span><span class="nb"> N} is an integer, is output as a</span>
</div><div id="l308" class="code_block"><span class="nb">variable name consisting of a capital letter possibly followed by an</span>
</div><div id="l309" class="code_block"><span class="nb">integer.  A term of the form {</span><span class="nv">\tt</span><span class="nb"> &#39;</span><span class="nv">\$</span><span class="nb">VAR&#39;</span><span class="o">(</span><span class="nb">Atom</span><span class="o">)</span><span class="nb">} where {</span><span class="nv">\tt</span><span class="nb"> Atom} is an</span>
</div><div id="l310" class="code_block"><span class="nb">atom, is output as itself </span><span class="o">(</span><span class="nb">without quotes</span><span class="o">)</span><span class="nb">.  Finally, a term of the</span>
</div><div id="l311" class="code_block"><span class="nb">form {</span><span class="nv">\tt</span><span class="nb"> &#39;</span><span class="nv">\$</span><span class="nb">VAR&#39;</span><span class="o">(</span><span class="nb">String</span><span class="o">)</span><span class="nb">} where {</span><span class="nv">\tt</span><span class="nb"> String} is a character string, is</span>
</div><div id="l312" class="code_block"><span class="nb">output as the atom corresponding to this character string.  If</span>
</div><div id="l313" class="code_block"><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> bool} is {</span><span class="nv">\tt</span><span class="nb"> false} this cases are not treated in any special</span>
</div><div id="l314" class="code_block"><span class="nb">way.  Default value is {</span><span class="nv">\tt</span><span class="nb"> false}.</span>
</div><div id="l315" class="code_block"><span class="c">%</span>
</div><div id="l316" class="code_block"><span class="c">% See predicates {\tt numbervars/3} and {\tt prettyvars/1}.  </span>
</div><div id="l317" class="code_block"><span class="c">%</span>
</div><div id="l318" class="code_block"><span class="c">% TLS: need predicate portray attribute, if we dont have it.</span>
</div><div id="l319" class="code_block"><span class="c">%</span>
</div><div id="l320" class="code_block"><span class="nv">\comment</span><span class="nb">{</span>
</div><div id="l321" class="code_block"><span class="nv">\item</span><span class="nb"> {</span><span class="nv">\tt</span><span class="nb"> portrayed</span><span class="o">(+</span><span class="nb">Bool</span><span class="o">)</span><span class="nb">}. If {</span><span class="nv">\tt</span><span class="nb"> Bool </span><span class="o">=</span><span class="nb"> true}, then a call is made</span>
</div><div id="l322" class="code_block"><span class="nb">to the predicate @pred{portray</span><span class="o">/</span><span class="m">1</span><span class="nb">}, to</span>
</div><div id="l323" class="code_block"><span class="nb">provide the user handlers for pretty printing some terms.  {</span><span class="nv">\tt</span>
</div><div id="l324" class="code_block"><span class="nb">portray_attribute</span><span class="o">/</span><span class="m">1</span><span class="nb">} is called whenever an attributed variable is to</span>
</div><div id="l325" class="code_block"><span class="nb">be printed, {</span><span class="nv">\tt</span><span class="nb"> portray</span><span class="o">/</span><span class="m">1</span><span class="nb">} is called whenever a non</span><span class="o">-</span><span class="nb">variable term is</span>
</div><div id="l326" class="code_block"><span class="nb">to be printed.  If either call succeeds, then it is assumed that the</span>
</div><div id="l327" class="code_block"><span class="nb">term has been output, else it is printed as usual.  If {</span><span class="nv">\tt</span><span class="nb"> bool} is</span>
</div><div id="l328" class="code_block"><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> false}, these predicates are not called. Default value is {</span><span class="nv">\tt</span>
</div><div id="l329" class="code_block"><span class="nb">false}.  This option is set by the toplevel when writting the final</span>
</div><div id="l330" class="code_block"><span class="nb">values of variables, and by the debugging package when writting the</span>
</div><div id="l331" class="code_block"><span class="nb">goals in the tracing messages.  Thus you can vary the forms of these</span>
</div><div id="l332" class="code_block"><span class="nb">messages if you wish.</span>
</div><div id="l333" class="code_block"><span class="nb">}</span>
</div><div id="l334" class="code_block"><span class="nv">\item</span><span class="nb"> {</span><span class="nv">\tt</span><span class="nb"> max</span><span class="nv">\_</span><span class="nb">depth</span><span class="o">(+</span><span class="nb">Depth</span><span class="o">)</span><span class="nb">}. {</span><span class="nv">\tt</span><span class="nb"> Depth} is a positive integer or</span>
</div><div id="l335" class="code_block"><span class="nb">zero. If positive, it denotes the depth limit on printing compound</span>
</div><div id="l336" class="code_block"><span class="nb">terms. If {</span><span class="nv">\tt</span><span class="nb"> Depth} is zero, there is no limit. Default value is</span>
</div><div id="l337" class="code_block"><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> </span><span class="m">0</span><span class="nb">} </span><span class="o">(</span><span class="nb">no limit</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l338" class="code_block"><span class="c">%</span>
</div><div id="l339" class="code_block"><span class="nv">\item</span><span class="nb"> {</span><span class="nv">\tt</span><span class="nb"> priority</span><span class="o">(+</span><span class="nb">Prio</span><span class="o">)</span><span class="nb">} {</span><span class="nv">\tt</span><span class="nb"> Prio} is an integer between </span><span class="m">1</span><span class="nb"> and</span>
</div><div id="l340" class="code_block"><span class="m">1200</span><span class="nb">.  If the term to be printed has higher priority than {</span><span class="nv">\tt</span><span class="nb"> Prio},</span>
</div><div id="l341" class="code_block"><span class="nb">it will be printed parenthesized.  Default value is </span><span class="m">1200</span><span class="nb"> </span><span class="o">(</span><span class="nb">no term</span>
</div><div id="l342" class="code_block"><span class="nb">parenthesized</span><span class="o">)</span><span class="nb">.</span>
</div><div id="l343" class="code_block"><span class="nv">\end</span><span class="nb">{itemize}</span>
</div><div id="l344" class="code_block">
</div><div id="l345" class="code_block"><span class="nb">From the following examples it can be seen that {</span><span class="nv">\tt</span>
</div><div id="l346" class="code_block"><span class="nb">write</span><span class="nv">\_</span><span class="nb">term</span><span class="o">/</span><span class="nv">\{</span><span class="m">2</span><span class="nb">,</span><span class="m">3</span><span class="nv">\}</span><span class="nb">} can duplicate the behavior of a number of other</span>
</div><div id="l347" class="code_block"><span class="nb">I</span><span class="o">/</span><span class="nb">O predicates such as {</span><span class="nv">\tt</span><span class="nb"> writeq</span><span class="o">/</span><span class="nv">\{</span><span class="m">1</span><span class="nb">,</span><span class="m">2</span><span class="nv">\}</span><span class="nb">}, {</span><span class="nv">\tt</span>
</div><div id="l348" class="code_block"><span class="nb">write</span><span class="nv">\_</span><span class="nb">canonical</span><span class="o">/</span><span class="nv">\{</span><span class="m">1</span><span class="nb">,</span><span class="m">2</span><span class="nv">\}</span><span class="nb">}, etc.</span>
</div><div id="l349" class="code_block"><span class="nb">{</span><span class="nv">\small</span>
</div><div id="l350" class="code_block"><span class="nv">\begin</span><span class="nb">{verbatim}</span>
</div><div id="l351" class="code_block">
</div><div id="l352" class="code_block"><span class="nb">| ?</span><span class="o">-</span><span class="nb"> write_term</span><span class="o">(</span><span class="nb">f</span><span class="o">(</span><span class="m">1</span><span class="o">+</span><span class="m">2</span><span class="nb">,&#39;A&#39;,&quot;string&quot;,&#39;</span><span class="s">$</span>VAR&#39;(3),&#39;<span class="s">$</span><span class="nb">VAR&#39;</span><span class="o">(</span><span class="nb">&#39;Temp&#39;</span><span class="o">)</span><span class="nb">,</span><span class="o">(</span><span class="nb">multifile foo</span><span class="o">))</span><span class="nb">,</span><span class="o">[])</span><span class="nb">.</span>
</div><div id="l353" class="code_block"><span class="nb">f</span><span class="o">(</span><span class="m">1</span><span class="nb"> </span><span class="o">+</span><span class="nb"> </span><span class="m">2</span><span class="nb">,A,&quot;string&quot;,</span><span class="s">$</span>VAR(3),<span class="s">$</span><span class="nb">VAR</span><span class="o">(</span><span class="nb">Temp</span><span class="o">)</span><span class="nb">,</span><span class="o">(</span><span class="nb">multifile foo</span><span class="o">))</span>
</div><div id="l354" class="code_block"><span class="nb">yes</span>
</div><div id="l355" class="code_block">
</div><div id="l356" class="code_block"><span class="nb">| ?</span><span class="o">-</span><span class="nb"> write_term</span><span class="o">(</span><span class="nb">f</span><span class="o">(</span><span class="m">1</span><span class="o">+</span><span class="m">2</span><span class="nb">,&#39;A&#39;,&quot;string&quot;,&#39;</span><span class="s">$</span>VAR&#39;(3),&#39;<span class="s">$</span><span class="nb">VAR&#39;</span><span class="o">(</span><span class="nb">&#39;Temp&#39;</span><span class="o">)</span><span class="nb">,</span><span class="o">(</span><span class="nb">multifile foo</span><span class="o">))</span><span class="nb">,</span>
</div><div id="l357" class="code_block"><span class="nb">                </span><span class="o">[</span><span class="nb">quoted</span><span class="o">(</span><span class="nb">true</span><span class="o">)])</span><span class="nb">.</span>
</div><div id="l358" class="code_block"><span class="nb">f</span><span class="o">(</span><span class="m">1</span><span class="nb"> </span><span class="o">+</span><span class="nb"> </span><span class="m">2</span><span class="nb">,&#39;A&#39;,&quot;string&quot;,&#39;</span><span class="s">$</span>VAR&#39;(3),&#39;<span class="s">$</span><span class="nb">VAR&#39;</span><span class="o">(</span><span class="nb">&#39;Temp&#39;</span><span class="o">)</span><span class="nb">,</span><span class="o">(</span><span class="nb">multifile foo</span><span class="o">))</span>
</div><div id="l359" class="code_block"><span class="nb">yes</span>
</div><div id="l360" class="code_block">
</div><div id="l361" class="code_block"><span class="nb">| ?</span><span class="o">-</span><span class="nb"> write_term</span><span class="o">(</span><span class="nb">f</span><span class="o">(</span><span class="m">1</span><span class="o">+</span><span class="m">2</span><span class="nb">,&#39;A&#39;,&quot;string&quot;,&#39;</span><span class="s">$</span>VAR&#39;(3),&#39;<span class="s">$</span><span class="nb">VAR&#39;</span><span class="o">(</span><span class="nb">&#39;Temp&#39;</span><span class="o">)</span><span class="nb">,</span><span class="o">(</span><span class="nb">multifile foo</span><span class="o">))</span><span class="nb">,</span>
</div><div id="l362" class="code_block"><span class="nb">                </span><span class="o">[</span><span class="nb">quoted</span><span class="o">(</span><span class="nb">true</span><span class="o">)</span><span class="nb">,ignore_ops</span><span class="o">(</span><span class="nb">true</span><span class="o">)</span><span class="nb">,numbervars</span><span class="o">(</span><span class="nb">true</span><span class="o">)])</span><span class="nb">.</span>
</div><div id="l363" class="code_block"><span class="nb">f</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">,&#39;A&#39;,&#39;.&#39;</span><span class="o">(</span><span class="m">115</span><span class="nb">,&#39;.&#39;</span><span class="o">(</span><span class="m">116</span><span class="nb">,&#39;.&#39;</span><span class="o">(</span><span class="m">114</span><span class="nb">,&#39;.&#39;</span><span class="o">(</span><span class="m">105</span><span class="nb">,&#39;.&#39;</span><span class="o">(</span><span class="m">110</span><span class="nb">,&#39;.&#39;</span><span class="o">(</span><span class="m">103</span><span class="nb">,</span><span class="o">[]))))))</span><span class="nb">,D,Temp,</span><span class="o">(</span><span class="nb">multifile foo</span><span class="o">))</span>
</div><div id="l364" class="code_block"><span class="nb">yes</span>
</div><div id="l365" class="code_block">
</div><div id="l366" class="code_block"><span class="nb">| ?</span><span class="o">-</span><span class="nb"> write_term</span><span class="o">(</span><span class="nb">f</span><span class="o">(</span><span class="m">1</span><span class="o">+</span><span class="m">2</span><span class="nb">,&#39;A&#39;,&quot;string&quot;,&#39;</span><span class="s">$</span>VAR&#39;(3),&#39;<span class="s">$</span><span class="nb">VAR&#39;</span><span class="o">(</span><span class="nb">&#39;Temp&#39;</span><span class="o">)</span><span class="nb">,</span><span class="o">(</span><span class="nb">multifile foo</span><span class="o">))</span><span class="nb">,</span>
</div><div id="l367" class="code_block"><span class="nb">                </span><span class="o">[</span><span class="nb">quoted</span><span class="o">(</span><span class="nb">true</span><span class="o">)</span><span class="nb">,ignore_ops</span><span class="o">(</span><span class="nb">true</span><span class="o">)</span><span class="nb">,numbervars</span><span class="o">(</span><span class="nb">true</span><span class="o">)</span><span class="nb">,priority</span><span class="o">(</span><span class="m">1000</span><span class="o">)])</span><span class="nb">.</span>
</div><div id="l368" class="code_block"><span class="nb">f</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">,&#39;A&#39;,&#39;.&#39;</span><span class="o">(</span><span class="m">115</span><span class="nb">,&#39;.&#39;</span><span class="o">(</span><span class="m">116</span><span class="nb">,&#39;.&#39;</span><span class="o">(</span><span class="m">114</span><span class="nb">,&#39;.&#39;</span><span class="o">(</span><span class="m">105</span><span class="nb">,&#39;.&#39;</span><span class="o">(</span><span class="m">110</span><span class="nb">,&#39;.&#39;</span><span class="o">(</span><span class="m">103</span><span class="nb">,</span><span class="o">[]))))))</span><span class="nb">,D,Temp,multifile</span><span class="o">(</span><span class="nb">foo</span><span class="o">))</span>
</div><div id="l369" class="code_block"><span class="nb">yes</span>
</div><div id="l370" class="code_block"><span class="nv">\end</span><span class="nb">{verbatim}</span>
</div><div id="l371" class="code_block"><span class="nb">}</span>
</div><div id="l372" class="code_block">
</div><div id="l373" class="code_block"><span class="nv">\ouritem</span><span class="nb">{writeln</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">\tt</span><span class="nb"> writeln</span><span class="o">/</span><span class="m">1</span><span class="nb">}}</span>
</div><div id="l374" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> writeln</span><span class="o">(</span><span class="nb">Term</span><span class="o">)</span><span class="nb">} can be defined as {</span><span class="nv">\tt</span><span class="nb"> write</span><span class="o">(</span><span class="nb">Term</span><span class="o">)</span><span class="nb">, nl}.</span>
</div><div id="l375" class="code_block">
</div><div id="l376" class="code_block"><span class="nv">\ouritem</span><span class="nb">{writeln</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">\tt</span><span class="nb"> writeln</span><span class="o">/</span><span class="m">2</span><span class="nb">}}</span>
</div><div id="l377" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> writeln</span><span class="o">(</span><span class="nb">Term</span><span class="o">)</span><span class="nb">} can be defined as {</span><span class="nv">\tt</span><span class="nb"> write</span><span class="o">(</span><span class="nb">Stream,Term</span><span class="o">)</span><span class="nb">,</span>
</div><div id="l378" class="code_block"><span class="nb">    nl</span><span class="o">(</span><span class="nb">Stream</span><span class="o">)</span><span class="nb">}.</span>
</div><div id="l379" class="code_block">
</div><div id="l380" class="code_block"><span class="nv">\ouritem</span><span class="nb">{display</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">\tt</span><span class="nb"> display</span><span class="o">/</span><span class="m">1</span><span class="nb">}}</span>
</div><div id="l381" class="code_block"><span class="nb">    The HiLog term {</span><span class="nv">\tt</span><span class="nb"> Term} is displayed on the terminal </span><span class="o">(</span><span class="nb">standard output </span>
</div><div id="l382" class="code_block"><span class="nb">    stream</span><span class="o">)</span><span class="nb">, according to the operator declarations in force. In other words,</span>
</div><div id="l383" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> display</span><span class="o">/</span><span class="m">1</span><span class="nb">} is similar to {</span><span class="nv">\tt</span><span class="nb"> write</span><span class="o">/</span><span class="m">1</span><span class="nb">} but the result is always</span>
</div><div id="l384" class="code_block"><span class="nb">    written on {</span><span class="nv">\tt</span><span class="nb"> ``userout&#39;&#39;}</span><span class="nv">\@</span><span class="nb">.  Like {</span><span class="nv">\tt</span><span class="nb"> write</span><span class="o">/</span><span class="m">1</span><span class="nb">}, {</span><span class="nv">\tt</span><span class="nb"> display</span><span class="o">/</span><span class="m">1</span><span class="nb">} </span>
</div><div id="l385" class="code_block"><span class="nb">    always succeeds without producing an error. After returning from a call </span>
</div><div id="l386" class="code_block"><span class="nb">    to this predicate, the current output stream remains unchanged.</span>
</div><div id="l387" class="code_block">
</div><div id="l388" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{write</span><span class="nv">\_</span><span class="nb">prolog</span><span class="o">(</span><span class="nb">?Term</span><span class="o">)</span><span class="nb">}{HiLog}</span><span class="nv">\index</span><span class="nb">{{</span><span class="nv">\tt</span><span class="nb"> write</span><span class="nv">\_</span><span class="nb">prolog</span><span class="o">/</span><span class="m">1</span><span class="nb">}}</span>
</div><div id="l389" class="code_block"><span class="nb">    This predicate acts as does {</span><span class="nv">\tt</span><span class="nb"> write</span><span class="o">/</span><span class="m">1</span><span class="nb">} except that</span>
</div><div id="l390" class="code_block"><span class="nb">    any HiLog term {</span><span class="nv">\tt</span><span class="nb"> Term} is written as a Prolog term. </span>
</div><div id="l391" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> write</span><span class="nv">\_</span><span class="nb">prolog</span><span class="o">/</span><span class="m">1</span><span class="nb">} outputs {</span><span class="nv">\tt</span><span class="nb"> Term} according to the operator </span>
</div><div id="l392" class="code_block"><span class="nb">    declarations</span>
</div><div id="l393" class="code_block"><span class="nb">    in force.  Because of this, it differs from {</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">1</span><span class="nb">} </span>
</div><div id="l394" class="code_block"><span class="nb">    described below, despite the fact that both predicates write HiLog terms</span>
</div><div id="l395" class="code_block"><span class="nb">    as Prolog terms.</span>
</div><div id="l396" class="code_block">
</div><div id="l397" class="code_block"><span class="nv">\ournewitem</span><span class="nb">{write</span><span class="nv">\_</span><span class="nb">prolog</span><span class="o">(+</span><span class="nb">Stream,?Term</span><span class="o">)</span><span class="nb">}{HiLog}</span><span class="nv">\index</span><span class="nb">{{</span><span class="nv">\tt</span><span class="nb"> write</span><span class="nv">\_</span><span class="nb">prolog</span><span class="o">/</span><span class="m">2</span><span class="nb">}}</span>
</div><div id="l398" class="code_block"><span class="nb">	{</span><span class="nv">\tt</span><span class="nb"> write</span><span class="nv">\_</span><span class="nb">prolog</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="l399" class="code_block"><span class="nb">	write</span><span class="nv">\_</span><span class="nb">prolog</span><span class="o">/</span><span class="m">1</span><span class="nb">} but the output stream is explicitly</span>
</div><div id="l400" class="code_block"><span class="nb">	designated using the first argument.</span>
</div><div id="l401" class="code_block">
</div><div id="l402" class="code_block"><span class="nv">\ouritem</span><span class="nb">{writeq</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">\tt</span><span class="nb"> writeq</span><span class="o">/</span><span class="m">1</span><span class="nb">}}</span>
</div><div id="l403" class="code_block"><span class="nb">    Acts as {</span><span class="nv">\tt</span><span class="nb"> write</span><span class="o">(</span><span class="nb">Term</span><span class="o">)</span><span class="nb">}, but atoms and functors are quoted</span>
</div><div id="l404" class="code_block"><span class="nb">    whenever necessary to make the result acceptable as input to </span>
</div><div id="l405" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> read</span><span class="o">/</span><span class="m">1</span><span class="nb">}</span><span class="nv">\@</span><span class="nb">. {</span><span class="nv">\tt</span><span class="nb"> writeq</span><span class="o">/</span><span class="m">1</span><span class="nb">} treats treats terms of the form </span>
</div><div id="l406" class="code_block"><span class="nb">    </span><span class="nv">\verb</span><span class="nb">|&#39;</span><span class="nv">\VAR</span><span class="nb">&#39;</span><span class="o">(</span><span class="nb">N</span><span class="o">)</span><span class="nb">| the same way as {</span><span class="nv">\tt</span><span class="nb"> write</span><span class="o">/</span><span class="m">1</span><span class="nb">}, writing {</span><span class="nv">\tt</span><span class="nb"> A} if</span>
</div><div id="l407" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> N}</span><span class="o">=</span><span class="nb"> </span><span class="m">0</span><span class="nb">, etc. </span>
</div><div id="l408" class="code_block"><span class="c">%% $</span>
</div><div id="l409" class="code_block">
</div><div id="l410" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> writeq</span><span class="o">/</span><span class="m">1</span><span class="nb">} always succeeds without producing an error.</span>
</div><div id="l411" class="code_block">
</div><div id="l412" class="code_block"><span class="nv">\ouritem</span><span class="nb">{writeq</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">\tt</span><span class="nb"> writeq</span><span class="o">/</span><span class="m">2</span><span class="nb">}}</span>
</div><div id="l413" class="code_block"><span class="nb">	{</span><span class="nv">\tt</span><span class="nb"> writeq</span><span class="o">/</span><span class="m">2</span><span class="nb">} has the same behavior as {</span><span class="nv">\tt</span><span class="nb"> writeq</span><span class="o">/</span><span class="m">1</span><span class="nb">} but the</span>
</div><div id="l414" class="code_block"><span class="nb">	output stream is explicitly designated using the first argument.</span>
</div><div id="l415" class="code_block">
</div><div id="l416" 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">?Term</span><span class="o">)</span><span class="nb">}</span><span class="nv">\index</span><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">1</span><span class="nb">}}</span>
</div><div id="l417" class="code_block"><span class="nb">    This predicate is provided so that the HiLog term {</span><span class="nv">\tt</span><span class="nb"> Term}, </span>
</div><div id="l418" class="code_block"><span class="nb">    if written to a file, can be read back using {</span><span class="nv">\tt</span><span class="nb"> read</span><span class="o">/</span><span class="m">1</span><span class="nb">} regardless of </span>
</div><div id="l419" class="code_block"><span class="nb">    special characters appearing in {</span><span class="nv">\tt</span><span class="nb"> Term} or prevailing operator </span>
</div><div id="l420" class="code_block"><span class="nb">    declarations. Like {</span><span class="nv">\tt</span><span class="nb"> write</span><span class="nv">\_</span><span class="nb">prolog</span><span class="o">/</span><span class="m">1</span><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">1</span><span class="nb">} </span>
</div><div id="l421" class="code_block"><span class="nb">    writes all proper HiLog terms to the current output stream using the </span>
</div><div id="l422" class="code_block"><span class="nb">    standard Prolog syntax </span><span class="o">(</span><span class="nb">see Section~</span><span class="nv">\ref</span><span class="nb">{TermSyntax} on the standard </span>
</div><div id="l423" class="code_block"><span class="nb">    syntax of HiLog terms</span><span class="o">)</span><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">1</span><span class="nb">} also quotes atoms and </span>
</div><div id="l424" class="code_block"><span class="nb">    functors as {</span><span class="nv">\tt</span><span class="nb"> writeq</span><span class="o">/</span><span class="m">1</span><span class="nb">} does, to make them acceptable as input of </span>
</div><div id="l425" class="code_block"><span class="nb">    {</span><span class="nv">\tt</span><span class="nb"> read</span><span class="o">/</span><span class="m">1</span><span class="nb">}</span><span class="nv">\@</span><span class="nb">.  Operator declarations are not taken into consideration,</span>
</div><div id="l426" class="code_block"><span class="nb">    and compound terms are therefore always written in the form:</span>
</div><div id="l427" class="code_block">
</div><div id="l428" class="code_block"><span class="nb">		</span><span class="nv">\[</span><span class="nb"> </span><span class="nv">\langle</span><span class="nb"> predicate</span><span class="nv">\</span><span class="nb"> name </span><span class="nv">\rangle</span>
</div><div id="l429" class="code_block"><span class="nb">			</span><span class="o">(</span><span class="nv">\langle</span><span class="nb"> arg_</span><span class="m">1</span><span class="nb"> </span><span class="nv">\rangle</span><span class="nb">, </span><span class="nv">\ldots</span><span class="nb">,</span>
</div><div id="l430" class="code_block"><span class="nb">			 </span><span class="nv">\langle</span><span class="nb"> arg_n </span><span class="nv">\rangle</span><span class="o">)</span><span class="nb"> </span><span class="nv">\]</span>
</div><div id="l431" class="code_block">
</div><div id="l432" class="code_block"><span class="nb">    Unlike {</span><span class="nv">\tt</span><span class="nb"> writeq</span><span class="o">/</span><span class="m">1</span><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">1</span><span class="nb">} does not treat terms </span>
</div><div id="l433" class="code_block"><span class="nb">    of the form </span><span class="nv">\verb</span><span class="nb">|&#39;</span><span class="s">$</span>VAR&#39;(N)| specially. It writes square bracket lists 
</div><div id="l434" class="code_block">    using <span class="nb">{</span><span class="k">\tt</span> &#39;.&#39;/2<span class="nb">}</span> and <span class="nb">{</span><span class="k">\tt</span> []<span class="nb">}</span> (that is, <span class="nb">{</span><span class="k">\tt</span> [foo, bar]<span class="nb">}</span> is written 
</div><div id="l435" class="code_block">    as <span class="k">\verb</span>|&#39;.&#39;(foo,&#39;.&#39;(bar,[]))|).
</div><div id="l436" class="code_block"><span class="c">%% $</span>
</div><div id="l437" class="code_block">
</div><div id="l438" class="code_block"><span class="k">\ournewitem</span><span class="nb">{</span>read<span class="k">\_canonical</span>(-Term)<span class="nb">}{</span>basics<span class="nb">}</span> <span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span>
</div><div id="l439" class="code_block">read<span class="k">\_canonical</span>/1<span class="nb">}}</span> 
</div><div id="l440" class="code_block">Reads a term that is in canonical format from the
</div><div id="l441" class="code_block">current input stream and returns it in <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span>. On end-of-file, it
</div><div id="l442" class="code_block">returns the atom <span class="nb">{</span><span class="k">\tt</span> end<span class="k">\_of\_file</span><span class="nb">}</span>.  If it encounters an error, it
</div><div id="l443" class="code_block">prints an error message on stderr and returns the atom <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l444" class="code_block">read<span class="k">\_canonical\_error</span><span class="nb">}</span>. This is significantly faster than <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l445" class="code_block">read/1<span class="nb">}</span>, but requires the input to be in canonical form.
</div><div id="l446" class="code_block">
</div><div id="l447" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>write<span class="k">\_canonical</span>(+Stream, ?Term)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> write<span class="k">\_canonical</span>/2<span class="nb">}}</span>
</div><div id="l448" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> write<span class="k">\_canonical</span>/2<span class="nb">}</span> has the same behavior as <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l449" class="code_block">	write<span class="k">\_canonical</span>/1<span class="nb">}</span> but the output stream is explicitly
</div><div id="l450" class="code_block">	designated using the first argument.
</div><div id="l451" class="code_block">
</div><div id="l452" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>print(?Term)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> print/1<span class="nb">}}</span>
</div><div id="l453" class="code_block">    This predicate is intended to provide a handle for user-defined 
</div><div id="l454" class="code_block">    pretty-printing.  Currently it is defined as <span class="nb">{</span><span class="k">\em</span> write/1<span class="nb">}</span>.
</div><div id="l455" class="code_block">
</div><div id="l456" class="code_block"><span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l457" class="code_block">
</div><div id="l458" class="code_block"><span class="k">\comment</span><span class="nb">{</span> TLS: Taken out because this appears to be superceded by
</div><div id="l459" class="code_block">documentation in Manual 2
</div><div id="l460" class="code_block">
</div><div id="l461" class="code_block"><span class="k">\section</span><span class="nb">{</span>Special I/O<span class="nb">}</span>
</div><div id="l462" class="code_block">
</div><div id="l463" class="code_block"><span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l464" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>fmt<span class="k">\_read</span>(+Format, types(+T1,+T2,...), args(-A1,-A2,...), -RetCode)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> fmt<span class="k">\_read</span>/4<span class="nb">}}</span> 
</div><div id="l465" class="code_block"> This predicate implements C-style formatted input. It reads the current
</div><div id="l466" class="code_block"> input according to the <span class="nb">{</span><span class="k">\tt</span> Format<span class="nb">}</span> string.  <span class="nb">{</span><span class="k">\tt</span> Format<span class="nb">}</span> has the
</div><div id="l467" class="code_block"> same syntax as the input format in C. The term <span class="nb">{</span><span class="k">\tt</span> types(...)<span class="nb">}</span> lists the
</div><div id="l468" class="code_block"> types of the arguments; they must match the types specified in <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l469" class="code_block"> Format<span class="nb">}</span>. Here, 1 means string, 2 means integer, and 3 means float.
</div><div id="l470" class="code_block"> The term <span class="nb">{</span><span class="k">\tt</span> args()<span class="nb">}</span> specifies the variables for the input. <span class="nb">{</span><span class="k">\tt</span> RetCode<span class="nb">}</span>
</div><div id="l471" class="code_block"> specifies the return code: 0 -- ok; -1 -- end of file.
</div><div id="l472" class="code_block">
</div><div id="l473" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>read<span class="k">\_line</span>(-Line, -Status)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> read<span class="k">\_line</span>/2<span class="nb">}}</span> 
</div><div id="l474" class="code_block"> Reads the next line from the current input and puts it in <span class="nb">{</span><span class="k">\tt</span> Line<span class="nb">}</span>.
</div><div id="l475" class="code_block"> If the line is larger than the available buffer, then <span class="nb">{</span><span class="k">\tt</span> Status<span class="nb">}</span> is 0.
</div><div id="l476" class="code_block"> If the line was read in full, up to and including the newline character,
</div><div id="l477" class="code_block"> then <span class="nb">{</span><span class="k">\tt</span> Status<span class="nb">}</span> is 1. 
</div><div id="l478" class="code_block">
</div><div id="l479" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>fmt<span class="k">\_write</span>(+Format, args(-A1,-A2,...))<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> fmt<span class="k">\_write</span>/2<span class="nb">}}</span> 
</div><div id="l480" class="code_block"> Similar to formatted write in C. The semantics of the arguments is the
</div><div id="l481" class="code_block"> same as for <span class="nb">{</span><span class="k">\tt</span> fmt<span class="k">\_read</span>/4<span class="nb">}</span>.
</div><div id="l482" class="code_block">
</div><div id="l483" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>fmt<span class="k">\_write\_string</span>(-String, +Format, args(-A1,-A2,...))<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> fmt<span class="k">\_write</span>/2<span class="nb">}}</span> 
</div><div id="l484" class="code_block"> Like <span class="nb">{</span><span class="k">\tt</span> fmt<span class="k">\_write</span>/2<span class="nb">}</span>, but the output string is placed in <span class="nb">{</span><span class="k">\tt</span> String<span class="nb">}</span>.
</div><div id="l485" class="code_block">
</div><div id="l486" class="code_block"><span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l487" class="code_block"><span class="nb">}</span>
</div><div id="l488" class="code_block"><span class="c">% tls \section{Arithmetic} \label{Arithmetic}</span>
</div><div id="l489" class="code_block">
</div><div id="l490" class="code_block"><span class="c">%--- Need a very cursory description of arithmetic operations. \\</span>
</div><div id="l491" class="code_block"><span class="c">%--- Descriptions and of how we handle floats. \\</span>
</div><div id="l492" class="code_block">
</div><div id="l493" class="code_block">
</div><div id="l494" class="code_block"><span class="k">\section</span><span class="nb">{</span>Convenience<span class="nb">}</span> <span class="k">\label</span><span class="nb">{</span>Convenience<span class="nb">}</span>
</div><div id="l495" class="code_block">These predicates are standard and often self-explanatory, so they are 
</div><div id="l496" class="code_block">described only briefly.
</div><div id="l497" class="code_block"><span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l498" class="code_block">
</div><div id="l499" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>true<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> true/0<span class="nb">}}</span> 
</div><div id="l500" class="code_block"><span class="c">%\predindex{true/0~(I)}</span>
</div><div id="l501" class="code_block">    Always succeeds.
</div><div id="l502" class="code_block">
</div><div id="l503" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>otherwise<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> otherwise/0<span class="nb">}}</span> 
</div><div id="l504" class="code_block"><span class="c">%\predindex{otherwise/0~(B)}</span>
</div><div id="l505" class="code_block">    Same as <span class="nb">{</span><span class="k">\tt</span> true/0<span class="nb">}</span>.
</div><div id="l506" class="code_block">
</div><div id="l507" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>fail<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> fail/0<span class="nb">}}</span>
</div><div id="l508" class="code_block"><span class="c">%\predindex{fail/0~(I)}</span>
</div><div id="l509" class="code_block">    Always fails.
</div><div id="l510" class="code_block">
</div><div id="l511" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>X = Y<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> =/2<span class="nb">}}</span> 
</div><div id="l512" class="code_block"><span class="c">%\predindex{=/2~(I)}</span>
</div><div id="l513" class="code_block">    Defined as if by the clause ``Z=Z&#39;&#39;, i.e.~<span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> and~<span class="nb">{</span><span class="k">\tt</span> Y<span class="nb">}</span> are unified.
</div><div id="l514" class="code_block">
</div><div id="l515" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>X <span class="s">$</span><span class="nv">\backslash</span><span class="s">$</span><span class="k">\,</span>= Y<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> <span class="s">$</span><span class="nv">\backslash</span><span class="s">$</span>=/2<span class="nb">}}</span>
</div><div id="l516" class="code_block"><span class="c">%\predindex{$\backslash$ =/2~$(I)}</span>
</div><div id="l517" class="code_block"><span class="c">%\index{not unifiable|see{$\backslash$=/2}}</span>
</div><div id="l518" class="code_block">    Succeeds if~<span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> and~<span class="nb">{</span><span class="k">\tt</span> Y<span class="nb">}</span> are not unifiable,
</div><div id="l519" class="code_block">    fails if~<span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> and~<span class="nb">{</span><span class="k">\tt</span> Y<span class="nb">}</span> are unifiable.
</div><div id="l520" class="code_block">    It is thus equivalent to <span class="nb">{</span><span class="k">\tt</span> <span class="s">$</span><span class="nv">\backslash</span><span class="s">$</span>+<span class="nb">}</span><span class="k">\/</span><span class="nb">{</span><span class="k">\tt</span> (X = Y)<span class="nb">}</span>.
</div><div id="l521" class="code_block">
</div><div id="l522" class="code_block"><span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l523" class="code_block">
</div><div id="l524" class="code_block">
</div><div id="l525" class="code_block"><span class="k">\section</span><span class="nb">{</span>Negation and Control<span class="nb">}</span><span class="k">\label</span><span class="nb">{</span>sec:control<span class="nb">}</span>
</div><div id="l526" class="code_block"><span class="k">\index</span><span class="nb">{</span>control<span class="nb">}</span>
</div><div id="l527" class="code_block">
</div><div id="l528" class="code_block"><span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l529" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span><span class="k">\cut</span><span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> &quot;!/0<span class="nb">}}</span>  <span class="k">\index</span><span class="nb">{</span>cut<span class="nb">}</span> 
</div><div id="l530" class="code_block">    Cut (discard) all choice points made since the parent goal
</div><div id="l531" class="code_block">    started execution.
</div><div id="l532" class="code_block">    Cuts across tabled predicates are not valid.  The compiler checks for
</div><div id="l533" class="code_block">    such cuts, although whether the scope of a cut includes a tabled 
</div><div id="l534" class="code_block">    predicate is undecidable in the presence of meta-predicates like
</div><div id="l535" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> call/1<span class="nb">}</span>.
</div><div id="l536" class="code_block">    Further discussion of conditions allowing cuts and of their actions 
</div><div id="l537" class="code_block">    can be found in Section~<span class="k">\ref</span><span class="nb">{</span>tabling<span class="nb">_</span>env<span class="nb">}</span>.
</div><div id="l538" class="code_block">
</div><div id="l539" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>fail<span class="k">\_if</span>(+P)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> fail<span class="k">\_if</span>/1<span class="nb">}}</span>
</div><div id="l540" class="code_block">    If the goal <span class="nb">{</span><span class="k">\tt</span> P<span class="nb">}</span> has a solution, fails, otherwise it succeeds.
</div><div id="l541" class="code_block">    Equivalently, it is true iff <span class="nb">{</span><span class="k">\tt</span> call(P)<span class="nb">}</span> 
</div><div id="l542" class="code_block">    (see Section~<span class="k">\ref</span><span class="nb">{</span>meta<span class="nb">_</span>predicates<span class="nb">}</span>) is false. Argument <span class="nb">{</span><span class="k">\tt</span> P<span class="nb">}</span> 
</div><div id="l543" class="code_block">    must be ground for sound negation as failure, although no runtime 
</div><div id="l544" class="code_block">    checks are made by the system.
</div><div id="l545" class="code_block">
</div><div id="l546" class="code_block">    The standard predicate <span class="nb">{</span><span class="k">\tt</span> fail<span class="k">\_if</span>/1<span class="nb">}</span> is compiled by the 
</div><div id="l547" class="code_block">    XSB compiler.
</div><div id="l548" class="code_block">
</div><div id="l549" class="code_block">    Exceptions:
</div><div id="l550" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l551" class="code_block">    <span class="k">\item</span><span class="na">[{\tt instantiation\_error}]</span>
</div><div id="l552" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> P<span class="nb">}</span> is not instantiated.
</div><div id="l553" class="code_block">    <span class="k">\item</span><span class="na">[{\tt type\_error}]</span>
</div><div id="l554" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> P<span class="nb">}</span> is not a callable term.
</div><div id="l555" class="code_block">    <span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l556" class="code_block">
</div><div id="l557" class="code_block">
</div><div id="l558" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span><span class="s">$</span><span class="nv">\backslash</span><span class="s">$</span>+ +P<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> <span class="s">$</span><span class="nv">\backslash</span><span class="s">$</span>+/1<span class="nb">}}</span>
</div><div id="l559" class="code_block">    Exactly the same as <span class="nb">{</span><span class="k">\tt</span> fail<span class="k">\_if</span>/1<span class="nb">}</span>.  Its existence is only 
</div><div id="l560" class="code_block">    for compatibility with other Prolog systems.
</div><div id="l561" class="code_block">
</div><div id="l562" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>not +P<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> not/1<span class="nb">}}</span> 
</div><div id="l563" class="code_block">    If the goal <span class="nb">{</span><span class="k">\tt</span> P<span class="nb">}</span> has a solution, fails, otherwise it succeeds.
</div><div id="l564" class="code_block">    It is defined by:
</div><div id="l565" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>center<span class="nb">}</span>
</div><div id="l566" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>minipage<span class="nb">}{</span>2.40in<span class="nb">}</span>
</div><div id="l567" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l568" class="code_block">	not(P) :- call(P), !, fail.
</div><div id="l569" class="code_block">	not(<span class="nb">_</span>).
</div><div id="l570" class="code_block">    <span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l571" class="code_block">    <span class="k">\end</span><span class="nb">{</span>minipage<span class="nb">}</span>
</div><div id="l572" class="code_block">    <span class="k">\end</span><span class="nb">{</span>center<span class="nb">}</span>
</div><div id="l573" class="code_block">
</div><div id="l574" class="code_block">    Argument <span class="nb">{</span><span class="k">\tt</span> P<span class="nb">}</span> must be ground for sound negation, although no 
</div><div id="l575" class="code_block">    runtime checks are made by the system.
</div><div id="l576" class="code_block">
</div><div id="l577" class="code_block">    Note that in contrast to the other two kinds of negation as failure
</div><div id="l578" class="code_block">    (<span class="k">\not\</span> and <span class="nb">{</span><span class="k">\tt</span> fail<span class="k">\_if</span>/1<span class="nb">}</span>), predicate <span class="nb">{</span><span class="k">\tt</span> not/1<span class="nb">}</span> is not compiled
</div><div id="l579" class="code_block">    by the compiler but the above definition is used.
</div><div id="l580" class="code_block">
</div><div id="l581" class="code_block">    Exceptions: The same as <span class="nb">{</span><span class="k">\tt</span> call/1<span class="nb">}</span> 
</div><div id="l582" class="code_block">		(see Section~<span class="k">\ref</span><span class="nb">{</span>meta<span class="nb">_</span>predicates<span class="nb">}</span>).
</div><div id="l583" class="code_block">
</div><div id="l584" class="code_block"><span class="k">\ournewitem</span><span class="nb">{</span>tnot(+P)<span class="nb">}{</span>Tabling<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> tnot/1<span class="nb">}}</span><span class="k">\label</span><span class="nb">{</span>tnot/1<span class="nb">}</span>
</div><div id="l585" class="code_block">    The semantics of <span class="nb">{</span><span class="k">\tt</span> tnot/1<span class="nb">}</span> allows for correct execution of
</div><div id="l586" class="code_block">    programs with according to the well-founded semantics.  <span class="nb">{</span><span class="k">\tt</span> P<span class="nb">}</span>
</div><div id="l587" class="code_block">    must be a tabled predicate, 
</div><div id="l588" class="code_block"><span class="c">% tls: need to provide an example.</span>
</div><div id="l589" class="code_block"><span class="c">%and the actions of {\tt tnot/1} are</span>
</div><div id="l590" class="code_block"><span class="c">%presented in Figure~\ref{fig:tnot}. </span>
</div><div id="l591" class="code_block"><span class="c">%</span>
</div><div id="l592" class="code_block"><span class="c">%\input{tnot} </span>
</div><div id="l593" class="code_block"><span class="c">%</span>
</div><div id="l594" class="code_block">    For a detailed description of the actions of tabled negation for
</div><div id="l595" class="code_block">    in XSB <span class="k">\version\</span> see~<span class="k">\cite</span><span class="nb">{</span>SaSw98, SaSW96<span class="nb">}</span>.
</div><div id="l596" class="code_block">    Chapter~<span class="k">\ref</span><span class="nb">{</span>chap:TablingOverview<span class="nb">}</span> contains further discussion of the
</div><div id="l597" class="code_block">    functionality of <span class="nb">{</span><span class="k">\tt</span> tnot/1<span class="nb">}</span>.
</div><div id="l598" class="code_block">
</div><div id="l599" class="code_block">    Exceptions:
</div><div id="l600" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l601" class="code_block">    <span class="k">\item</span><span class="na">[{\tt instantiation\_error}]</span>
</div><div id="l602" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> P<span class="nb">}</span> is not ground (floundering occurs).
</div><div id="l603" class="code_block">    <span class="k">\item</span><span class="na">[{\tt type\_error}]</span>
</div><div id="l604" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> P<span class="nb">}</span> is not a callable term.
</div><div id="l605" class="code_block">    <span class="k">\item</span><span class="na">[{\tt table\_error}]</span>
</div><div id="l606" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> P<span class="nb">}</span> is not a call to a tabled predicate.
</div><div id="l607" class="code_block">    <span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l608" class="code_block">
</div><div id="l609" class="code_block">
</div><div id="l610" class="code_block">    <span class="k">\ournewitem</span><span class="nb">{</span>sk<span class="k">\_not</span>(+P)<span class="nb">}{</span>Tabling<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> sk<span class="k">\_not</span>/1<span class="nb">}}</span> 
</div><div id="l611" class="code_block"><span class="c">%% </span>
</div><div id="l612" class="code_block">If <span class="nb">{</span><span class="k">\tt</span> +P<span class="nb">}</span> is a tabled predicate, <span class="nb">{</span><span class="k">\tt</span> sk<span class="k">\_not</span>/1<span class="nb">}</span> acts as <span class="nb">{</span><span class="k">\tt</span> tnot/1<span class="nb">}</span>
</div><div id="l613" class="code_block">    but permits variables in its subgoal argument.  This replaces the
</div><div id="l614" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> &#39;t not&#39;/1<span class="nb">}</span> predicate of earlier XSB versions whose
</div><div id="l615" class="code_block">    implementation and semantics were dubious. The semantics in the
</div><div id="l616" class="code_block">    case of unbound variables is as follows: 
</div><div id="l617" class="code_block"><span class="c">%% </span>
</div><div id="l618" class="code_block"><span class="k">\begin</span><span class="nb">{</span>quote<span class="nb">}</span> 
</div><div id="l619" class="code_block"><span class="k">\tt</span> ... :- ...,~sk<span class="k">\_not</span>(p(X)),~...  <span class="k">\end</span><span class="nb">{</span>quote<span class="nb">}</span> 
</div><div id="l620" class="code_block"><span class="c">%% </span>
</div><div id="l621" class="code_block">is equivalent to 
</div><div id="l622" class="code_block"><span class="c">%%</span>
</div><div id="l623" class="code_block"><span class="k">\begin</span><span class="nb">{</span>quote<span class="nb">}</span>
</div><div id="l624" class="code_block"> <span class="k">\tt</span> ... :- ..., tnot(pp),~...<span class="k">\\</span> pp :- p(X).
</div><div id="l625" class="code_block"><span class="k">\end</span><span class="nb">{</span>quote<span class="nb">}</span> 
</div><div id="l626" class="code_block"><span class="c">%% </span>
</div><div id="l627" class="code_block">where <span class="nb">{</span><span class="k">\tt</span> pp<span class="nb">}</span> is a new proposition. Thus, the unbound variable <span class="s">$</span><span class="nb">X</span><span class="s">$</span> is
</div><div id="l628" class="code_block">treated as <span class="s">$</span><span class="nv">\tt</span><span class="nb"> tnot</span><span class="o">(</span><span class="nv">\exists</span><span class="nb"> X </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="s">$</span>.
</div><div id="l629" class="code_block">
</div><div id="l630" class="code_block">If <span class="nb">{</span><span class="k">\tt</span> +P<span class="nb">}</span> is a non-tabled predicate ensures that <span class="nb">{</span><span class="k">\tt</span> +P<span class="nb">}</span> is ground
</div><div id="l631" class="code_block">and called via a tabled predicate so that <span class="nb">{</span><span class="k">\tt</span> sk<span class="k">\_not</span>/1<span class="nb">}</span> can be used
</div><div id="l632" class="code_block">with non-tabled predicates as well, regardless of whether <span class="nb">{</span><span class="k">\tt</span> +P<span class="nb">}</span> is
</div><div id="l633" class="code_block">ground or not.
</div><div id="l634" class="code_block">
</div><div id="l635" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>P -&gt; Q ; R<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> -&gt;/2<span class="nb">}}</span> 
</div><div id="l636" class="code_block">    Analogous to if <span class="nb">{</span><span class="k">\tt</span> P<span class="nb">}</span> then <span class="nb">{</span><span class="k">\tt</span> Q<span class="nb">}</span> else <span class="nb">{</span><span class="k">\tt</span> R<span class="nb">}</span>, i.e.<span class="k">\</span> defined as 
</div><div id="l637" class="code_block">    if by
</div><div id="l638" class="code_block">	<span class="k">\begin</span><span class="nb">{</span>center<span class="nb">}</span>
</div><div id="l639" class="code_block">	<span class="k">\begin</span><span class="nb">{</span>minipage<span class="nb">}{</span>2.10in<span class="nb">}</span>
</div><div id="l640" class="code_block">	<span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l641" class="code_block">	(P -&gt; Q ; R) :- P, !, Q.
</div><div id="l642" class="code_block">	(P -&gt; Q ; R) :- R.
</div><div id="l643" class="code_block">	<span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l644" class="code_block">	<span class="k">\end</span><span class="nb">{</span>minipage<span class="nb">}</span>
</div><div id="l645" class="code_block">	<span class="k">\end</span><span class="nb">{</span>center<span class="nb">}</span>
</div><div id="l646" class="code_block">
</div><div id="l647" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>P -&gt; Q<span class="nb">}</span> <span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> -&gt;/2<span class="nb">}}</span> 
</div><div id="l648" class="code_block">    When occurring other than as one of the alternatives of a disjunction,
</div><div id="l649" class="code_block">    is equivalent to:
</div><div id="l650" class="code_block">	<span class="k">\begin</span><span class="nb">{</span>center<span class="nb">}</span>
</div><div id="l651" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> P -&gt; Q ; fail.<span class="nb">}</span>
</div><div id="l652" class="code_block">	<span class="k">\end</span><span class="nb">{</span>center<span class="nb">}</span>
</div><div id="l653" class="code_block">
</div><div id="l654" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>repeat<span class="nb">}</span> <span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> repeat/2<span class="nb">}}</span> 
</div><div id="l655" class="code_block">    Generates an infinite sequence of choice points (in other words it 
</div><div id="l656" class="code_block">    provides a very convenient way of executing a loop). It is defined 
</div><div id="l657" class="code_block">    by the clauses:
</div><div id="l658" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>center<span class="nb">}</span>
</div><div id="l659" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>minipage<span class="nb">}{</span>1.5in<span class="nb">}</span>
</div><div id="l660" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l661" class="code_block">	repeat.
</div><div id="l662" class="code_block">	repeat :- repeat.
</div><div id="l663" class="code_block">    <span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l664" class="code_block">    <span class="k">\end</span><span class="nb">{</span>minipage<span class="nb">}</span>
</div><div id="l665" class="code_block">    <span class="k">\end</span><span class="nb">{</span>center<span class="nb">}</span>
</div><div id="l666" class="code_block">
</div><div id="l667" class="code_block"><span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l668" class="code_block">
</div><div id="l669" class="code_block">
</div><div id="l670" class="code_block"><span class="k">\section</span><span class="nb">{</span>Meta-Logical<span class="nb">}</span><span class="k">\label</span><span class="nb">{</span>MetaLogical<span class="nb">}</span>
</div><div id="l671" class="code_block">
</div><div id="l672" class="code_block">To facilitate manipulation of terms as objects in themselves,
</div><div id="l673" class="code_block">XSB provides a number meta-logical predicates.  These
</div><div id="l674" class="code_block">predicates include the standard meta-logical predicates of Prolog,
</div><div id="l675" class="code_block">along with their usual semantics.  In addition are provided predicates
</div><div id="l676" class="code_block">which provide special operations on HiLog terms.  For a full
</div><div id="l677" class="code_block">discussion of Prolog and HiLog terms see Section~<span class="k">\ref</span><span class="nb">{</span>TermSyntax<span class="nb">}</span>.
</div><div id="l678" class="code_block">
</div><div id="l679" class="code_block"><span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l680" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>var(?X)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> var/1<span class="nb">}}</span> 
</div><div id="l681" class="code_block">    Succeeds if <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> is currently uninstantiated (i.e.<span class="k">\</span> is still a 
</div><div id="l682" class="code_block">    variable); otherwise it fails.  
</div><div id="l683" class="code_block">
</div><div id="l684" class="code_block">    Term <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> is uninstantiated if it has not been bound to anything, 
</div><div id="l685" class="code_block">    except possibly another uninstantiated variable. Note in particular,
</div><div id="l686" class="code_block">    that the HiLog term X(Y,Z) is considered to be instantiated.  There 
</div><div id="l687" class="code_block">    is no distinction between a Prolog and a HiLog variable.
</div><div id="l688" class="code_block">
</div><div id="l689" class="code_block">    Examples:
</div><div id="l690" class="code_block">    <span class="nb">{</span><span class="k">\footnotesize</span>
</div><div id="l691" class="code_block">     <span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l692" class="code_block">                | ?- var(X).
</div><div id="l693" class="code_block">                yes
</div><div id="l694" class="code_block">                | ?- var([X]).
</div><div id="l695" class="code_block">                no
</div><div id="l696" class="code_block">                | ?- var(X(Y,Z)).
</div><div id="l697" class="code_block">                no
</div><div id="l698" class="code_block">                | ?- var((X)).
</div><div id="l699" class="code_block">                yes
</div><div id="l700" class="code_block">                | ?- var((X)(Y)).
</div><div id="l701" class="code_block">                no
</div><div id="l702" class="code_block">     <span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}}</span>
</div><div id="l703" class="code_block">
</div><div id="l704" class="code_block">
</div><div id="l705" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>nonvar(?X)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> nonvar/1<span class="nb">}}</span> 
</div><div id="l706" class="code_block">    Succeeds if <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> is currently instantiated to a non-variable term;
</div><div id="l707" class="code_block">    otherwise it fails. This has exactly the opposite behaviour of 
</div><div id="l708" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> var/1<span class="nb">}</span><span class="k">\@</span>.
</div><div id="l709" class="code_block">
</div><div id="l710" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>atom(?X)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> atom/1<span class="nb">}}</span> 
</div><div id="l711" class="code_block">    Succeeds only if the <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> is currently instantiated to an atom, that
</div><div id="l712" class="code_block">    is to a Prolog or HiLog non-numeric constant.
</div><div id="l713" class="code_block">
</div><div id="l714" class="code_block">    Examples:
</div><div id="l715" class="code_block">    <span class="nb">{</span><span class="k">\footnotesize</span>
</div><div id="l716" class="code_block">     <span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l717" class="code_block">                | ?- atom(HiLog).
</div><div id="l718" class="code_block">                no
</div><div id="l719" class="code_block">                | ?- atom(10).
</div><div id="l720" class="code_block">                no
</div><div id="l721" class="code_block">                | ?- atom(&#39;HiLog&#39;).
</div><div id="l722" class="code_block">                yes
</div><div id="l723" class="code_block">                | ?- atom(X(a,b)).
</div><div id="l724" class="code_block">                no
</div><div id="l725" class="code_block">                | ?- atom(h).
</div><div id="l726" class="code_block">                yes
</div><div id="l727" class="code_block">                | ?- atom(+).
</div><div id="l728" class="code_block">                yes
</div><div id="l729" class="code_block">                | ?- atom([]).
</div><div id="l730" class="code_block">                yes
</div><div id="l731" class="code_block">     <span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}}</span>
</div><div id="l732" class="code_block">
</div><div id="l733" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>integer(?X)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> integer/1<span class="nb">}}</span>
</div><div id="l734" class="code_block">    Succeeds if <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> is currently instantiated to an integer; 
</div><div id="l735" class="code_block">    otherwise it fails. 
</div><div id="l736" class="code_block">
</div><div id="l737" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>real(?X)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> real/1<span class="nb">}}</span> 
</div><div id="l738" class="code_block">    Succeeds if <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> is currently instantiated to a floating point number;
</div><div id="l739" class="code_block">    otherwise it fails. 
</div><div id="l740" class="code_block">
</div><div id="l741" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>float(?X)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> float/1<span class="nb">}}</span> 
</div><div id="l742" class="code_block">    Same as <span class="nb">{</span><span class="k">\tt</span> real/1<span class="nb">}</span>. Succeeds if <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> is currently instantiated 
</div><div id="l743" class="code_block">    to a floating point number; otherwise it fails.  This predicate is 
</div><div id="l744" class="code_block">    included for compatibility with earlier versions of SBProlog.
</div><div id="l745" class="code_block">	
</div><div id="l746" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>number(?X)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> number/1<span class="nb">}}</span> 
</div><div id="l747" class="code_block">    Succeeds if <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> is currently instantiated to either an integer or 
</div><div id="l748" class="code_block">    a floating point number (real); otherwise it fails.
</div><div id="l749" class="code_block">
</div><div id="l750" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>atomic(?X)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> atomic/1<span class="nb">}}</span> 
</div><div id="l751" class="code_block">    Succeeds if <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> is currently instantiated to an atom or a number;
</div><div id="l752" class="code_block">    otherwise it fails.
</div><div id="l753" class="code_block">
</div><div id="l754" class="code_block">    Examples:
</div><div id="l755" class="code_block">    <span class="nb">{</span><span class="k">\footnotesize</span>
</div><div id="l756" class="code_block">     <span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l757" class="code_block">                | ?- atomic(10).
</div><div id="l758" class="code_block">                yes
</div><div id="l759" class="code_block">                | ?- atomic(p).
</div><div id="l760" class="code_block">                yes
</div><div id="l761" class="code_block">                | ?- atomic(h).
</div><div id="l762" class="code_block">                yes
</div><div id="l763" class="code_block">                | ?- atomic(h(X)).
</div><div id="l764" class="code_block">                no
</div><div id="l765" class="code_block">                | ?- atomic(&quot;foo&quot;).
</div><div id="l766" class="code_block">                no
</div><div id="l767" class="code_block">                | ?- atomic(&#39;foo&#39;).
</div><div id="l768" class="code_block">                yes
</div><div id="l769" class="code_block">                | ?- atomic(X).
</div><div id="l770" class="code_block">                no
</div><div id="l771" class="code_block">                | ?- atomic(X((Y))).
</div><div id="l772" class="code_block">                no
</div><div id="l773" class="code_block">     <span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}}</span>
</div><div id="l774" class="code_block">
</div><div id="l775" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>compound(?X)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> compound/1<span class="nb">}}</span> 
</div><div id="l776" class="code_block">    Succeeds if <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> is currently instantiated to a compound term (with 
</div><div id="l777" class="code_block">    arity greater that zero), i.e.<span class="k">\</span> to a nonvariable term that is not atomic;
</div><div id="l778" class="code_block">    otherwise it fails.
</div><div id="l779" class="code_block">
</div><div id="l780" class="code_block">    Examples:
</div><div id="l781" class="code_block">    <span class="nb">{</span><span class="k">\footnotesize</span>
</div><div id="l782" class="code_block">     <span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l783" class="code_block">                | ?- compound(1).
</div><div id="l784" class="code_block">                no
</div><div id="l785" class="code_block">                | ?- compound(foo(1,2,3)).
</div><div id="l786" class="code_block">                yes
</div><div id="l787" class="code_block">                | ?- compound([foo, bar]).
</div><div id="l788" class="code_block">                yes
</div><div id="l789" class="code_block">                | ?- compound(&quot;foo&quot;).
</div><div id="l790" class="code_block">                yes
</div><div id="l791" class="code_block">                | ?- compound(&#39;foo&#39;).
</div><div id="l792" class="code_block">                no
</div><div id="l793" class="code_block">                | ?- compound(X(a,b)).
</div><div id="l794" class="code_block">                yes
</div><div id="l795" class="code_block">                | ?- compound((a,b)).
</div><div id="l796" class="code_block">                yes	
</div><div id="l797" class="code_block">     <span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}}</span>
</div><div id="l798" class="code_block">
</div><div id="l799" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>structure(?X)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> structure/1<span class="nb">}}</span> 
</div><div id="l800" class="code_block">    Same as <span class="nb">{</span><span class="k">\tt</span> compound/1<span class="nb">}</span><span class="k">\@</span>. Its existence is only for compatibility 
</div><div id="l801" class="code_block">    with SB-Prolog version 3.1.
</div><div id="l802" class="code_block">
</div><div id="l803" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>is<span class="k">\_list</span>(?X)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> is<span class="k">\_list</span>/1<span class="nb">}}</span>
</div><div id="l804" class="code_block">    Succeeds if <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> is a <span class="nb">{</span><span class="k">\em</span> proper list<span class="nb">}</span>. In other words if it is 
</div><div id="l805" class="code_block">    either the atom <span class="nb">{</span><span class="k">\tt</span> []<span class="nb">}</span> or <span class="nb">{</span><span class="k">\tt</span> [H|T]<span class="nb">}</span> where H is any Prolog or HiLog
</div><div id="l806" class="code_block">    term and T is a proper list; otherwise it fails.
</div><div id="l807" class="code_block">
</div><div id="l808" class="code_block">    Examples:
</div><div id="l809" class="code_block">    <span class="nb">{</span><span class="k">\footnotesize</span>
</div><div id="l810" class="code_block">     <span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l811" class="code_block">                | ?- is<span class="nb">_</span>list([p(a,b,c), h(a,b)]).
</div><div id="l812" class="code_block">                yes
</div><div id="l813" class="code_block">                | ?- is<span class="nb">_</span>list([<span class="nb">_</span>,<span class="nb">_</span>]).
</div><div id="l814" class="code_block">                yes
</div><div id="l815" class="code_block">                | ?- is<span class="nb">_</span>list([a,b|X]).
</div><div id="l816" class="code_block">                no
</div><div id="l817" class="code_block">                | ?- is<span class="nb">_</span>list([a|b]).
</div><div id="l818" class="code_block">                no
</div><div id="l819" class="code_block">     <span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}}</span>
</div><div id="l820" class="code_block">
</div><div id="l821" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>is<span class="k">\_charlist</span>(+X)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> is<span class="k">\_charlist</span>/1<span class="nb">}}</span>
</div><div id="l822" class="code_block">    Succeeds if <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> is a Prolog string, <span class="nb">{</span><span class="k">\it</span> i.e.<span class="nb">}</span>, a list of
</div><div id="l823" class="code_block">    characters.
</div><div id="l824" class="code_block">    Examples:
</div><div id="l825" class="code_block">    <span class="nb">{</span><span class="k">\footnotesize</span>
</div><div id="l826" class="code_block">     <span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l827" class="code_block">                | ?- is<span class="nb">_</span>charlist(&quot;abc&quot;).
</div><div id="l828" class="code_block">                yes
</div><div id="l829" class="code_block">                | ?- is<span class="nb">_</span>charlist(abc).
</div><div id="l830" class="code_block">                no
</div><div id="l831" class="code_block">     <span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}}</span>
</div><div id="l832" class="code_block">
</div><div id="l833" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>is<span class="k">\_charlist</span>(+X,-Size)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> is<span class="k">\_charlist</span>/2<span class="nb">}}</span>
</div><div id="l834" class="code_block">    Works as above, but also returns the length of that string in the second
</div><div id="l835" class="code_block">    argument, which must be a variable.
</div><div id="l836" class="code_block">
</div><div id="l837" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>is<span class="k">\_attv</span>(+Term)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> is<span class="k">\_attv</span>/1<span class="nb">}}</span>
</div><div id="l838" class="code_block">    Succeeds is <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> is an attributed variable, and fails otherwise.
</div><div id="l839" class="code_block">
</div><div id="l840" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>is<span class="k">\_most\_general\_term</span>(?X)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span>
</div><div id="l841" class="code_block">is<span class="k">\_most\_general\_term</span>/1<span class="nb">}}</span>
</div><div id="l842" class="code_block">    Succeeds if <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> is compound term with all distinct variables
</div><div id="l843" class="code_block">as arguments, or if <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> is an atom. (It fails if X is a cons node.)
</div><div id="l844" class="code_block">    <span class="nb">{</span><span class="k">\footnotesize</span>
</div><div id="l845" class="code_block">     <span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l846" class="code_block">                | ?- is<span class="nb">_</span>most<span class="nb">_</span>general<span class="nb">_</span>term(f(<span class="nb">_</span>,<span class="nb">_</span>,<span class="nb">_</span>,<span class="nb">_</span>)).
</div><div id="l847" class="code_block">                yes
</div><div id="l848" class="code_block">                | ?- is<span class="nb">_</span>most<span class="nb">_</span>general<span class="nb">_</span>term(abc).
</div><div id="l849" class="code_block">                yes
</div><div id="l850" class="code_block">                | ?- is<span class="nb">_</span>most<span class="nb">_</span>general<span class="nb">_</span>term(f(X,Y,Z,X)).
</div><div id="l851" class="code_block">                no
</div><div id="l852" class="code_block">                | ?- is<span class="nb">_</span>most<span class="nb">_</span>general<span class="nb">_</span>term(f(X,Y,Z,a)).
</div><div id="l853" class="code_block">                no
</div><div id="l854" class="code_block">                | ?- is<span class="nb">_</span>most<span class="nb">_</span>general<span class="nb">_</span>term([<span class="nb">_</span>|<span class="nb">_</span>]).
</div><div id="l855" class="code_block">                no
</div><div id="l856" class="code_block">     <span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}}</span>
</div><div id="l857" class="code_block">
</div><div id="l858" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>callable(?X)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> callable/1<span class="nb">}}</span>
</div><div id="l859" class="code_block">    Succeeds if <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> is currently instantiated to a term that standard
</div><div id="l860" class="code_block">    predicate <span class="nb">{</span><span class="k">\tt</span> call/1<span class="nb">}</span> could take as an argument and not give an 
</div><div id="l861" class="code_block">    instantiation or type error.  Note that it only checks for errors of
</div><div id="l862" class="code_block">    predicate <span class="nb">{</span><span class="k">\tt</span> call/1<span class="nb">}</span>.  In other words it succeeds if <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span>
</div><div id="l863" class="code_block">    is an atom or a compound term; otherwise it fails.  Predicate
</div><div id="l864" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> callable/1<span class="nb">}</span> has no associated error conditions.
</div><div id="l865" class="code_block">
</div><div id="l866" class="code_block">    Examples:
</div><div id="l867" class="code_block">    <span class="nb">{</span><span class="k">\footnotesize</span>
</div><div id="l868" class="code_block">     <span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l869" class="code_block">                | ?- callable(p).
</div><div id="l870" class="code_block">                yes
</div><div id="l871" class="code_block">                | ?- callable(p(1,2,3)).
</div><div id="l872" class="code_block">                yes
</div><div id="l873" class="code_block">                | ?- callable([<span class="nb">_</span>,<span class="nb">_</span>]).
</div><div id="l874" class="code_block">                yes
</div><div id="l875" class="code_block">                | ?- callable(<span class="nb">_</span>(a)).
</div><div id="l876" class="code_block">                yes
</div><div id="l877" class="code_block">                | ?- callable(3.14).
</div><div id="l878" class="code_block">                no
</div><div id="l879" class="code_block">     <span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}}</span>
</div><div id="l880" class="code_block">
</div><div id="l881" class="code_block"><span class="k">\ournewitem</span><span class="nb">{</span>proper<span class="k">\_hilog</span>(?X)<span class="nb">}{</span>HiLog<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> proper<span class="k">\_hilog</span>/1<span class="nb">}}</span>
</div><div id="l882" class="code_block">    Succeeds if <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> is a proper HiLog term; otherwise it fails.
</div><div id="l883" class="code_block">
</div><div id="l884" class="code_block">    Examples:
</div><div id="l885" class="code_block">    (In this example and the rest of the examples of this section we assume
</div><div id="l886" class="code_block">     that <span class="nb">{</span><span class="k">\tt</span> h<span class="nb">}</span> is the only parameter symbol that has been declared a HiLog
</div><div id="l887" class="code_block">     symbol).
</div><div id="l888" class="code_block">
</div><div id="l889" class="code_block">    <span class="nb">{</span><span class="k">\footnotesize</span>
</div><div id="l890" class="code_block">     <span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l891" class="code_block">                | ?- proper<span class="nb">_</span>hilog(X).
</div><div id="l892" class="code_block">                no
</div><div id="l893" class="code_block">                | ?- proper<span class="nb">_</span>hilog(foo(a,f(b),[A])).
</div><div id="l894" class="code_block">                no
</div><div id="l895" class="code_block">                | ?- proper<span class="nb">_</span>hilog(X(a,b,c)).
</div><div id="l896" class="code_block">                yes
</div><div id="l897" class="code_block">                | ?- proper<span class="nb">_</span>hilog(3.6(2,4)).
</div><div id="l898" class="code_block">                yes
</div><div id="l899" class="code_block">                | ?- proper<span class="nb">_</span>hilog(h).
</div><div id="l900" class="code_block">                no
</div><div id="l901" class="code_block">                | ?- proper<span class="nb">_</span>hilog([a, [d, e, X(a)], c]).
</div><div id="l902" class="code_block">                yes
</div><div id="l903" class="code_block">                | ?- proper<span class="nb">_</span>hilog(a(a(X(a)))).
</div><div id="l904" class="code_block">                yes
</div><div id="l905" class="code_block">     <span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}}</span>
</div><div id="l906" class="code_block">
</div><div id="l907" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>functor(?Term, ?Functor, ?Arity)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> functor/3<span class="nb">}}</span>
</div><div id="l908" class="code_block">    Succeeds if the <span class="nb">{</span><span class="k">\em</span> functor<span class="nb">}</span> of the Prolog term <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> is 
</div><div id="l909" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> Functor<span class="nb">}</span> and the <span class="nb">{</span><span class="k">\em</span> arity<span class="nb">}</span> (number of arguments) of <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> is
</div><div id="l910" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> Arity<span class="nb">}</span><span class="k">\@</span>.  <span class="nb">{</span><span class="k">\tt</span> Functor<span class="nb">}</span> can be used in either the following two 
</div><div id="l911" class="code_block">    ways:
</div><div id="l912" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>enumerate<span class="nb">}</span>
</div><div id="l913" class="code_block">    <span class="k">\item</span> If <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> is initially instantiated, then
</div><div id="l914" class="code_block">          <span class="k">\begin</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l915" class="code_block">          <span class="k">\item</span> If <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> is a compound term, <span class="nb">{</span><span class="k">\tt</span> Functor<span class="nb">}</span> and 
</div><div id="l916" class="code_block">                <span class="nb">{</span><span class="k">\tt</span> Arity<span class="nb">}</span> are unified with the name and arity of 
</div><div id="l917" class="code_block">                its principal functor, respectively. 
</div><div id="l918" class="code_block">          <span class="k">\item</span> If <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> is an atom or a number, <span class="nb">{</span><span class="k">\tt</span> Functor<span class="nb">}</span> is 
</div><div id="l919" class="code_block">                unified with <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span>, and <span class="nb">{</span><span class="k">\tt</span> Arity<span class="nb">}</span> is unified with 0.
</div><div id="l920" class="code_block">          <span class="k">\end</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l921" class="code_block">    <span class="k">\item</span> If <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> is initially uninstantiated, then either both 
</div><div id="l922" class="code_block">          <span class="nb">{</span><span class="k">\tt</span> Functor<span class="nb">}</span> and <span class="nb">{</span><span class="k">\tt</span> Arity<span class="nb">}</span> must be instantiated, or <span class="nb">{</span><span class="k">\tt</span> Functor<span class="nb">}</span>
</div><div id="l923" class="code_block">          is instantiated to a number, and
</div><div id="l924" class="code_block">          <span class="k">\begin</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l925" class="code_block">          <span class="k">\item</span> If <span class="nb">{</span><span class="k">\tt</span> Arity<span class="nb">}</span> is an integer in the range 1..255, then
</div><div id="l926" class="code_block">                <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> becomes instantiated to <span class="nb">{</span><span class="k">\em</span> the most general 
</div><div id="l927" class="code_block">                Prolog term<span class="nb">}</span> having the specified <span class="nb">{</span><span class="k">\tt</span> Functor<span class="nb">}</span> and 
</div><div id="l928" class="code_block">                <span class="nb">{</span><span class="k">\tt</span> Arity<span class="nb">}</span> as principal functor and number of arguments,
</div><div id="l929" class="code_block">                respectively. The variables appearing as arguments of 
</div><div id="l930" class="code_block">                <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> are all distinct.
</div><div id="l931" class="code_block">          <span class="k">\item</span> If <span class="nb">{</span><span class="k">\tt</span> Arity<span class="nb">}</span> is 0, then <span class="nb">{</span><span class="k">\tt</span> Functor<span class="nb">}</span> must be either an 
</div><div id="l932" class="code_block">                atom or a number and it is unified with <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span>. 
</div><div id="l933" class="code_block">          <span class="k">\item</span> If <span class="nb">{</span><span class="k">\tt</span> Arity<span class="nb">}</span> is anything else, then <span class="nb">{</span><span class="k">\tt</span> functor/3<span class="nb">}</span> aborts.
</div><div id="l934" class="code_block">          <span class="k">\end</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l935" class="code_block">    <span class="k">\end</span><span class="nb">{</span>enumerate<span class="nb">}</span>
</div><div id="l936" class="code_block">
</div><div id="l937" class="code_block">    Exceptions:
</div><div id="l938" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l939" class="code_block">    <span class="k">\item</span><span class="na">[{\tt domain\_error}]</span>
</div><div id="l940" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> Functor<span class="nb">}</span> is instantiated to a compound term.
</div><div id="l941" class="code_block">    <span class="k">\item</span><span class="na">[{\tt instantiation\_error}]</span>
</div><div id="l942" class="code_block">	Both <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span>, and either <span class="nb">{</span><span class="k">\tt</span> Functor<span class="nb">}</span>, or <span class="nb">{</span><span class="k">\tt</span> Arity<span class="nb">}</span> are 
</div><div id="l943" class="code_block">	uninstantiated.
</div><div id="l944" class="code_block">    <span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l945" class="code_block">
</div><div id="l946" class="code_block">    Examples:
</div><div id="l947" class="code_block">    <span class="nb">{</span><span class="k">\footnotesize</span>
</div><div id="l948" class="code_block">     <span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l949" class="code_block">                | ?- functor(p(f(a),b,t), F, A).
</div><div id="l950" class="code_block">                F = p
</div><div id="l951" class="code_block">                A = 3
</div><div id="l952" class="code_block">
</div><div id="l953" class="code_block">                | ?- functor(T, foo, 3).
</div><div id="l954" class="code_block">                T = foo(<span class="nb">_</span>595708,<span class="nb">_</span>595712,<span class="nb">_</span>595716)
</div><div id="l955" class="code_block">
</div><div id="l956" class="code_block">                | ?- functor(T, 1.3, A).
</div><div id="l957" class="code_block">                T = 1.3
</div><div id="l958" class="code_block">                A = 0
</div><div id="l959" class="code_block">
</div><div id="l960" class="code_block">                | ?- functor(foo, F, 0).
</div><div id="l961" class="code_block">                F = foo
</div><div id="l962" class="code_block">
</div><div id="l963" class="code_block">                | ?- functor(&quot;foo&quot;, F, A).
</div><div id="l964" class="code_block">                F = .
</div><div id="l965" class="code_block">                A = 2
</div><div id="l966" class="code_block">
</div><div id="l967" class="code_block">                | ?- functor([], [], A).
</div><div id="l968" class="code_block">                A = 0
</div><div id="l969" class="code_block">
</div><div id="l970" class="code_block">                | ?- functor([2,3,4], F, A).
</div><div id="l971" class="code_block">                F = .
</div><div id="l972" class="code_block">                A = 2
</div><div id="l973" class="code_block">
</div><div id="l974" class="code_block">                | ?- functor(a+b, F, A).
</div><div id="l975" class="code_block">                F = +
</div><div id="l976" class="code_block">                A = 2
</div><div id="l977" class="code_block">
</div><div id="l978" class="code_block">                | ?- functor(f(a,b,c), F, A).
</div><div id="l979" class="code_block">                F = f
</div><div id="l980" class="code_block">                A = 3
</div><div id="l981" class="code_block">
</div><div id="l982" class="code_block">                | ?- functor(X(a,b,c), F, A).
</div><div id="l983" class="code_block">                F = apply
</div><div id="l984" class="code_block">                A = 4
</div><div id="l985" class="code_block">
</div><div id="l986" class="code_block">                | ?- functor(map(P)(a,b), F, A).
</div><div id="l987" class="code_block">                F = apply
</div><div id="l988" class="code_block">                A = 3
</div><div id="l989" class="code_block">
</div><div id="l990" class="code_block">                | ?- functor(T, foo(a), 1).
</div><div id="l991" class="code_block">                ++Error: Wrong type in argument 2 of functor/3
</div><div id="l992" class="code_block">                Aborting...
</div><div id="l993" class="code_block">
</div><div id="l994" class="code_block">                | ?- functor(T, F, 3).
</div><div id="l995" class="code_block">                ++Error: Uninstantiated argument 2 of functor/3
</div><div id="l996" class="code_block">                Aborting...
</div><div id="l997" class="code_block">
</div><div id="l998" class="code_block">                | ?- functor(T, foo, A).
</div><div id="l999" class="code_block">                ++Error: Uninstantiated argument 3 of functor/3
</div><div id="l1000" class="code_block">                Aborting...
</div><div id="l1001" class="code_block">     <span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}}</span>
</div><div id="l1002" class="code_block">
</div><div id="l1003" class="code_block"><span class="k">\ournewitem</span><span class="nb">{</span>hilog<span class="k">\_functor</span>(?Term, ?F, ?Arity)<span class="nb">}{</span>HiLog<span class="nb">}</span>
</div><div id="l1004" class="code_block"><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> hilog<span class="k">\_functor</span>/3<span class="nb">}}</span>
</div><div id="l1005" class="code_block">    The XSB standard predicate <span class="nb">{</span><span class="k">\tt</span> hilog<span class="k">\_functor</span>/3<span class="nb">}</span> succeeds 
</div><div id="l1006" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l1007" class="code_block">    <span class="k">\item</span> when <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> is a Prolog term and the principal function 
</div><div id="l1008" class="code_block">          symbol (<span class="nb">{</span><span class="k">\em</span> functor<span class="nb">}</span>) of <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> is <span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> and the
</div><div id="l1009" class="code_block">          <span class="nb">{</span><span class="k">\em</span> arity<span class="nb">}</span> (number of arguments) of <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> is 
</div><div id="l1010" class="code_block">          <span class="nb">{</span><span class="k">\tt</span> Arity<span class="nb">}</span>, or
</div><div id="l1011" class="code_block">    <span class="k">\item</span> when <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> is a HiLog term, having <span class="nb">{</span><span class="k">\em</span> name<span class="nb">}</span> <span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> 
</div><div id="l1012" class="code_block">          and the number of arguments <span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> is applied to, in the 
</div><div id="l1013" class="code_block">          HiLog term, is <span class="nb">{</span><span class="k">\tt</span> Arity<span class="nb">}</span>.
</div><div id="l1014" class="code_block">    <span class="k">\end</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l1015" class="code_block">    The first of these cases corresponds to the ``usual&#39;&#39; behaviour of
</div><div id="l1016" class="code_block">    Prolog&#39;s <span class="nb">{</span><span class="k">\tt</span> functor/3<span class="nb">}</span>, while the second is the extension of
</div><div id="l1017" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> functor/3<span class="nb">}</span> to handle HiLog terms. Like the Prolog&#39;s <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1018" class="code_block">    functor/3<span class="nb">}</span> predicate, <span class="nb">{</span><span class="k">\tt</span> hilog<span class="k">\_functor</span>/3<span class="nb">}</span> can be used in either
</div><div id="l1019" class="code_block">    of the following two ways:
</div><div id="l1020" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>enumerate<span class="nb">}</span>
</div><div id="l1021" class="code_block">    <span class="k">\item</span> If <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> is initially instantiated, then
</div><div id="l1022" class="code_block">          <span class="k">\begin</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l1023" class="code_block">          <span class="k">\item</span> If <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> is a Prolog compound term, <span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> and 
</div><div id="l1024" class="code_block">                <span class="nb">{</span><span class="k">\tt</span> Arity<span class="nb">}</span> are unified with the name and arity of 
</div><div id="l1025" class="code_block">                its principal functor, respectively.
</div><div id="l1026" class="code_block">          <span class="k">\item</span> If <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> is an atom or a number, <span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> is unified 
</div><div id="l1027" class="code_block">                with <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span>, and <span class="nb">{</span><span class="k">\tt</span> Arity<span class="nb">}</span> is unified with 0.
</div><div id="l1028" class="code_block">          <span class="k">\item</span> If <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> is any other HiLog term, <span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> and <span class="nb">{</span><span class="k">\tt</span> Arity<span class="nb">}</span> 
</div><div id="l1029" class="code_block">                are unified with the name and the number of arguments 
</div><div id="l1030" class="code_block">                that <span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> is applied to. Note that in this case <span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span>
</div><div id="l1031" class="code_block">                may still be uninstantiated.
</div><div id="l1032" class="code_block">          <span class="k">\end</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l1033" class="code_block">    <span class="k">\item</span> If <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> is initially uninstantiated, then at least
</div><div id="l1034" class="code_block">          <span class="nb">{</span><span class="k">\tt</span> Arity<span class="nb">}</span> must be instantiated, and
</div><div id="l1035" class="code_block">          <span class="k">\begin</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l1036" class="code_block">          <span class="k">\item</span> If <span class="nb">{</span><span class="k">\tt</span> Arity<span class="nb">}</span> is an integer in the range 1..255, then
</div><div id="l1037" class="code_block">                <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> becomes instantiated to <span class="nb">{</span><span class="k">\em</span> the most general 
</div><div id="l1038" class="code_block">                Prolog or HiLog term<span class="nb">}</span> having the specified <span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> and 
</div><div id="l1039" class="code_block">                <span class="nb">{</span><span class="k">\tt</span> Arity<span class="nb">}</span> as name and number of arguments <span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> is 
</div><div id="l1040" class="code_block">                applied to, respectively. The variables appearing as 
</div><div id="l1041" class="code_block">                arguments are all unique.
</div><div id="l1042" class="code_block">          <span class="k">\item</span> If <span class="nb">{</span><span class="k">\tt</span> Arity<span class="nb">}</span> is 0, then <span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> must be a Prolog or
</div><div id="l1043" class="code_block">                HiLog constant, and it is unified with <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span><span class="k">\@</span>. Note
</div><div id="l1044" class="code_block">                that in this case <span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> cannot be a compound term.
</div><div id="l1045" class="code_block">          <span class="k">\item</span> If <span class="nb">{</span><span class="k">\tt</span> Arity<span class="nb">}</span> is anything else, then <span class="nb">{</span><span class="k">\tt</span> hilog<span class="k">\_functor</span>/3<span class="nb">}</span>
</div><div id="l1046" class="code_block">                aborts.
</div><div id="l1047" class="code_block">          <span class="k">\end</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l1048" class="code_block">    <span class="k">\end</span><span class="nb">{</span>enumerate<span class="nb">}</span>
</div><div id="l1049" class="code_block">    In other words, the standard predicate <span class="nb">{</span><span class="k">\tt</span> hilog<span class="k">\_functor</span>/3<span class="nb">}</span> either
</div><div id="l1050" class="code_block">    decomposes a given HiLog term into its <span class="nb">{</span><span class="k">\em</span> name<span class="nb">}</span> and <span class="nb">{</span><span class="k">\em</span> arity<span class="nb">}</span>, or
</div><div id="l1051" class="code_block">    given an arity ---and possibly a name--- constructs the corresponding 
</div><div id="l1052" class="code_block">    HiLog term creating new uninstantiated variables for its arguments. 
</div><div id="l1053" class="code_block">    As happens with <span class="nb">{</span><span class="k">\tt</span> functor/3<span class="nb">}</span> all constants can be their own 
</div><div id="l1054" class="code_block">    principal function symbols.
</div><div id="l1055" class="code_block">
</div><div id="l1056" class="code_block">    Examples:
</div><div id="l1057" class="code_block">    <span class="nb">{</span><span class="k">\footnotesize</span>
</div><div id="l1058" class="code_block">     <span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1059" class="code_block">               | ?- hilog<span class="nb">_</span>functor(f(a,b,c), F, A).
</div><div id="l1060" class="code_block">               F = f
</div><div id="l1061" class="code_block">               A = 3
</div><div id="l1062" class="code_block">
</div><div id="l1063" class="code_block">               | ?- hilog<span class="nb">_</span>functor(X(a,b,c), F, A).
</div><div id="l1064" class="code_block">               X = <span class="nb">_</span>595836
</div><div id="l1065" class="code_block">               F = <span class="nb">_</span>595836
</div><div id="l1066" class="code_block">               A = 3
</div><div id="l1067" class="code_block">
</div><div id="l1068" class="code_block">               | ?- hilog<span class="nb">_</span>functor(map(P)(a,b), F, A).
</div><div id="l1069" class="code_block">               P = <span class="nb">_</span>595828
</div><div id="l1070" class="code_block">               F = map(<span class="nb">_</span>595828)
</div><div id="l1071" class="code_block">               A = 2
</div><div id="l1072" class="code_block">
</div><div id="l1073" class="code_block">               | ?- hilog<span class="nb">_</span>functor(T, p, 2).
</div><div id="l1074" class="code_block">               T = p(<span class="nb">_</span>595708,<span class="nb">_</span>595712)
</div><div id="l1075" class="code_block">
</div><div id="l1076" class="code_block">               | ?- hilog<span class="nb">_</span>functor(T, h, 2).
</div><div id="l1077" class="code_block">               T = apply(h,<span class="nb">_</span>595712,<span class="nb">_</span>595716)
</div><div id="l1078" class="code_block">
</div><div id="l1079" class="code_block">               | ?- hilog<span class="nb">_</span>functor(T, X, 3).
</div><div id="l1080" class="code_block">               T = apply(<span class="nb">_</span>595592,<span class="nb">_</span>595736,<span class="nb">_</span>595740,<span class="nb">_</span>595744)
</div><div id="l1081" class="code_block">               X = <span class="nb">_</span>595592
</div><div id="l1082" class="code_block">
</div><div id="l1083" class="code_block">               | ?- hilog<span class="nb">_</span>functor(T, p(f(a)), 2).
</div><div id="l1084" class="code_block">               T = apply(p(f(a)),<span class="nb">_</span>595792,<span class="nb">_</span>595796)
</div><div id="l1085" class="code_block">
</div><div id="l1086" class="code_block">               | ?- hilog<span class="nb">_</span>functor(T, h(p(a))(L1,L2), 1).
</div><div id="l1087" class="code_block">               T = apply(apply(apply(h,p(a)),<span class="nb">_</span>595984,<span class="nb">_</span>595776),<span class="nb">_</span>596128)
</div><div id="l1088" class="code_block">               L1 = <span class="nb">_</span>595984
</div><div id="l1089" class="code_block">               L2 = <span class="nb">_</span>595776
</div><div id="l1090" class="code_block">
</div><div id="l1091" class="code_block">               | ?- hilog<span class="nb">_</span>functor(T, a+b, 3).
</div><div id="l1092" class="code_block">               T = apply(a+b,<span class="nb">_</span>595820,<span class="nb">_</span>595824,<span class="nb">_</span>595828)
</div><div id="l1093" class="code_block">     <span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}}</span>
</div><div id="l1094" class="code_block">
</div><div id="l1095" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>arg(+Index, +Term, ?Argument)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> arg/3<span class="nb">}}</span>
</div><div id="l1096" class="code_block">    Unifies <span class="nb">{</span><span class="k">\tt</span> Argument<span class="nb">}</span> with the <span class="s">$</span><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> Index}^{th}</span><span class="s">$</span> argument of 
</div><div id="l1097" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span><span class="k">\@</span>, where the index is taken to start at <span class="s">$</span><span class="m">1</span><span class="s">$</span>.
</div><div id="l1098" class="code_block">    Initially, <span class="nb">{</span><span class="k">\tt</span> Index<span class="nb">}</span> must be instantiated to any integer and <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> 
</div><div id="l1099" class="code_block">    to any non-variable Prolog or HiLog term.
</div><div id="l1100" class="code_block">    The arguments of the <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> are numbered from~1 upwards. An atomic term
</div><div id="l1101" class="code_block">    has <span class="s">$</span><span class="m">0</span><span class="s">$</span> arguments. If the initial conditions are not satisfied or~<span class="s">$</span><span class="nb">I</span><span class="s">$</span> is 
</div><div id="l1102" class="code_block">    out of range, the call quietly fails.
</div><div id="l1103" class="code_block">
</div><div id="l1104" class="code_block">    Examples:
</div><div id="l1105" class="code_block">    <span class="nb">{</span><span class="k">\footnotesize</span>
</div><div id="l1106" class="code_block">     <span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1107" class="code_block">                   | ?- arg(2, p(a,b), A).
</div><div id="l1108" class="code_block">                   A = b
</div><div id="l1109" class="code_block">
</div><div id="l1110" class="code_block">                   | ?- arg(2, h(a,b), A).
</div><div id="l1111" class="code_block">                   A = a
</div><div id="l1112" class="code_block">
</div><div id="l1113" class="code_block">                   | ?- arg(0, foo, A).
</div><div id="l1114" class="code_block">                   no
</div><div id="l1115" class="code_block">
</div><div id="l1116" class="code_block">                   | ?- arg(2, [a,b,c], A).
</div><div id="l1117" class="code_block">                   A = [b,c]
</div><div id="l1118" class="code_block">
</div><div id="l1119" class="code_block">                   | ?- arg(2, &quot;HiLog&quot;, A).
</div><div id="l1120" class="code_block">                   A = [105,108,111,103]
</div><div id="l1121" class="code_block">
</div><div id="l1122" class="code_block">                   | ?- arg(2, a+b+c, A).
</div><div id="l1123" class="code_block">                   A = c
</div><div id="l1124" class="code_block">
</div><div id="l1125" class="code_block">                   | ?- arg(3, X(a,b,c), A).
</div><div id="l1126" class="code_block">                   X = <span class="nb">_</span>595820 
</div><div id="l1127" class="code_block">                   A = b 
</div><div id="l1128" class="code_block">
</div><div id="l1129" class="code_block">                   | ?- arg(2, map(f)(a,b), A).
</div><div id="l1130" class="code_block">                   A = a
</div><div id="l1131" class="code_block">
</div><div id="l1132" class="code_block">                   | ?- arg(1, map(f)(a,b), A). 
</div><div id="l1133" class="code_block">                   A = map(f)
</div><div id="l1134" class="code_block">
</div><div id="l1135" class="code_block">                   | ?- arg(1, (a+b)(foo,bar), A).
</div><div id="l1136" class="code_block">                   A = a+b
</div><div id="l1137" class="code_block">     <span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}}</span>
</div><div id="l1138" class="code_block">
</div><div id="l1139" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>arg0(+Index, +Term, ?Argument)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> arg0/3<span class="nb">}}</span>
</div><div id="l1140" class="code_block">    Unifies <span class="nb">{</span><span class="k">\tt</span> Argument<span class="nb">}</span> with the <span class="s">$</span><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> Index}^{th}</span><span class="s">$</span> argument of <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span>
</div><div id="l1141" class="code_block">    if <span class="nb">{</span><span class="k">\tt</span> Index<span class="nb">}</span> <span class="s">$</span><span class="nb">&gt;</span><span class="s">$</span> 0, or with the functor of <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> if <span class="nb">{</span><span class="k">\tt</span> Index<span class="nb">}</span> = 0.
</div><div id="l1142" class="code_block">
</div><div id="l1143" class="code_block"><span class="k">\ournewitem</span><span class="nb">{</span>hilog<span class="k">\_arg</span>(+Index, +Term, ?Argument)<span class="nb">}{</span>HiLog<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> hilog<span class="k">\_arg</span>/3<span class="nb">}}</span>
</div><div id="l1144" class="code_block">    If <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> is a Prolog term, it has the same behaviour as <span class="nb">{</span><span class="k">\tt</span> arg/3<span class="nb">}</span>,
</div><div id="l1145" class="code_block">    but if <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> is a proper HiLog term, <span class="nb">{</span><span class="k">\tt</span> hilog<span class="k">\_arg</span>/3<span class="nb">}</span> unifies 
</div><div id="l1146" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> Argument<span class="nb">}</span> with the 
</div><div id="l1147" class="code_block">    <span class="s">$</span><span class="o">(</span><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> Index}</span><span class="o">+</span><span class="m">1</span><span class="o">)</span><span class="nb">^{th}</span><span class="s">$</span> argument of the Prolog representation of 
</div><div id="l1148" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span><span class="k">\@</span>.  Semantically, <span class="nb">{</span><span class="k">\tt</span> Argument<span class="nb">}</span> is the <span class="s">$</span><span class="nb">{</span><span class="nv">\tt</span><span class="nb"> Index}^{th}</span><span class="s">$</span> 
</div><div id="l1149" class="code_block">    argument to which the <span class="nb">{</span><span class="k">\em</span> HiLog functor<span class="nb">}</span> of <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> is applied.
</div><div id="l1150" class="code_block">    The arguments of the <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> are numbered from~1 upwards. An atomic term 
</div><div id="l1151" class="code_block">    is taken to have <span class="s">$</span><span class="m">0</span><span class="s">$</span> arguments.  
</div><div id="l1152" class="code_block">    
</div><div id="l1153" class="code_block">    Initially, <span class="nb">{</span><span class="k">\tt</span> Index<span class="nb">}</span> must be instantiated to a positive integer and 
</div><div id="l1154" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> to any non-variable Prolog or HiLog term.
</div><div id="l1155" class="code_block">    If the initial conditions are not satisfied or~<span class="s">$</span><span class="nb">I</span><span class="s">$</span> is 
</div><div id="l1156" class="code_block">    out of range, the call quietly fails. Note that like <span class="nb">{</span><span class="k">\tt</span> arg/3<span class="nb">}</span>
</div><div id="l1157" class="code_block">    this predicate does not succeed for <span class="nb">{</span><span class="k">\tt</span> Index<span class="nb">}</span>=0.
</div><div id="l1158" class="code_block">
</div><div id="l1159" class="code_block">    Examples:
</div><div id="l1160" class="code_block">    <span class="nb">{</span><span class="k">\footnotesize</span>
</div><div id="l1161" class="code_block">     <span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1162" class="code_block">                   | ?- hilog<span class="nb">_</span>arg(2, p(a,b), A).
</div><div id="l1163" class="code_block">                   A = b
</div><div id="l1164" class="code_block">
</div><div id="l1165" class="code_block">                   | ?- hilog<span class="nb">_</span>arg(2, h(a,b), A).
</div><div id="l1166" class="code_block">                   A = b
</div><div id="l1167" class="code_block">
</div><div id="l1168" class="code_block">                   | ?- hilog<span class="nb">_</span>arg(3, X(a,b,c), A).
</div><div id="l1169" class="code_block">                   X = <span class="nb">_</span>595820
</div><div id="l1170" class="code_block">                   A = c
</div><div id="l1171" class="code_block">
</div><div id="l1172" class="code_block">                   | ?- hilog<span class="nb">_</span>arg(1, map(f)(a,b), A).
</div><div id="l1173" class="code_block">                   A = a
</div><div id="l1174" class="code_block">
</div><div id="l1175" class="code_block">                   | ?- hilog<span class="nb">_</span>arg(2, map(f)(a,b), A).
</div><div id="l1176" class="code_block">                   A = b
</div><div id="l1177" class="code_block">
</div><div id="l1178" class="code_block">                   | ?- hilog<span class="nb">_</span>arg(1, (a+b)(foo,bar), A).
</div><div id="l1179" class="code_block">                   A = foo
</div><div id="l1180" class="code_block">
</div><div id="l1181" class="code_block">                   | ?- hilog<span class="nb">_</span>arg(1, apply(foo), A). 
</div><div id="l1182" class="code_block">                   A = foo
</div><div id="l1183" class="code_block">
</div><div id="l1184" class="code_block">                   | ?- hilog<span class="nb">_</span>arg(1, apply(foo,bar), A).
</div><div id="l1185" class="code_block">                   A = bar
</div><div id="l1186" class="code_block">     <span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}}</span>
</div><div id="l1187" class="code_block">
</div><div id="l1188" class="code_block">    Note the difference between the last two examples. The difference is 
</div><div id="l1189" class="code_block">    due to the fact that <span class="nb">{</span><span class="k">\tt</span> apply/1<span class="nb">}</span> is a Prolog term, while 
</div><div id="l1190" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> apply/2<span class="nb">}</span> is a proper HiLog term.
</div><div id="l1191" class="code_block">
</div><div id="l1192" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>?Term =.. [?Functor |?ArgList]<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> =../2<span class="nb">}}</span> 
</div><div id="l1193" class="code_block">    Succeeds when <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> is any (Prolog or) HiLog term, <span class="nb">{</span><span class="k">\tt</span> Functor<span class="nb">}</span> is 
</div><div id="l1194" class="code_block">    its Prolog functor and <span class="nb">{</span><span class="k">\tt</span> ArgList<span class="nb">}</span> is the list of its arguments. 
</div><div id="l1195" class="code_block">    The use of <span class="nb">{</span><span class="k">\tt</span> =../2<span class="nb">}</span> (pronounced <span class="nb">{</span><span class="k">\em</span> univ<span class="nb">}</span>) although convenient, 
</div><div id="l1196" class="code_block">    can nearly always be avoided.
</div><div id="l1197" class="code_block">    Whenever efficiency is critical, it is advisable to use the
</div><div id="l1198" class="code_block">    predicates <span class="nb">{</span><span class="k">\tt</span> functor/3<span class="nb">}</span> and <span class="nb">{</span><span class="k">\tt</span> arg/3<span class="nb">}</span>, since <span class="nb">{</span><span class="k">\tt</span> =../2<span class="nb">}</span> is 
</div><div id="l1199" class="code_block">    implemented by calls to these predicates.  The behaviour of 
</div><div id="l1200" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> =../2<span class="nb">}</span> is as follows:
</div><div id="l1201" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l1202" class="code_block">    <span class="k">\item</span> If initially <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> is uninstantiated, then the list in the 
</div><div id="l1203" class="code_block">          second argument of <span class="nb">{</span><span class="k">\tt</span> =../2<span class="nb">}</span> must be instantiated either to a
</div><div id="l1204" class="code_block">          <span class="nb">{</span><span class="k">\em</span> proper list<span class="nb">}</span> (list of determinate length) whose head is an 
</div><div id="l1205" class="code_block">          atom, or to a list of length 1 whose head is a number.
</div><div id="l1206" class="code_block">    <span class="k">\item</span> If the arguments of <span class="nb">{</span><span class="k">\tt</span> =../2<span class="nb">}</span> are both uninstantiated, or if 
</div><div id="l1207" class="code_block">          either of them is not what is expected, <span class="nb">{</span><span class="k">\tt</span> =../2<span class="nb">}</span> aborts, 
</div><div id="l1208" class="code_block">          producing an appropriate error message.
</div><div id="l1209" class="code_block">    <span class="k">\end</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l1210" class="code_block">
</div><div id="l1211" class="code_block">    Examples:
</div><div id="l1212" class="code_block">    <span class="nb">{</span><span class="k">\footnotesize</span>
</div><div id="l1213" class="code_block">     <span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1214" class="code_block">                   | ?- X - 1 =.. L.
</div><div id="l1215" class="code_block">                   X = <span class="nb">_</span>595692
</div><div id="l1216" class="code_block">                   L = [-,<span class="nb">_</span>595692,1]
</div><div id="l1217" class="code_block">
</div><div id="l1218" class="code_block">                   | ?- p(a,b,c) =.. L.
</div><div id="l1219" class="code_block">                   L = [p,a,b,c]
</div><div id="l1220" class="code_block">
</div><div id="l1221" class="code_block">                   | ?- h(a,b,c) =.. L.
</div><div id="l1222" class="code_block">                   L = [apply,h,a,b,c]
</div><div id="l1223" class="code_block">
</div><div id="l1224" class="code_block">                   | ?- map(p)(a,b) =.. L.
</div><div id="l1225" class="code_block">                   L = [apply,map(p),a,b]
</div><div id="l1226" class="code_block">
</div><div id="l1227" class="code_block">                   | ?- T =.. [foo].
</div><div id="l1228" class="code_block">                   T = foo
</div><div id="l1229" class="code_block">
</div><div id="l1230" class="code_block">                   | ?- T =.. [3|X].
</div><div id="l1231" class="code_block">                   T = 3
</div><div id="l1232" class="code_block">                   X = []
</div><div id="l1233" class="code_block">
</div><div id="l1234" class="code_block">                   | ?- T =.. [apply,X,a,b].
</div><div id="l1235" class="code_block">                   T = apply(X,a,b)
</div><div id="l1236" class="code_block">
</div><div id="l1237" class="code_block">                   | ?- T =.. [1,2].
</div><div id="l1238" class="code_block">                   ++Error: Wrong type(s) in argument 2 of =../2
</div><div id="l1239" class="code_block">                   Aborting...
</div><div id="l1240" class="code_block">
</div><div id="l1241" class="code_block">                   | ?- T =.. [a+b,2].
</div><div id="l1242" class="code_block">                   ++Error: Wrong type(s) in argument 2 of =../2
</div><div id="l1243" class="code_block">                   Aborting..
</div><div id="l1244" class="code_block">
</div><div id="l1245" class="code_block">                   | ?- X =.. [foo|Y].
</div><div id="l1246" class="code_block">                   ++Error: Argument 2 of =../2 is not a proper list
</div><div id="l1247" class="code_block">                   Aborting...
</div><div id="l1248" class="code_block">     <span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}}</span>
</div><div id="l1249" class="code_block">
</div><div id="l1250" class="code_block">     Exceptions:
</div><div id="l1251" class="code_block">     <span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l1252" class="code_block">     <span class="k">\item</span><span class="na">[{\tt instantiation\_error}]</span>
</div><div id="l1253" class="code_block">	Argument 2 of <span class="nb">{</span><span class="k">\tt</span> =../2<span class="nb">}</span> is not a proper list.
</div><div id="l1254" class="code_block">     <span class="k">\item</span><span class="na">[{\tt type\_error}]</span>
</div><div id="l1255" class="code_block">	Head of argument 2 of <span class="nb">{</span><span class="k">\tt</span> =../2<span class="nb">}</span> is not an atom or number.
</div><div id="l1256" class="code_block">     <span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l1257" class="code_block">
</div><div id="l1258" class="code_block"><span class="c">%in the following line I used a very ``dirty&#39;&#39; LaTeX hack! -- Kostis.</span>
</div><div id="l1259" class="code_block">
</div><div id="l1260" class="code_block"><span class="k">\ournewitem</span><span class="nb">{</span>?Term <span class="k">\^</span><span class="nb">{</span> <span class="nb">}</span>=.. [?F |?ArgList]<span class="nb">}{</span>HiLog<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> <span class="k">\^</span><span class="nb">{</span> <span class="nb">}</span>=../2<span class="nb">}}</span> 
</div><div id="l1261" class="code_block">    When <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> is a Prolog term, this predicate behaves exactly like
</div><div id="l1262" class="code_block">    the Prolog <span class="nb">{</span><span class="k">\tt</span> =../2<span class="nb">}</span>. However when <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> is a proper HiLog term, 
</div><div id="l1263" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> <span class="k">\verb</span>|<span class="nb">^</span>|=../2<span class="nb">}</span> 
</div><div id="l1264" class="code_block">    succeeds unifying <span class="nb">{</span><span class="k">\tt</span> F<span class="nb">}</span> to its HiLog functor and <span class="nb">{</span><span class="k">\tt</span> ArgList<span class="nb">}</span> to the 
</div><div id="l1265" class="code_block">    list of the arguments to which this HiLog functor is applied. Like 
</div><div id="l1266" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> =../2<span class="nb">}</span>, the use of <span class="nb">{</span><span class="k">\tt</span> <span class="k">\verb</span>|<span class="nb">^</span>|=../2<span class="nb">}</span> can nearly always be avoided
</div><div id="l1267" class="code_block">    by using the more efficient predicates <span class="nb">{</span><span class="k">\tt</span> hilog<span class="k">\_functor</span>/3<span class="nb">}</span> and 
</div><div id="l1268" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> hilog<span class="k">\_arg</span>/3<span class="nb">}</span>. The behaviour of <span class="nb">{</span><span class="k">\tt</span> <span class="k">\verb</span>|<span class="nb">^</span>|=../2<span class="nb">}</span>, on HiLog terms 
</div><div id="l1269" class="code_block">    is as follows:
</div><div id="l1270" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l1271" class="code_block">    <span class="k">\item</span> If initially <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> is uninstantiated, then the list in the 
</div><div id="l1272" class="code_block">          second argument of <span class="nb">{</span><span class="k">\tt</span> <span class="k">\verb</span>|<span class="nb">^</span>|=../2<span class="nb">}</span> must be instantiated to 
</div><div id="l1273" class="code_block">          a <span class="nb">{</span><span class="k">\em</span> proper list<span class="nb">}</span> (list of determinate length) whose head can 
</div><div id="l1274" class="code_block">          be any Prolog or HiLog term.
</div><div id="l1275" class="code_block">    <span class="k">\item</span> If the arguments of <span class="nb">{</span><span class="k">\tt</span> <span class="k">\verb</span>|<span class="nb">^</span>|=../2<span class="nb">}</span> are both uninstantiated, 
</div><div id="l1276" class="code_block">          or if the second of them is not what is expected, 
</div><div id="l1277" class="code_block">          <span class="nb">{</span><span class="k">\tt</span> <span class="k">\verb</span>|<span class="nb">^</span>|=../2<span class="nb">}</span> aborts, producing an appropriate error message.
</div><div id="l1278" class="code_block">    <span class="k">\end</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l1279" class="code_block">    Examples:
</div><div id="l1280" class="code_block">    <span class="nb">{</span><span class="k">\footnotesize</span>
</div><div id="l1281" class="code_block">     <span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1282" class="code_block">                   | ?- p(a,b,c) <span class="nb">^</span>=.. L.
</div><div id="l1283" class="code_block">                   L = [p,a,b,c]
</div><div id="l1284" class="code_block">
</div><div id="l1285" class="code_block">                   | ?- h(a,b,c) <span class="nb">^</span>=.. L.
</div><div id="l1286" class="code_block">                   L = [h,a,b,c]
</div><div id="l1287" class="code_block">
</div><div id="l1288" class="code_block">                   | ?- map(p)(a,b) <span class="nb">^</span>=.. L.
</div><div id="l1289" class="code_block">                   L = [map(p),a,b]
</div><div id="l1290" class="code_block">
</div><div id="l1291" class="code_block">                   | ?- T <span class="nb">^</span>=.. [X,a,b].
</div><div id="l1292" class="code_block">                   T = apply(X,a,b)
</div><div id="l1293" class="code_block">
</div><div id="l1294" class="code_block">                   | ?- T <span class="nb">^</span>=.. [2,2].
</div><div id="l1295" class="code_block">                   T = apply(2,2)
</div><div id="l1296" class="code_block">
</div><div id="l1297" class="code_block">                   | ?- T <span class="nb">^</span>=.. [a+b,2].
</div><div id="l1298" class="code_block">                   T = apply(a+b,2)
</div><div id="l1299" class="code_block">
</div><div id="l1300" class="code_block">                   | ?- T <span class="nb">^</span>=.. [3|X].
</div><div id="l1301" class="code_block">                   ++Error: Argument 2 of <span class="nb">^</span>=../2 is not a proper list
</div><div id="l1302" class="code_block">                   Aborting...
</div><div id="l1303" class="code_block">     <span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}}</span>
</div><div id="l1304" class="code_block">
</div><div id="l1305" class="code_block">     Exceptions:
</div><div id="l1306" class="code_block">     <span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l1307" class="code_block">     <span class="k">\item</span><span class="na">[{\tt instantiation\_error}]</span>
</div><div id="l1308" class="code_block">	Argument 2 of <span class="nb">{</span><span class="k">\tt</span> <span class="k">\verb</span>|<span class="nb">^</span>|=../2<span class="nb">}</span> is not a proper list.
</div><div id="l1309" class="code_block">     <span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l1310" class="code_block">
</div><div id="l1311" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>copy<span class="k">\_term</span>(+Term, -Copy)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> copy<span class="k">\_term</span>/2<span class="nb">}}</span>
</div><div id="l1312" class="code_block">    Makes a <span class="nb">{</span><span class="k">\tt</span> Copy<span class="nb">}</span> of <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> in which all variables have been
</div><div id="l1313" class="code_block">    replaced by brand new variables which occur nowhere else. It can
</div><div id="l1314" class="code_block">    be very handy when writing (meta-)interpreters for logic-based
</div><div id="l1315" class="code_block">    languages.  The version of <span class="nb">{</span><span class="k">\tt</span> copy<span class="k">\_term</span>/2<span class="nb">}</span> provided is <span class="nb">{</span><span class="k">\em</span> space
</div><div id="l1316" class="code_block">    efficient<span class="nb">}</span> in the sense that it never copies ground terms. 
</div><div id="l1317" class="code_block">    Predicate <span class="nb">{</span><span class="k">\tt</span> copy<span class="k">\_term</span>/2<span class="nb">}</span> has no associated errors or exceptions.
</div><div id="l1318" class="code_block">
</div><div id="l1319" class="code_block">    Examples:
</div><div id="l1320" class="code_block">    <span class="nb">{</span><span class="k">\footnotesize</span>
</div><div id="l1321" class="code_block">     <span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1322" class="code_block">                   | ?- copy<span class="nb">_</span>term(X, Y).
</div><div id="l1323" class="code_block">
</div><div id="l1324" class="code_block">                   X = <span class="nb">_</span>598948
</div><div id="l1325" class="code_block">                   Y = <span class="nb">_</span>598904
</div><div id="l1326" class="code_block">
</div><div id="l1327" class="code_block">                   | ?- copy<span class="nb">_</span>term(f(a,X), Y).
</div><div id="l1328" class="code_block">
</div><div id="l1329" class="code_block">                   X = <span class="nb">_</span>598892
</div><div id="l1330" class="code_block">                   Y = f(a,<span class="nb">_</span>599112)
</div><div id="l1331" class="code_block">     <span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}}</span>
</div><div id="l1332" class="code_block">
</div><div id="l1333" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>name(?Constant, ?CharList)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> name/2<span class="nb">}}</span> 
</div><div id="l1334" class="code_block">    The standard predicate <span class="nb">{</span><span class="k">\tt</span> name/2<span class="nb">}</span> performs the conversion 
</div><div id="l1335" class="code_block">    between a constant and its character list representation. 
</div><div id="l1336" class="code_block">    If <span class="nb">{</span><span class="k">\tt</span> Constant<span class="nb">}</span> is supplied (and is any atom or number), <span class="nb">{</span><span class="k">\tt</span> CharList<span class="nb">}</span> 
</div><div id="l1337" class="code_block">    is unified with a list of ASCII codes representing the <span class="nb">{</span><span class="k">\em</span> ``name&#39;&#39;<span class="nb">}</span> 
</div><div id="l1338" class="code_block">    of the constant.  In that case, <span class="nb">{</span><span class="k">\tt</span> CharList<span class="nb">}</span> is exactly the list of 
</div><div id="l1339" class="code_block">    ASCII character codes that appear in the printed representation of 
</div><div id="l1340" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> Constant<span class="nb">}</span><span class="k">\@</span>.  If on the other hand <span class="nb">{</span><span class="k">\tt</span> Constant<span class="nb">}</span> is a variable, 
</div><div id="l1341" class="code_block">    then <span class="nb">{</span><span class="k">\tt</span> CharList<span class="nb">}</span> must be a proper list of ASCII character codes. 
</div><div id="l1342" class="code_block">    In that case, <span class="nb">{</span><span class="k">\tt</span> name/2<span class="nb">}</span> will convert a list of ASCII characters 
</div><div id="l1343" class="code_block">    that can represent a number to a number rather than to a character string.
</div><div id="l1344" class="code_block">    As a consequence of this, there are some atoms (for example <span class="k">\verb</span>|&#39;18&#39;|)
</div><div id="l1345" class="code_block">    which cannot be constructed by using <span class="nb">{</span><span class="k">\tt</span> name/2<span class="nb">}</span><span class="k">\@</span>. 
</div><div id="l1346" class="code_block">    If conversion to an atom is preferred in these cases, the 
</div><div id="l1347" class="code_block">    standard predicate <span class="nb">{</span><span class="k">\tt</span> atom<span class="k">\_codes</span>/2<span class="nb">}</span> should be used instead. The 
</div><div id="l1348" class="code_block">    syntax for numbers that is accepted by <span class="nb">{</span><span class="k">\tt</span> name/2<span class="nb">}</span> is exactly the one 
</div><div id="l1349" class="code_block">    which <span class="nb">{</span><span class="k">\tt</span> read/1<span class="nb">}</span> accepts.  Predicate <span class="nb">{</span><span class="k">\tt</span> name/2<span class="nb">}</span> is provided for 
</div><div id="l1350" class="code_block">    backwards compatibility.  It is advisable that new programs use
</div><div id="l1351" class="code_block">    the predicates <span class="nb">{</span><span class="k">\tt</span> atom<span class="k">\_codes</span>/2<span class="nb">}</span> and <span class="nb">{</span><span class="k">\tt</span> number<span class="k">\_codes</span>/2<span class="nb">}</span> described
</div><div id="l1352" class="code_block">    below.
</div><div id="l1353" class="code_block">
</div><div id="l1354" class="code_block">    In <span class="k">\version\</span> predicate <span class="nb">{</span><span class="k">\tt</span> name/2<span class="nb">}</span> is not yet implemented for 
</div><div id="l1355" class="code_block">    converting from a real number to its character list representation, 
</div><div id="l1356" class="code_block">    and if the representation of a real is provided as <span class="nb">{</span><span class="k">\tt</span> CharList<span class="nb">}</span>, 
</div><div id="l1357" class="code_block">    it will be converted to an atom.
</div><div id="l1358" class="code_block">
</div><div id="l1359" class="code_block">    If both of the arguments of <span class="nb">{</span><span class="k">\tt</span> name/2<span class="nb">}</span> are uninstantiated or 
</div><div id="l1360" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> CharList<span class="nb">}</span> is not a proper list of ASCII characters, <span class="nb">{</span><span class="k">\tt</span> name/2<span class="nb">}</span> 
</div><div id="l1361" class="code_block">    will abort and an error message will be sent to the standard error stream.
</div><div id="l1362" class="code_block">
</div><div id="l1363" class="code_block">    Examples:
</div><div id="l1364" class="code_block">    <span class="nb">{</span><span class="k">\footnotesize</span>
</div><div id="l1365" class="code_block">     <span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1366" class="code_block">                   | ?- name(&#39;Foo&#39;, L).
</div><div id="l1367" class="code_block">                   L = [70,111,111]
</div><div id="l1368" class="code_block">
</div><div id="l1369" class="code_block">                   | ?- name([], L).
</div><div id="l1370" class="code_block">                   L = [91,93]
</div><div id="l1371" class="code_block">
</div><div id="l1372" class="code_block">                   | ?- name(431, L).
</div><div id="l1373" class="code_block">                   L = [52,51,49]
</div><div id="l1374" class="code_block">
</div><div id="l1375" class="code_block">                   | ?- name(X, [102,111,111]).
</div><div id="l1376" class="code_block">                   X = foo
</div><div id="l1377" class="code_block"> 
</div><div id="l1378" class="code_block">                   | ?- name(X, []).
</div><div id="l1379" class="code_block">                   X = &#39;&#39;
</div><div id="l1380" class="code_block">
</div><div id="l1381" class="code_block">                   | ?- name(X, &quot;Foo&quot;).
</div><div id="l1382" class="code_block">                   X = &#39;Foo&#39;
</div><div id="l1383" class="code_block">
</div><div id="l1384" class="code_block">                   | ?- name(X, [52,51,49]).
</div><div id="l1385" class="code_block">                   X = 431
</div><div id="l1386" class="code_block">
</div><div id="l1387" class="code_block">                   | ?- name(X, [45,48,50,49,51]), integer(X).
</div><div id="l1388" class="code_block">                   X = -213
</div><div id="l1389" class="code_block">
</div><div id="l1390" class="code_block">                   | ?- name(3.14, L).
</div><div id="l1391" class="code_block">                   ++Error: Predicate name/2 for reals is not implemented yet
</div><div id="l1392" class="code_block">                   Aborting...
</div><div id="l1393" class="code_block">     <span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}}</span>
</div><div id="l1394" class="code_block">
</div><div id="l1395" class="code_block">     Exceptions:
</div><div id="l1396" class="code_block">     <span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l1397" class="code_block">     <span class="k">\item</span><span class="na">[{\tt instantiation\_error}]</span>
</div><div id="l1398" class="code_block">	Both arguments are uninstantiated, or argument 2 of <span class="nb">{</span><span class="k">\tt</span> name/2<span class="nb">}</span> 
</div><div id="l1399" class="code_block">	contains a variable or is not a proper list.
</div><div id="l1400" class="code_block">     <span class="k">\item</span><span class="na">[{\tt type\_error}]</span>
</div><div id="l1401" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> Constant<span class="nb">}</span> is not a variable, an atom or a number.
</div><div id="l1402" class="code_block">     <span class="k">\item</span><span class="na">[{\tt range\_error}]</span>
</div><div id="l1403" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> CharList<span class="nb">}</span> is not a list of ASCII characters.
</div><div id="l1404" class="code_block">     <span class="k">\item</span><span class="na">[{\tt implementation\_error}]</span>
</div><div id="l1405" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> Constant<span class="nb">}</span> is a real number (conversion from a real to its 
</div><div id="l1406" class="code_block">	character list representation is not implemented yet).
</div><div id="l1407" class="code_block">     <span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l1408" class="code_block">
</div><div id="l1409" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>atom<span class="k">\_codes</span>(?Atom, ?CharCodeList)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> atom<span class="k">\_codes</span>/2<span class="nb">}}</span> 
</div><div id="l1410" class="code_block">    The standard predicate <span class="nb">{</span><span class="k">\tt</span> atom<span class="k">\_codes</span>/2<span class="nb">}</span> performs the conversion 
</div><div id="l1411" class="code_block">    between an atom and its character list representation. 
</div><div id="l1412" class="code_block">    If <span class="nb">{</span><span class="k">\tt</span> Atom<span class="nb">}</span> is supplied (and is an atom), <span class="nb">{</span><span class="k">\tt</span> CharList<span class="nb">}</span> 
</div><div id="l1413" class="code_block">    is unified with a list of ASCII codes representing the <span class="nb">{</span><span class="k">\em</span> ``name&#39;&#39;<span class="nb">}</span> 
</div><div id="l1414" class="code_block">    of that atom.  In that case, <span class="nb">{</span><span class="k">\tt</span> CharList<span class="nb">}</span> is exactly the list of 
</div><div id="l1415" class="code_block">    ASCII character codes that appear in the printed representation of 
</div><div id="l1416" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> Atom<span class="nb">}</span>.  If on the other hand <span class="nb">{</span><span class="k">\tt</span> Atom<span class="nb">}</span> is a variable, 
</div><div id="l1417" class="code_block">    then <span class="nb">{</span><span class="k">\tt</span> CharList<span class="nb">}</span> must be a proper list of ASCII character codes. 
</div><div id="l1418" class="code_block">    In that case, <span class="nb">{</span><span class="k">\tt</span> Atom<span class="nb">}</span> is instantiated to an atom containing
</div><div id="l1419" class="code_block">    exactly those characters, even if the characters look like the
</div><div id="l1420" class="code_block">    printed representation of a number.
</div><div id="l1421" class="code_block">
</div><div id="l1422" class="code_block">    If both of the arguments of <span class="nb">{</span><span class="k">\tt</span> atom<span class="k">\_codes</span>/2<span class="nb">}</span> are uninstantiated or
</div><div id="l1423" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> CharList<span class="nb">}</span> is not a proper list of ASCII characters, <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1424" class="code_block">    atom<span class="k">\_codes</span>/2<span class="nb">}</span> aborts, and an error message will be sent to
</div><div id="l1425" class="code_block">    the standard error stream.
</div><div id="l1426" class="code_block">
</div><div id="l1427" class="code_block">    Examples:
</div><div id="l1428" class="code_block">    <span class="nb">{</span><span class="k">\footnotesize</span>
</div><div id="l1429" class="code_block">     <span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1430" class="code_block">                   | ?- atom<span class="nb">_</span>codes(&#39;Foo&#39;, L).
</div><div id="l1431" class="code_block">                   L = [70,111,111]
</div><div id="l1432" class="code_block">
</div><div id="l1433" class="code_block">                   | ?- atom<span class="nb">_</span>codes([], L).
</div><div id="l1434" class="code_block">                   L = [91,93]
</div><div id="l1435" class="code_block">
</div><div id="l1436" class="code_block">                   | ?- atom<span class="nb">_</span>codes(X, [102,111,111]).
</div><div id="l1437" class="code_block">                   X = foo
</div><div id="l1438" class="code_block"> 
</div><div id="l1439" class="code_block">                   | ?- atom<span class="nb">_</span>codes(X, []).
</div><div id="l1440" class="code_block">                   X = &#39;&#39;
</div><div id="l1441" class="code_block">
</div><div id="l1442" class="code_block">                   | ?- atom<span class="nb">_</span>codes(X, &quot;Foo&quot;).
</div><div id="l1443" class="code_block">                   X = &#39;Foo&#39;
</div><div id="l1444" class="code_block">
</div><div id="l1445" class="code_block">                   | ?- atom<span class="nb">_</span>codes(X, [52,51,49]).
</div><div id="l1446" class="code_block">                   X = &#39;431&#39;
</div><div id="l1447" class="code_block">
</div><div id="l1448" class="code_block">                   | ?- atom<span class="nb">_</span>codes(X, [52,51,49]), integer(X).
</div><div id="l1449" class="code_block">                   no
</div><div id="l1450" class="code_block">
</div><div id="l1451" class="code_block">                   | ?- atom<span class="nb">_</span>codes(X, [52,Y,49]).
</div><div id="l1452" class="code_block">                   ! Instantiation error in argument 2 of atom<span class="nb">_</span>codes/2
</div><div id="l1453" class="code_block">                   ! Aborting...
</div><div id="l1454" class="code_block">
</div><div id="l1455" class="code_block">                   | ?- atom<span class="nb">_</span>codes(431, L).
</div><div id="l1456" class="code_block">                   ! Type error: in argument 1 of atom<span class="nb">_</span>codes/2
</div><div id="l1457" class="code_block">                   ! atom expected, but something else found
</div><div id="l1458" class="code_block">                   ! Aborting...
</div><div id="l1459" class="code_block">
</div><div id="l1460" class="code_block">                   | ?- atom<span class="nb">_</span>codes(X, [52,300,49]).
</div><div id="l1461" class="code_block">                   ! Range error: in argument 2 of atom<span class="nb">_</span>codes/2
</div><div id="l1462" class="code_block">                   ! ASCII code expected, but 300 found
</div><div id="l1463" class="code_block">                   ! Aborting...
</div><div id="l1464" class="code_block">     <span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}}</span>
</div><div id="l1465" class="code_block">
</div><div id="l1466" class="code_block">    Exceptions:
</div><div id="l1467" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l1468" class="code_block">    <span class="k">\item</span><span class="na">[{\tt instantiation\_error}]</span>
</div><div id="l1469" class="code_block">	Both arguments are uninstantiated, or argument 2
</div><div id="l1470" class="code_block">	is not a proper list, or it contains a variable.
</div><div id="l1471" class="code_block">    <span class="k">\item</span><span class="na">[{\tt type\_error}]</span>
</div><div id="l1472" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> Atom<span class="nb">}</span> is not a variable or an atom.
</div><div id="l1473" class="code_block">    <span class="k">\item</span><span class="na">[{\tt range\_error}]</span>
</div><div id="l1474" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> CharList<span class="nb">}</span> is not a list of ASCII characters.
</div><div id="l1475" class="code_block">    <span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l1476" class="code_block">
</div><div id="l1477" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>atom<span class="k">\_chars</span>(?Number, ?CharAtomList)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> atom<span class="k">\_chars</span>/2<span class="nb">}}</span> 
</div><div id="l1478" class="code_block">    Like <span class="k">\verb</span>|atom<span class="nb">_</span>codes|, but the list returned (or input) is a list of
</div><div id="l1479" class="code_block">    characters <span class="k">\emph</span><span class="nb">{</span>as atoms<span class="nb">}</span> rather than ASCII codes. For instance, 
</div><div id="l1480" class="code_block">    <span class="k">\verb</span>|atom<span class="nb">_</span>chars(abc,X)| binds <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> to the list <span class="nb">{</span><span class="k">\tt</span> [a,b,c]<span class="nb">}</span>
</div><div id="l1481" class="code_block">    instead of <span class="nb">{</span><span class="k">\tt</span> [97,98,99]<span class="nb">}</span>.
</div><div id="l1482" class="code_block">
</div><div id="l1483" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>number<span class="k">\_codes</span>(?Number, ?CharCodeList)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> number<span class="k">\_codes</span>/2<span class="nb">}}</span> 
</div><div id="l1484" class="code_block">    The standard predicate <span class="nb">{</span><span class="k">\tt</span> number<span class="k">\_codes</span>/2<span class="nb">}</span> performs the conversion 
</div><div id="l1485" class="code_block">    between a number and its character list representation. 
</div><div id="l1486" class="code_block">    If <span class="nb">{</span><span class="k">\tt</span> Number<span class="nb">}</span> is supplied (and is a number), <span class="nb">{</span><span class="k">\tt</span> CharList<span class="nb">}</span> is
</div><div id="l1487" class="code_block">    unified with a list of ASCII codes comprising the printed representation
</div><div id="l1488" class="code_block">    of that <span class="nb">{</span><span class="k">\tt</span> Number<span class="nb">}</span>.  If on the other hand <span class="nb">{</span><span class="k">\tt</span> Number<span class="nb">}</span> is a variable, 
</div><div id="l1489" class="code_block">    then <span class="nb">{</span><span class="k">\tt</span> CharList<span class="nb">}</span> must be a proper list of ASCII character codes that
</div><div id="l1490" class="code_block">    corresponds to the correct syntax of a number (either integer or float)
</div><div id="l1491" class="code_block">    In that case, <span class="nb">{</span><span class="k">\tt</span> Number<span class="nb">}</span> is instantiated to that number, otherwise
</div><div id="l1492" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> number<span class="k">\_codes</span>/2<span class="nb">}</span> will simply fail.
</div><div id="l1493" class="code_block">
</div><div id="l1494" class="code_block">    If both of the arguments of <span class="nb">{</span><span class="k">\tt</span> number<span class="k">\_codes</span>/2<span class="nb">}</span> are uninstantiated or
</div><div id="l1495" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> CharList<span class="nb">}</span> is not a proper list of ASCII characters, <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1496" class="code_block">    number<span class="k">\_codes</span>/2<span class="nb">}</span> aborts, and an error message will be sent to
</div><div id="l1497" class="code_block">    the standard error stream.
</div><div id="l1498" class="code_block">
</div><div id="l1499" class="code_block">    Examples:
</div><div id="l1500" class="code_block">    <span class="nb">{</span><span class="k">\footnotesize</span>
</div><div id="l1501" class="code_block">     <span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1502" class="code_block">                   | ?- number<span class="nb">_</span>codes(123, L).
</div><div id="l1503" class="code_block">                   L = [49,50,51];
</div><div id="l1504" class="code_block">
</div><div id="l1505" class="code_block">                   | ?- number<span class="nb">_</span>codes(N, [49,50,51]), integer(N).
</div><div id="l1506" class="code_block">                   N = 123
</div><div id="l1507" class="code_block">
</div><div id="l1508" class="code_block">                   | ?- number<span class="nb">_</span>codes(31.4e+10, L).
</div><div id="l1509" class="code_block">                   L = [51,46,49,51,57,57,57,55,69,43,49,48]
</div><div id="l1510" class="code_block">
</div><div id="l1511" class="code_block">                   | ?- number<span class="nb">_</span>codes(N, &quot;314e+8&quot;).
</div><div id="l1512" class="code_block">                   N = 3.14e+10
</div><div id="l1513" class="code_block">
</div><div id="l1514" class="code_block">                   | ?- number<span class="nb">_</span>codes(foo, L).
</div><div id="l1515" class="code_block">                   ! Type error: in argument 1 of number<span class="nb">_</span>codes/2
</div><div id="l1516" class="code_block">                   ! number expected, but something else found
</div><div id="l1517" class="code_block">                   ! Aborting...
</div><div id="l1518" class="code_block">     <span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}}</span>
</div><div id="l1519" class="code_block">
</div><div id="l1520" class="code_block">    Exceptions:
</div><div id="l1521" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l1522" class="code_block">    <span class="k">\item</span><span class="na">[{\tt instantiation\_error}]</span>
</div><div id="l1523" class="code_block">	Both arguments are uninstantiated, or argument 2
</div><div id="l1524" class="code_block">	is not a proper list, or it contains a variable.
</div><div id="l1525" class="code_block">    <span class="k">\item</span><span class="na">[{\tt type\_error}]</span>
</div><div id="l1526" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> Number<span class="nb">}</span> is not a variable or a number.
</div><div id="l1527" class="code_block">    <span class="k">\item</span><span class="na">[{\tt range\_error}]</span>
</div><div id="l1528" class="code_block">	<span class="nb">{</span><span class="k">\tt</span> CharList<span class="nb">}</span> is not a list of ASCII characters.
</div><div id="l1529" class="code_block">    <span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l1530" class="code_block">
</div><div id="l1531" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>number<span class="k">\_chars</span>(?Number, ?CharAtomList)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> number<span class="k">\_chars</span>/2<span class="nb">}}</span> 
</div><div id="l1532" class="code_block">    Like <span class="k">\verb</span>|number<span class="nb">_</span>codes|, but the list returned (or input) is a list of
</div><div id="l1533" class="code_block">    characters <span class="k">\emph</span><span class="nb">{</span>as atoms<span class="nb">}</span> rather than ASCII codes. For instance, 
</div><div id="l1534" class="code_block">    <span class="k">\verb</span>|number<span class="nb">_</span>chars(123,X)| binds <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> to the list <span class="nb">{</span><span class="k">\tt</span> [&#39;1&#39;,&#39;2&#39;,&#39;3&#39;]<span class="nb">}</span>
</div><div id="l1535" class="code_block">    instead of <span class="nb">{</span><span class="k">\tt</span> [49,50,51]<span class="nb">}</span>.
</div><div id="l1536" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>number<span class="k">\_digits</span>(?Number, ?DigitList)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> number<span class="k">\_digits</span>/2<span class="nb">}}</span> 
</div><div id="l1537" class="code_block">    Like <span class="k">\verb</span>|number<span class="nb">_</span>chars|, but the list returned (or input) is a list of
</div><div id="l1538" class="code_block">    digits <span class="k">\emph</span><span class="nb">{</span>as numbers<span class="nb">}</span> rather than ASCII codes (for floats, the atom
</div><div id="l1539" class="code_block">    &#39;.&#39;, &#39;+&#39; or &#39;-&#39;, and &#39;e&#39; will also be present in the list). For instance, 
</div><div id="l1540" class="code_block">    <span class="k">\verb</span>|number<span class="nb">_</span>digits(123,X)| binds <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> to the list <span class="nb">{</span><span class="k">\tt</span> [1,2,3]<span class="nb">}</span>
</div><div id="l1541" class="code_block">    instead of <span class="nb">{</span><span class="k">\tt</span> [&#39;1&#39;,&#39;2&#39;,&#39;3&#39;]<span class="nb">}</span>, and <span class="k">\verb</span>|number<span class="nb">_</span>digits(123.45,X)|
</div><div id="l1542" class="code_block">    binds <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> to <span class="nb">{</span><span class="k">\tt</span> [1,.,2,3,4,5,0,0,e,+,0,2]<span class="nb">}</span>.
</div><div id="l1543" class="code_block">
</div><div id="l1544" class="code_block">
</div><div id="l1545" class="code_block"><span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l1546" class="code_block">
</div><div id="l1547" class="code_block">
</div><div id="l1548" class="code_block"><span class="k">\section</span><span class="nb">{</span>All Solutions and Aggregate Predicates<span class="nb">}</span>
</div><div id="l1549" class="code_block"><span class="k">\index</span><span class="nb">{</span>sets, bags<span class="nb">}</span> <span class="k">\index</span><span class="nb">{</span>aggregate predicates!prolog<span class="nb">}</span>
</div><div id="l1550" class="code_block"><span class="c">%-----------------------------------------------------</span>
</div><div id="l1551" class="code_block">Often there are many solutions to a problem and it is necessary
</div><div id="l1552" class="code_block">somehow to compare these solutions with one another.  The most general
</div><div id="l1553" class="code_block">way of doing this is to collect all the solutions into a list, which
</div><div id="l1554" class="code_block">may then be processed in any way desired.  So XSB provides
</div><div id="l1555" class="code_block">ISO-standard predicates such as <span class="nb">{</span><span class="k">\tt</span> setof/3<span class="nb">}</span>, <span class="nb">{</span><span class="k">\tt</span> bagof/3<span class="nb">}</span>, and <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1556" class="code_block">findall/3<span class="nb">}</span> to collect solutions into lists.  Sometimes however, one
</div><div id="l1557" class="code_block">wants simply to perform some aggregate operation over the set of
</div><div id="l1558" class="code_block">solutions, for example to find the maximum or minimum of the set of
</div><div id="l1559" class="code_block">solutions.  XSB uses tabling and HiLog to provide a general and
</div><div id="l1560" class="code_block">powerful aggregation facility as discussed in Section
</div><div id="l1561" class="code_block"><span class="k">\ref</span><span class="nb">{</span>tabling<span class="nb">_</span>aggregate<span class="nb">_</span>predicates<span class="nb">}</span>.
</div><div id="l1562" class="code_block">
</div><div id="l1563" class="code_block"><span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l1564" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>setof(?X, +Goal, ?Set)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> setof/3<span class="nb">}}</span>
</div><div id="l1565" class="code_block">    This predicate may be read as ``<span class="nb">{</span><span class="k">\tt</span> Set<span class="nb">}</span> is the set of all instances 
</div><div id="l1566" class="code_block">    of <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> such that <span class="nb">{</span><span class="k">\tt</span> Goal<span class="nb">}</span> is provable&#39;&#39;.
</div><div id="l1567" class="code_block">    If~<span class="nb">{</span><span class="k">\tt</span> Goal<span class="nb">}</span> is not provable, <span class="nb">{</span><span class="k">\tt</span> setof/3<span class="nb">}</span> fails.
</div><div id="l1568" class="code_block">    The term <span class="nb">{</span><span class="k">\tt</span> Goal<span class="nb">}</span> specifies a goal or goals as in <span class="nb">{</span><span class="k">\tt</span> call(Goal)<span class="nb">}</span>.
</div><div id="l1569" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> Set<span class="nb">}</span> is a set of terms represented as a list of those terms,
</div><div id="l1570" class="code_block">    without duplicates, in the standard order for terms 
</div><div id="l1571" class="code_block">    (see Section~<span class="k">\ref</span><span class="nb">{</span>Comparison<span class="nb">}</span>).
</div><div id="l1572" class="code_block">    If there are uninstantiated variables in <span class="nb">{</span><span class="k">\tt</span> Goal<span class="nb">}</span> which do not also 
</div><div id="l1573" class="code_block">    appear in <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span>, then a call to this evaluable predicate may backtrack,
</div><div id="l1574" class="code_block">    generating alternative values for~<span class="nb">{</span><span class="k">\tt</span> Set<span class="nb">}</span> corresponding to different
</div><div id="l1575" class="code_block">    instantiations of the free variables of~<span class="nb">{</span><span class="k">\tt</span> Goal<span class="nb">}</span>.
</div><div id="l1576" class="code_block">    Variables occurring in <span class="nb">{</span><span class="k">\tt</span> Goal<span class="nb">}</span> will not be treated as free if they 
</div><div id="l1577" class="code_block">    are explicitly bound within~<span class="nb">{</span><span class="k">\tt</span> Goal<span class="nb">}</span> by an existential quantifier.
</div><div id="l1578" class="code_block">    An existential quantification can be specified as:
</div><div id="l1579" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>center<span class="nb">}</span>
</div><div id="l1580" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> Y <span class="k">\^\</span> G<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span><span class="k">\^</span><span class="nb">}</span>
</div><div id="l1581" class="code_block">    <span class="k">\end</span><span class="nb">{</span>center<span class="nb">}</span>
</div><div id="l1582" class="code_block">    meaning there exists a <span class="nb">{</span><span class="k">\tt</span> Y<span class="nb">}</span> such that <span class="nb">{</span><span class="k">\tt</span> G<span class="nb">}</span> is true,
</div><div id="l1583" class="code_block">    where <span class="nb">{</span><span class="k">\tt</span> Y<span class="nb">}</span> is some Prolog term (usually, a variable).
</div><div id="l1584" class="code_block">  
</div><div id="l1585" class="code_block">    Exceptions: Same as predicate <span class="nb">{</span><span class="k">\tt</span> call/1<span class="nb">}</span>
</div><div id="l1586" class="code_block">		(see Section~<span class="k">\ref</span><span class="nb">{</span>meta<span class="nb">_</span>predicates<span class="nb">}</span>).
</div><div id="l1587" class="code_block">
</div><div id="l1588" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>bagof(?X, +Goal, ?Bag)<span class="nb">}</span> <span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> bagof/3<span class="nb">}}</span>
</div><div id="l1589" class="code_block">    This predicate has the same semantics as <span class="nb">{</span><span class="k">\tt</span> setof/3<span class="nb">}</span> except that the 
</div><div id="l1590" class="code_block">    third argument returns an unordered list that may contain duplicates.
</div><div id="l1591" class="code_block">
</div><div id="l1592" class="code_block">    Exceptions: Same as predicate <span class="nb">{</span><span class="k">\tt</span> call/1<span class="nb">}</span>
</div><div id="l1593" class="code_block">		(see Section~<span class="k">\ref</span><span class="nb">{</span>meta<span class="nb">_</span>predicates<span class="nb">}</span>).
</div><div id="l1594" class="code_block">
</div><div id="l1595" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>findall(?X, +Goal, ?List)<span class="nb">}</span> <span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> findall/3<span class="nb">}}</span>
</div><div id="l1596" class="code_block">    Similar to predicate <span class="nb">{</span><span class="k">\tt</span> bagof/3<span class="nb">}</span>, except that variables in <span class="nb">{</span><span class="k">\tt</span> Goal<span class="nb">}</span>
</div><div id="l1597" class="code_block">    that do not occur in <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> are treated as existential, and alternative
</div><div id="l1598" class="code_block">    lists are not returned for different bindings of such variables.  This
</div><div id="l1599" class="code_block">    makes <span class="nb">{</span><span class="k">\tt</span> findall/3<span class="nb">}</span> deterministic (non-backtrackable).  Unlike
</div><div id="l1600" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> setof/3<span class="nb">}</span> and <span class="nb">{</span><span class="k">\tt</span> bagof/3<span class="nb">}</span>, if <span class="nb">{</span><span class="k">\tt</span> Goal<span class="nb">}</span> is unsatisfiable,
</div><div id="l1601" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> findall/3<span class="nb">}</span> succeeds binding <span class="nb">{</span><span class="k">\tt</span> List<span class="nb">}</span> to the empty list.
</div><div id="l1602" class="code_block">
</div><div id="l1603" class="code_block">    Exceptions: Same as predicate <span class="nb">{</span><span class="k">\tt</span> call/1<span class="nb">}</span>
</div><div id="l1604" class="code_block">		(see Section~<span class="k">\ref</span><span class="nb">{</span>meta<span class="nb">_</span>predicates<span class="nb">}</span>).
</div><div id="l1605" class="code_block">
</div><div id="l1606" class="code_block"><span class="k">\ournewitem</span><span class="nb">{</span>tfindall(?X, +Goal, ?List)<span class="nb">}{</span>Tabling<span class="nb">}</span>
</div><div id="l1607" class="code_block"><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> tfindall/3<span class="nb">}}</span>
</div><div id="l1608" class="code_block"><span class="c">%\predindex{tfindall/3~(L)}</span>
</div><div id="l1609" class="code_block"><span class="k">\label</span><span class="nb">{</span>tfindall/3<span class="nb">}</span>
</div><div id="l1610" class="code_block">
</div><div id="l1611" class="code_block">    <span class="nb">{</span><span class="k">\em</span> Note: <span class="nb">{</span><span class="k">\tt</span> tfindall/3<span class="nb">}</span> may be deprecated in current versions.
</div><div id="l1612" class="code_block">    Please use the predicates described in
</div><div id="l1613" class="code_block">    Section~<span class="k">\ref</span><span class="nb">{</span>tabling<span class="nb">_</span>aggregate<span class="nb">_</span>predicates<span class="nb">}</span> if possible<span class="nb">}</span>.
</div><div id="l1614" class="code_block">
</div><div id="l1615" class="code_block">    Like <span class="nb">{</span><span class="k">\tt</span> findall/3<span class="nb">}</span>, <span class="nb">{</span><span class="k">\tt</span> tfindall/3<span class="nb">}</span> treats all variables in
</div><div id="l1616" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> Goal<span class="nb">}</span> that do not occur in <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> as existential.  However,
</div><div id="l1617" class="code_block">    in <span class="nb">{</span><span class="k">\tt</span> tfindall/3<span class="nb">}</span>, the <span class="nb">{</span><span class="k">\tt</span> Goal<span class="nb">}</span> must be a call to a single
</div><div id="l1618" class="code_block">    tabled predicate.
</div><div id="l1619" class="code_block">	
</div><div id="l1620" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> tfindall/3<span class="nb">}</span> allows the user to build programs that use
</div><div id="l1621" class="code_block">    stratified aggregation.  If the table to <span class="nb">{</span><span class="k">\tt</span> Goal<span class="nb">}</span> is incomplete,
</div><div id="l1622" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> tfindall/3<span class="nb">}</span> suspends until the table has been completed, and
</div><div id="l1623" class="code_block">    only then computes <span class="nb">{</span><span class="k">\tt</span> List<span class="nb">}</span>.  See Chapter~<span class="k">\ref</span><span class="nb">{</span>chap:TablingOverview<span class="nb">}</span>
</div><div id="l1624" class="code_block">    for further discussion of <span class="nb">{</span><span class="k">\tt</span> tfindall/3<span class="nb">}</span>.  Like <span class="nb">{</span><span class="k">\tt</span> findall/3<span class="nb">}</span>,
</div><div id="l1625" class="code_block">    if <span class="nb">{</span><span class="k">\tt</span> Goal<span class="nb">}</span> is unsatisfiable, <span class="nb">{</span><span class="k">\tt</span> tfindall/3<span class="nb">}</span> succeeds binding
</div><div id="l1626" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> List<span class="nb">}</span> to the empty list.
</div><div id="l1627" class="code_block">
</div><div id="l1628" class="code_block">    Some of the differences between predicates <span class="nb">{</span><span class="k">\tt</span> findall/3<span class="nb">}</span> and
</div><div id="l1629" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> tfindall/3<span class="nb">}</span> can be seen from the following example:
</div><div id="l1630" class="code_block">
</div><div id="l1631" class="code_block">    <span class="nb">{</span><span class="k">\footnotesize</span>
</div><div id="l1632" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1633" class="code_block">            | ?- [user].
</div><div id="l1634" class="code_block">            [Compiling user]
</div><div id="l1635" class="code_block">            :- table p/1.
</div><div id="l1636" class="code_block">            p(a).
</div><div id="l1637" class="code_block">            p(b).
</div><div id="l1638" class="code_block">            [user compiled, cpu time used: 0.639 seconds]
</div><div id="l1639" class="code_block">            [user loaded]
</div><div id="l1640" class="code_block">
</div><div id="l1641" class="code_block">            yes
</div><div id="l1642" class="code_block">            | ?- p(X), findall(Y, p(Y), L).
</div><div id="l1643" class="code_block">
</div><div id="l1644" class="code_block">            X = a
</div><div id="l1645" class="code_block">            Y = <span class="nb">_</span>922928
</div><div id="l1646" class="code_block">            L = [a];
</div><div id="l1647" class="code_block">
</div><div id="l1648" class="code_block">            X = b
</div><div id="l1649" class="code_block">            Y = <span class="nb">_</span>922820
</div><div id="l1650" class="code_block">            L = [a,b];
</div><div id="l1651" class="code_block">
</div><div id="l1652" class="code_block">            no
</div><div id="l1653" class="code_block">            | ?- abolish<span class="nb">_</span>all<span class="nb">_</span>tables.
</div><div id="l1654" class="code_block">
</div><div id="l1655" class="code_block">            yes
</div><div id="l1656" class="code_block">            | ?- p(X), tfindall(Y, p(Y), L).
</div><div id="l1657" class="code_block">
</div><div id="l1658" class="code_block">            X = b
</div><div id="l1659" class="code_block">            Y = <span class="nb">_</span>922820
</div><div id="l1660" class="code_block">            L = [b,a];
</div><div id="l1661" class="code_block">
</div><div id="l1662" class="code_block">            X = a
</div><div id="l1663" class="code_block">            Y = <span class="nb">_</span>922820
</div><div id="l1664" class="code_block">            L = [b,a];
</div><div id="l1665" class="code_block">
</div><div id="l1666" class="code_block">            no
</div><div id="l1667" class="code_block">    <span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1668" class="code_block">    <span class="nb">}</span>
</div><div id="l1669" class="code_block">
</div><div id="l1670" class="code_block">    Exceptions: Same as predicate <span class="nb">{</span><span class="k">\tt</span> findall/3<span class="nb">}</span> (see above).  Also:
</div><div id="l1671" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l1672" class="code_block">    <span class="k">\item</span><span class="na">[{\tt table\_error}]</span>
</div><div id="l1673" class="code_block">	Upon execution <span class="nb">{</span><span class="k">\tt</span> Goal<span class="nb">}</span> is not a subgoal of a tabled predicate.
</div><div id="l1674" class="code_block">    <span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l1675" class="code_block">
</div><div id="l1676" class="code_block"><span class="k">\ournewitem</span><span class="nb">{</span>tbagof(?X, +Goal, ?List) / tsetof(?X, +Goal, ?List)<span class="nb">}{</span>Tabling<span class="nb">}</span>
</div><div id="l1677" class="code_block"><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> tsetof/3<span class="nb">}}</span>
</div><div id="l1678" class="code_block"><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> tbagof/3<span class="nb">}}</span>
</div><div id="l1679" class="code_block">
</div><div id="l1680" class="code_block">    <span class="nb">{</span><span class="k">\em</span> Note: <span class="nb">{</span><span class="k">\tt</span> tbagof/3<span class="nb">}</span> and <span class="nb">{</span><span class="k">\tt</span> tsetof/3<span class="nb">}</span> may be deprecated in
</div><div id="l1681" class="code_block">    current versions.  Please use the predicates described in
</div><div id="l1682" class="code_block">    Section~<span class="k">\ref</span><span class="nb">{</span>tabling<span class="nb">_</span>aggregate<span class="nb">_</span>predicates<span class="nb">}</span> if possible.<span class="nb">}</span>
</div><div id="l1683" class="code_block">
</div><div id="l1684" class="code_block">The standard predicates <span class="nb">{</span><span class="k">\tt</span> tbagof/3<span class="nb">}</span> and <span class="nb">{</span><span class="k">\tt</span> tsetof/3<span class="nb">}</span> provide
</div><div id="l1685" class="code_block">tabled versions of <span class="nb">{</span><span class="k">\tt</span> bagof/3<span class="nb">}</span> and <span class="nb">{</span><span class="k">\tt</span> setof/3<span class="nb">}</span> in a similar manner
</div><div id="l1686" class="code_block">to the way in which <span class="nb">{</span><span class="k">\tt</span> tfindall/3<span class="nb">}</span> provides a tabled version of <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1687" class="code_block">findall/3<span class="nb">}</span>.
</div><div id="l1688" class="code_block">
</div><div id="l1689" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>X <span class="k">\^\</span> Goal<span class="nb">}</span>
</div><div id="l1690" class="code_block"><span class="c">%\predindex{$\wedge/2$~(L)}\index{$\wedge/2$|bold}</span>
</div><div id="l1691" class="code_block">    The system recognises this as meaning there exists an <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> such
</div><div id="l1692" class="code_block">    that <span class="nb">{</span><span class="k">\tt</span> Goal<span class="nb">}</span> is true, and treats it as equivalent to <span class="nb">{</span><span class="k">\tt</span> call(Goal)<span class="nb">}</span>.
</div><div id="l1693" class="code_block">    The use of this explicit existential quantifier outside predicates
</div><div id="l1694" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> setof/3<span class="nb">}</span> and <span class="nb">{</span><span class="k">\tt</span> bagof/3<span class="nb">}</span> constructs is superfluous.
</div><div id="l1695" class="code_block"><span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l1696" class="code_block">
</div><div id="l1697" class="code_block"><span class="k">\subsection</span><span class="nb">{</span>Tabling Aggregate Predicates<span class="nb">}</span><span class="k">\label</span><span class="nb">{</span>tabling<span class="nb">_</span>aggregate<span class="nb">_</span>predicates<span class="nb">}</span>
</div><div id="l1698" class="code_block"><span class="c">%-------------------------------------------------------------------------</span>
</div><div id="l1699" class="code_block"><span class="k">\index</span><span class="nb">{</span>aggregate predicates!tabling<span class="nb">}</span> <span class="k">\index</span><span class="nb">{</span>tabling!aggregate predicates<span class="nb">}</span>
</div><div id="l1700" class="code_block"><span class="c">%-------------------------------------------------------------------------</span>
</div><div id="l1701" class="code_block">
</div><div id="l1702" class="code_block">HiLog provides an elegant way to introduce aggregate operations into
</div><div id="l1703" class="code_block"><span class="k">\ourprolog</span>.  HiLog allows a user to define named (and parameterized)
</div><div id="l1704" class="code_block">sets (or bags).  For example, say we have a simple database-like predicate,
</div><div id="l1705" class="code_block"><span class="k">\verb</span>|employee(Name,Dept,Sal)|, which contains a tuple for each
</div><div id="l1706" class="code_block">employee in our concern and contains the employee&#39;s name, department,
</div><div id="l1707" class="code_block">and salary.  From this predicate we can construct a set, or bag
</div><div id="l1708" class="code_block">really, that contains all the salaries of employees in the relation:
</div><div id="l1709" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1710" class="code_block">    :- hilog salaries.
</div><div id="l1711" class="code_block">    salaries(Sal) :- employee(<span class="nb">_</span>Name,<span class="nb">_</span>Dept,Sal).
</div><div id="l1712" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1713" class="code_block">So <span class="k">\verb</span>|salaries| is the name of a unary predicate that is true of
</div><div id="l1714" class="code_block">all salaries, or rather is the name of a <span class="nb">{</span><span class="k">\em</span> bag<span class="nb">}</span> of all salaries.
</div><div id="l1715" class="code_block">It is a bag since it may contain the same salary multiple times.
</div><div id="l1716" class="code_block"><span class="k">\ourprolog\</span> provides a predicate <span class="k">\verb</span>|bagSum| which can be used to
</div><div id="l1717" class="code_block">sum up the elements in a named bag.  So given the definition of the
</div><div id="l1718" class="code_block">HiLog predicate <span class="k">\verb</span>|salaries/1| above, we can get the sum of all the
</div><div id="l1719" class="code_block">salaries with:
</div><div id="l1720" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1721" class="code_block">    :- bagSum(salaries,TotalSals).
</div><div id="l1722" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1723" class="code_block">The first argument to <span class="k">\verb</span>|bagSum| is the name of a bag, and the
</div><div id="l1724" class="code_block">second is bound to the sum of the elements in the bag.
</div><div id="l1725" class="code_block">
</div><div id="l1726" class="code_block">We can also do a ``group by&#39;&#39; to get total salaries within departments
</div><div id="l1727" class="code_block">as follows.  We define a parameterized predicate, <span class="k">\verb</span>|sals(Dept)|,
</div><div id="l1728" class="code_block">to be the bag of salaries of employees in department <span class="k">\verb</span>|Dept|, as
</div><div id="l1729" class="code_block">follows:
</div><div id="l1730" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1731" class="code_block">    sals(Dept)(Sal) :- employee(<span class="nb">_</span>Name,Dept,Sal).
</div><div id="l1732" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1733" class="code_block">This rule says that <span class="k">\verb</span>|Sal| is in the bag named <span class="k">\verb</span>|sals(Dept)|
</div><div id="l1734" class="code_block">if there is an employee with some name who works in department
</div><div id="l1735" class="code_block"><span class="k">\verb</span>|Dept| and has salary <span class="k">\verb</span>|Sal|.
</div><div id="l1736" class="code_block">
</div><div id="l1737" class="code_block">Now with this definition, we can define a predicate,
</div><div id="l1738" class="code_block"><span class="k">\verb</span>|deptPayroll/2|, that associates with each department the sum of
</div><div id="l1739" class="code_block">all the salaries of employees in that department:
</div><div id="l1740" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1741" class="code_block">    deptPayroll(Dept,Payroll) :- bagSum(sals(Dept),Payroll).
</div><div id="l1742" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1743" class="code_block">
</div><div id="l1744" class="code_block"><span class="k">\ourprolog\</span> provides analogous aggregate operators, described below, to
</div><div id="l1745" class="code_block">compute the minimum, maximum, count, and average, of a bag,
</div><div id="l1746" class="code_block">respectively.  These predicates are all defined using a more basic
</div><div id="l1747" class="code_block">predicate <span class="k">\verb</span>|bagReduce/4|.
</div><div id="l1748" class="code_block">
</div><div id="l1749" class="code_block"><span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l1750" class="code_block">
</div><div id="l1751" class="code_block"><span class="k">\ournewitem</span><span class="nb">{</span>bagReduce(?SetPred,?Arg,+Op,+Id)<span class="nb">}{</span>HiLog,Tabling<span class="nb">}</span>
</div><div id="l1752" class="code_block"><span class="k">\ournewitem</span><span class="nb">{</span>filterReduce(?SetPred,?Arg,+Op,+Id)<span class="nb">}{</span>Tabling<span class="nb">}</span>
</div><div id="l1753" class="code_block"><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> bagReduce/4<span class="nb">}}</span> 
</div><div id="l1754" class="code_block"><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> filterReduce/4<span class="nb">}}</span> 
</div><div id="l1755" class="code_block"><span class="nb">{</span><span class="k">\tt</span> SetPred<span class="nb">}</span> must be a HiLog set specification, i.e., a unary HiLog
</div><div id="l1756" class="code_block">predicate.  <span class="nb">{</span><span class="k">\tt</span> Op<span class="nb">}</span> must be a Hilog operation, i.e., a 3-ary HiLog
</div><div id="l1757" class="code_block">predicate that defines an associative operator.  The predicate must
</div><div id="l1758" class="code_block">define a binary function in which the first two arguments determine
</div><div id="l1759" class="code_block">the third.  <span class="nb">{</span><span class="k">\tt</span> Id<span class="nb">}</span> must be the identity of the operator.  <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1760" class="code_block">bagReduce<span class="nb">}</span> returns with <span class="nb">{</span><span class="k">\tt</span> Arg<span class="nb">}</span> bound to the ``reduce&#39;&#39; of the
</div><div id="l1761" class="code_block">elements of the bag determined by <span class="nb">{</span><span class="k">\tt</span> SetPred<span class="nb">}</span> under the operation
</div><div id="l1762" class="code_block"><span class="nb">{</span><span class="k">\tt</span> Op<span class="nb">}</span>.  I.e., <span class="nb">{</span><span class="k">\tt</span> Arg<span class="nb">}</span> becomes the result of applying the operator
</div><div id="l1763" class="code_block">to all the elements in the bag that unify with <span class="nb">{</span><span class="k">\tt</span> SetPred<span class="nb">}</span>.  See the
</div><div id="l1764" class="code_block"><span class="nb">{</span><span class="k">\tt</span> bagSum<span class="nb">}</span> operator below to see an example of <span class="nb">{</span><span class="k">\tt</span> bagReduce<span class="nb">}</span>&#39;s
</div><div id="l1765" class="code_block">use.
</div><div id="l1766" class="code_block">
</div><div id="l1767" class="code_block"><span class="nb">{</span><span class="k">\tt</span> filterReduce/4<span class="nb">}</span> acts as <span class="nb">{</span><span class="k">\tt</span> bagReduce/4<span class="nb">}</span> with two differences.
</div><div id="l1768" class="code_block">First, it does not depend on HiLog, so that <span class="nb">{</span><span class="k">\tt</span> filterReduce/4<span class="nb">}</span> will
</div><div id="l1769" class="code_block">be more robust especially when XSB&#39;s module system is used.  In
</div><div id="l1770" class="code_block">addition, <span class="nb">{</span><span class="k">\tt</span> filterReduce/4<span class="nb">}</span> aggregates solutions to <span class="nb">{</span><span class="k">\tt</span> Pred<span class="nb">}</span>
</div><div id="l1771" class="code_block">using a variance rather than unification.  An example of the use of
</div><div id="l1772" class="code_block"><span class="nb">{</span><span class="k">\tt</span> filterReduce/4<span class="nb">}</span> is given in Chapter <span class="k">\ref</span><span class="nb">{</span>chap:TablingOverview<span class="nb">}</span>.
</div><div id="l1773" class="code_block">
</div><div id="l1774" class="code_block"><span class="k">\ournewitem</span><span class="nb">{</span>bagPO(?SetPred,?Arg,+Order)<span class="nb">}{</span>HiLog,Tabling<span class="nb">}</span>
</div><div id="l1775" class="code_block"><span class="k">\ournewitem</span><span class="nb">{</span>filterPO(?SetPred,?Arg,+Order)<span class="nb">}{</span>Tabling<span class="nb">}</span>
</div><div id="l1776" class="code_block"><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> bagPO/3<span class="nb">}}</span>
</div><div id="l1777" class="code_block"><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> filterPO/3<span class="nb">}}</span>
</div><div id="l1778" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> SetPred<span class="nb">}</span> must be a HiLog set specification, i.e., a unary
</div><div id="l1779" class="code_block">    HiLog predicate.  <span class="nb">{</span><span class="k">\tt</span> Order<span class="nb">}</span> must be a binary Hilog relation that
</div><div id="l1780" class="code_block">    defines a partial order.  <span class="nb">{</span><span class="k">\tt</span> bagPO<span class="nb">}</span> returns nondeterministically
</div><div id="l1781" class="code_block">    with <span class="nb">{</span><span class="k">\tt</span> Arg<span class="nb">}</span> bound to the maximal elements, under <span class="nb">{</span><span class="k">\tt</span> Order<span class="nb">}</span>, of
</div><div id="l1782" class="code_block">    the bag <span class="nb">{</span><span class="k">\tt</span> SetPred<span class="nb">}</span>.  <span class="nb">{</span><span class="k">\tt</span> bagPO/3<span class="nb">}</span> can be used with <span class="nb">{</span><span class="k">\tt</span> Order<span class="nb">}</span>
</div><div id="l1783" class="code_block">    being subsumption to reduce a set of answers and keep only the most
</div><div id="l1784" class="code_block">    general answers.
</div><div id="l1785" class="code_block">
</div><div id="l1786" class="code_block">    See the <span class="nb">{</span><span class="k">\tt</span> bagMax<span class="nb">}</span> operator below to see an example of <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1787" class="code_block">    bagPO<span class="nb">}</span>&#39;s use.
</div><div id="l1788" class="code_block">
</div><div id="l1789" class="code_block"><span class="nb">{</span><span class="k">\tt</span> filterPO/3<span class="nb">}</span> acts as <span class="nb">{</span><span class="k">\tt</span> bagPO/3<span class="nb">}</span> with the single difference that
</div><div id="l1790" class="code_block">it does not depend on HiLog, so that <span class="nb">{</span><span class="k">\tt</span> filterPO/3<span class="nb">}</span> will be more
</div><div id="l1791" class="code_block">robust especially when XSB&#39;s module system is used.
</div><div id="l1792" class="code_block">
</div><div id="l1793" class="code_block"><span class="k">\ournewitem</span><span class="nb">{</span>filterPO(<span class="k">\#</span>Pred,+Order)<span class="nb">}{</span>Tabling<span class="nb">}</span> <span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span>
</div><div id="l1794" class="code_block">filterPO/2<span class="nb">}}</span> 
</div><div id="l1795" class="code_block">
</div><div id="l1796" class="code_block"><span class="nb">{</span><span class="k">\tt</span> filterPO(<span class="k">\#</span>Pred,+Order)<span class="nb">}</span> succeds only for a solution <span class="s">$</span><span class="nb">Pred</span><span class="nv">\theta</span><span class="s">$</span>
</div><div id="l1797" class="code_block">of <span class="nb">{</span><span class="k">\tt</span> Pred<span class="nb">}</span> for which there is no solution <span class="s">$</span><span class="nb">Pred</span><span class="nv">\eta</span><span class="s">$</span> to <span class="nb">{</span><span class="k">\tt</span> Pred<span class="nb">}</span>
</div><div id="l1798" class="code_block">such that <span class="nb">{</span><span class="k">\tt</span> Order(<span class="s">$</span><span class="nb">Pred</span><span class="nv">\eta</span><span class="s">$</span>,<span class="s">$</span><span class="nb">Pred</span><span class="nv">\theta</span><span class="s">$</span>)<span class="nb">}</span>.
</div><div id="l1799" class="code_block">
</div><div id="l1800" class="code_block">Example:
</div><div id="l1801" class="code_block">
</div><div id="l1802" class="code_block">For the following program
</div><div id="l1803" class="code_block">     <span class="k">\begin</span><span class="nb">{</span>center<span class="nb">}</span>
</div><div id="l1804" class="code_block">     <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1805" class="code_block">     <span class="k">\begin</span><span class="nb">{</span>tabular<span class="nb">}{</span>l<span class="nb">}</span>
</div><div id="l1806" class="code_block">          :- table p/2.	<span class="k">\\</span>
</div><div id="l1807" class="code_block">          b(1,2).       <span class="k">\\</span>
</div><div id="l1808" class="code_block">          p(1,3).       <span class="k">\\</span>
</div><div id="l1809" class="code_block">          b(1,1).       <span class="k">\\</span>
</div><div id="l1810" class="code_block"><span class="k">\\</span>
</div><div id="l1811" class="code_block">	  prefer(b(X,X),b(X,Y)):- X <span class="k">\=</span>= Y. 
</div><div id="l1812" class="code_block">     <span class="k">\end</span><span class="nb">{</span>tabular<span class="nb">}</span>
</div><div id="l1813" class="code_block">     <span class="nb">}</span>
</div><div id="l1814" class="code_block">     <span class="k">\end</span><span class="nb">{</span>center<span class="nb">}</span>
</div><div id="l1815" class="code_block">the query 
</div><div id="l1816" class="code_block"><span class="k">\begin</span><span class="nb">{</span>center<span class="nb">}</span>
</div><div id="l1817" class="code_block"><span class="nb">{</span><span class="k">\tt</span> ?- filterPO(b(X,Y)<span class="nb">}</span>
</div><div id="l1818" class="code_block"><span class="k">\end</span><span class="nb">{</span>center<span class="nb">}</span>
</div><div id="l1819" class="code_block">will succeed only with the binding <span class="nb">{</span><span class="k">\em</span> X = 1,Y = 1<span class="nb">}</span>.
</div><div id="l1820" class="code_block">
</div><div id="l1821" class="code_block"><span class="k">\ournewitem</span><span class="nb">{</span>bagMax(?SetPred,?Arg)<span class="nb">}{</span>HiLog,Tabling<span class="nb">}</span>
</div><div id="l1822" class="code_block"><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> bagMax/2<span class="nb">}}</span>
</div><div id="l1823" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> SetPred<span class="nb">}</span> must be a HiLog set specification, i.e., a unary
</div><div id="l1824" class="code_block">    HiLog predicate.  <span class="nb">{</span><span class="k">\tt</span> bagMax<span class="nb">}</span> returns with <span class="nb">{</span><span class="k">\tt</span> Arg<span class="nb">}</span> bound to the
</div><div id="l1825" class="code_block">    maximum element (under the Prolog term ordering) of the set <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1826" class="code_block">    SetPred<span class="nb">}</span>.  To use this predicate, it must be imported from aggregs,
</div><div id="l1827" class="code_block">    and you must give the following definitions in the main module <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1828" class="code_block">    usermod<span class="nb">}</span>:
</div><div id="l1829" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1830" class="code_block">:- hilog maximum.
</div><div id="l1831" class="code_block">maximum(X,Y,Z) :- X @&lt; Y -&gt; Z=Y ; Z=X.
</div><div id="l1832" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1833" class="code_block">    (These decarations are necessary because of a current limitation in
</div><div id="l1834" class="code_block">    how HiLog predicates can be used.  This requirement will be lifted in
</div><div id="l1835" class="code_block">    a future release.)  With this definition, <span class="nb">{</span><span class="k">\tt</span> bagMax/2<span class="nb">}</span> can be (and
</div><div id="l1836" class="code_block">    is) defined as follows:
</div><div id="l1837" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1838" class="code_block">bagMax(Call,Var) :- bagReduce(Call,Var,maximum,<span class="nb">_</span>).
</div><div id="l1839" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1840" class="code_block">    (Where variables are minimal in the term ordering.)
</div><div id="l1841" class="code_block">
</div><div id="l1842" class="code_block">Another possible definition of <span class="nb">{</span><span class="k">\tt</span> bagMax/2<span class="nb">}</span> would be:
</div><div id="l1843" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1844" class="code_block">:- hilog lt.
</div><div id="l1845" class="code_block">lt(X,Y) :- X @&lt; Y.
</div><div id="l1846" class="code_block">
</div><div id="l1847" class="code_block">bagMax(Call,Var) :- bagPO(Call,Var,lt).
</div><div id="l1848" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1849" class="code_block">This definition would work, but it is slightly less efficient than the
</div><div id="l1850" class="code_block">previous definition since it is known that <span class="nb">{</span><span class="k">\tt</span> bagMax<span class="nb">}</span> is
</div><div id="l1851" class="code_block">deterministic.
</div><div id="l1852" class="code_block">
</div><div id="l1853" class="code_block"><span class="k">\ournewitem</span><span class="nb">{</span>bagMin(?SetPred,?Arg)<span class="nb">}{</span>HiLog,Tabling<span class="nb">}</span>
</div><div id="l1854" class="code_block"><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> bagMin/2<span class="nb">}}</span>
</div><div id="l1855" class="code_block">
</div><div id="l1856" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> SetPred<span class="nb">}</span> must be a HiLog set specification, i.e., a unary
</div><div id="l1857" class="code_block">    HiLog predicate.  <span class="nb">{</span><span class="k">\tt</span> bagMin<span class="nb">}</span> returns with <span class="nb">{</span><span class="k">\tt</span> Arg<span class="nb">}</span> bound to the
</div><div id="l1858" class="code_block">    minimum element (under the Prolog term ordering) of the set <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1859" class="code_block">    SetPred<span class="nb">}</span>.  To use this predicate, it must be imported from aggregs,
</div><div id="l1860" class="code_block">    and you must give the following definitions in the main module <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1861" class="code_block">    usermod<span class="nb">}</span>:
</div><div id="l1862" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1863" class="code_block">:- hilog minimum.  
</div><div id="l1864" class="code_block">minimum(X,Y,Z) :- X @&lt; Y -&gt; Z=X ; Z=Y.
</div><div id="l1865" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1866" class="code_block">    (These decarations are necessary because of a current limitation in
</div><div id="l1867" class="code_block">    how HiLog predicates can be used.  This requirement will be lifted in
</div><div id="l1868" class="code_block">    a future release.)  With this definition, <span class="nb">{</span><span class="k">\tt</span> bagMin/2<span class="nb">}</span> can be (and
</div><div id="l1869" class="code_block">    is) defined as:
</div><div id="l1870" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1871" class="code_block">bagMin(Call,Var) :- bagReduce(Call,Var,minimum,zz(zz)).
</div><div id="l1872" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1873" class="code_block">    (where structures are the largest elements in the term ordering.)
</div><div id="l1874" class="code_block">
</div><div id="l1875" class="code_block"><span class="k">\ournewitem</span><span class="nb">{</span>bagSum(?SetPred,?Arg)<span class="nb">}{</span>HiLog,Tabling<span class="nb">}</span>
</div><div id="l1876" class="code_block"><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> bagSum/2<span class="nb">}}</span>
</div><div id="l1877" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> SetPred<span class="nb">}</span> must be a HiLog set specification, i.e., a unary
</div><div id="l1878" class="code_block">    HiLog predicate.  <span class="nb">{</span><span class="k">\tt</span> bagSum<span class="nb">}</span> returns with <span class="nb">{</span><span class="k">\tt</span> Arg<span class="nb">}</span> bound to the sum
</div><div id="l1879" class="code_block">    of the elements of the set <span class="nb">{</span><span class="k">\tt</span> SetPred<span class="nb">}</span>.  To use this predicate, it
</div><div id="l1880" class="code_block">    must be imported from aggregs, and you must give the following
</div><div id="l1881" class="code_block">    definitions in the main module <span class="nb">{</span><span class="k">\tt</span> usermod<span class="nb">}</span>:
</div><div id="l1882" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1883" class="code_block">:- hilog sum.
</div><div id="l1884" class="code_block">sum(X,Y,Z) :- Z is X+Y.
</div><div id="l1885" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1886" class="code_block">    (These decarations are necessary because of a current limitation in
</div><div id="l1887" class="code_block">    how HiLog predicates can be used.  This requirement will be lifted in
</div><div id="l1888" class="code_block">    a future release.)  With this definition, <span class="nb">{</span><span class="k">\tt</span> bagSum/2<span class="nb">}</span> can be (and
</div><div id="l1889" class="code_block">    is) defined as:
</div><div id="l1890" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1891" class="code_block">bagSum(Call,Var) :- bagReduce(Call,Var,sum,0).
</div><div id="l1892" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1893" class="code_block">
</div><div id="l1894" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>bagCount(?SetPred,?Arg)<span class="nb">}{</span>HiLog,Tabling<span class="nb">}</span>
</div><div id="l1895" class="code_block"><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> bagCount/2<span class="nb">}}</span>
</div><div id="l1896" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> SetPred<span class="nb">}</span> must be a HiLog set specification, i.e., a unary
</div><div id="l1897" class="code_block">    HiLog predicate.  <span class="nb">{</span><span class="k">\tt</span> bagCount<span class="nb">}</span> returns with <span class="nb">{</span><span class="k">\tt</span> Arg<span class="nb">}</span> bound to the
</div><div id="l1898" class="code_block">    count (i.e., number) of elements of the set <span class="nb">{</span><span class="k">\tt</span> SetPred<span class="nb">}</span>.  To use
</div><div id="l1899" class="code_block">    this predicate, it must be imported from aggregs, and you must give
</div><div id="l1900" class="code_block">    the following definitions in the main module <span class="nb">{</span><span class="k">\tt</span> usermod<span class="nb">}</span>:
</div><div id="l1901" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1902" class="code_block">:- hilog successor.
</div><div id="l1903" class="code_block">successor(X,<span class="nb">_</span>Y,Z) :- Z is X+1.
</div><div id="l1904" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1905" class="code_block">    (These decarations are necessary because of a current limitation in
</div><div id="l1906" class="code_block">    how HiLog predicates can be used.  This requirement will be lifted in
</div><div id="l1907" class="code_block">    a future release.)  With this definition, <span class="nb">{</span><span class="k">\tt</span> bagCount/2<span class="nb">}</span> can be (and
</div><div id="l1908" class="code_block">    is) defined as:
</div><div id="l1909" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1910" class="code_block">bagCount(Call,Var) :- bagReduce(Call,Var,successor,0).
</div><div id="l1911" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1912" class="code_block">
</div><div id="l1913" class="code_block"><span class="k">\ournewitem</span><span class="nb">{</span>bagAvg(?SetPred,?Arg)<span class="nb">}{</span>HiLog,Tabling<span class="nb">}</span>
</div><div id="l1914" class="code_block"><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> bagAvg/2<span class="nb">}}</span>
</div><div id="l1915" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> SetPred<span class="nb">}</span> must be a HiLog set specification, i.e., a unary
</div><div id="l1916" class="code_block">    HiLog predicate.  <span class="nb">{</span><span class="k">\tt</span> bagAvg<span class="nb">}</span> returns with <span class="nb">{</span><span class="k">\tt</span> Arg<span class="nb">}</span> bound to the
</div><div id="l1917" class="code_block">    average (i.e., mean) of elements of the set <span class="nb">{</span><span class="k">\tt</span> SetPred<span class="nb">}</span>.  To use
</div><div id="l1918" class="code_block">    this predicate, it must be imported from aggregs, and you must give
</div><div id="l1919" class="code_block">    the following definitions in the main module <span class="nb">{</span><span class="k">\tt</span> usermod<span class="nb">}</span>:
</div><div id="l1920" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1921" class="code_block">:- hilog sumcount.
</div><div id="l1922" class="code_block">sumcount([S|C],X,[S1|C1]) :- S1 is S+X, C1 is C+1.
</div><div id="l1923" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1924" class="code_block">    (These decarations are necessary because of a current limitation in
</div><div id="l1925" class="code_block">    how HiLog predicates can be used.  This requirement will be lifted in
</div><div id="l1926" class="code_block">    a future release.)  With this definition, <span class="nb">{</span><span class="k">\tt</span> bagAvg/2<span class="nb">}</span> can be (and
</div><div id="l1927" class="code_block">    is) defined as:
</div><div id="l1928" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1929" class="code_block">bagAvg(Call,Avg) :- 
</div><div id="l1930" class="code_block">    bagReduce(Call,[Sum|Count],sumcount,[0|0]),
</div><div id="l1931" class="code_block">    Avg is Sum/Count.
</div><div id="l1932" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1933" class="code_block">
</div><div id="l1934" class="code_block"><span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l1935" class="code_block">
</div><div id="l1936" class="code_block"><span class="c">%-------------------------------------------------------------------------</span>
</div><div id="l1937" class="code_block"><span class="k">\section</span><span class="nb">{</span>Comparison<span class="nb">}</span> <span class="k">\label</span><span class="nb">{</span>Comparison<span class="nb">}</span>
</div><div id="l1938" class="code_block"><span class="k">\input</span><span class="nb">{</span>comparison<span class="nb">}</span>
</div><div id="l1939" class="code_block"><span class="c">%-------------------------------------------------------------------------</span>
</div><div id="l1940" class="code_block">
</div><div id="l1941" class="code_block"><span class="k">\section</span><span class="nb">{</span>Meta-Predicates<span class="nb">}</span> <span class="k">\label</span><span class="nb">{</span>meta<span class="nb">_</span>predicates<span class="nb">}</span>
</div><div id="l1942" class="code_block"><span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l1943" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>call(<span class="k">\#</span>X)<span class="nb">}</span><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> call/1<span class="nb">}}</span> 
</div><div id="l1944" class="code_block"><span class="c">%\predindex{call/1~(P)}</span>
</div><div id="l1945" class="code_block">    If <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> is a nonvariable term in the program text, then it is 
</div><div id="l1946" class="code_block">    executed exactly as if <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> appeared in the program text instead 
</div><div id="l1947" class="code_block">    of <span class="nb">{</span><span class="k">\tt</span> call(X)<span class="nb">}</span>,
</div><div id="l1948" class="code_block">    e.g.
</div><div id="l1949" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>center<span class="nb">}</span>
</div><div id="l1950" class="code_block">        <span class="nb">{</span><span class="k">\tt</span> <span class="s">$</span><span class="nv">\ldots</span><span class="s">$</span>, p(a), call( (q(X), r(Y)) ), s(X), <span class="s">$</span><span class="nv">\ldots</span><span class="s">$</span><span class="nb">}</span>
</div><div id="l1951" class="code_block">    <span class="k">\end</span><span class="nb">{</span>center<span class="nb">}</span>
</div><div id="l1952" class="code_block">    is equivalent to
</div><div id="l1953" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>center<span class="nb">}</span>
</div><div id="l1954" class="code_block">        <span class="nb">{</span><span class="k">\tt</span> <span class="s">$</span><span class="nv">\ldots</span><span class="s">$</span>, p(a), q(X), r(Y), s(X), <span class="s">$</span><span class="nv">\ldots</span><span class="s">$</span><span class="nb">}</span>
</div><div id="l1955" class="code_block">    <span class="k">\end</span><span class="nb">{</span>center<span class="nb">}</span>
</div><div id="l1956" class="code_block">    However, if <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> is a variable in the program text,
</div><div id="l1957" class="code_block">    then if at runtime <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> is instantiated to a term which 
</div><div id="l1958" class="code_block">    would be acceptable as the body of a clause, the goal 
</div><div id="l1959" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> call(X)<span class="nb">}</span> is executed as if that
</div><div id="l1960" class="code_block">    term appeared textually in place of the <span class="nb">{</span><span class="k">\tt</span> call(X)<span class="nb">}</span>,
</div><div id="l1961" class="code_block">    <span class="nb">{</span><span class="k">\em</span> except that<span class="nb">}</span> any cut (`!&#39;)<span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> &quot;!/0<span class="nb">}}</span><span class="k">\index</span><span class="nb">{</span>cut<span class="nb">}</span>
</div><div id="l1962" class="code_block">    occurring in <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> will remove only those choice points in~<span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span>.
</div><div id="l1963" class="code_block">    If~<span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> is not instantiated as described above,
</div><div id="l1964" class="code_block">    an error message is printed and <span class="nb">{</span><span class="k">\tt</span> call/1<span class="nb">}</span> fails.
</div><div id="l1965" class="code_block">
</div><div id="l1966" class="code_block">    Exceptions:
</div><div id="l1967" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l1968" class="code_block">    <span class="k">\item</span><span class="na">[{\tt instantiation\_error}]</span>
</div><div id="l1969" class="code_block">	Argument 1 of <span class="nb">{</span><span class="k">\tt</span> call/1<span class="nb">}</span> is not instantiated.
</div><div id="l1970" class="code_block">     <span class="k">\item</span><span class="na">[{\tt type\_error}]</span>
</div><div id="l1971" class="code_block">	Argument 1 of <span class="nb">{</span><span class="k">\tt</span> call/1<span class="nb">}</span> is not a callable term.
</div><div id="l1972" class="code_block">    <span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l1973" class="code_block">
</div><div id="l1974" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span><span class="k">\#</span>X<span class="nb">}</span>					      
</div><div id="l1975" class="code_block">    (where <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> is a variable) executes exactly the same as 
</div><div id="l1976" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> call(X)<span class="nb">}</span>.
</div><div id="l1977" class="code_block">    However, the explicit use of <span class="nb">{</span><span class="k">\tt</span> call/1<span class="nb">}</span> is considered better
</div><div id="l1978" class="code_block">    programming practice.  The use of a top level variable subgoal
</div><div id="l1979" class="code_block">    elicits a warning from the compiler.
</div><div id="l1980" class="code_block">
</div><div id="l1981" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>once(<span class="k">\#</span>X)<span class="nb">}</span>
</div><div id="l1982" class="code_block"><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> once/1<span class="nb">}}</span> 
</div><div id="l1983" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> once/1<span class="nb">}</span> is defined as <span class="nb">{</span><span class="k">\tt</span> once(X):- call(X),!.<span class="nb">}</span>  <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1984" class="code_block">    once/1<span class="nb">}</span> should be used with care in tabled programs.  The compiler
</div><div id="l1985" class="code_block">    can not determine whether a tabled predicate is called in the
</div><div id="l1986" class="code_block">    scope of <span class="nb">{</span><span class="k">\tt</span> once/1<span class="nb">}</span>, and such a call may lead to runtime errors.
</div><div id="l1987" class="code_block">    If a tabled predicate may occur in the scope of <span class="nb">{</span><span class="k">\tt</span> once/1<span class="nb">}</span>, use
</div><div id="l1988" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> table<span class="k">\_once</span>/1<span class="nb">}</span> instead.
</div><div id="l1989" class="code_block">
</div><div id="l1990" class="code_block">    Exceptions: The same as <span class="nb">{</span><span class="k">\tt</span> call/1<span class="nb">}</span>.
</div><div id="l1991" class="code_block">
</div><div id="l1992" class="code_block"><span class="k">\ouritem</span><span class="nb">{</span>table<span class="k">\_once</span>(<span class="k">\#</span>X)<span class="nb">}</span>
</div><div id="l1993" class="code_block"><span class="k">\index</span><span class="nb">{{</span><span class="k">\tt</span> table<span class="k">\_once</span>/1<span class="nb">}}</span> 
</div><div id="l1994" class="code_block">    <span class="nb">{</span><span class="k">\tt</span> table<span class="k">\_once</span>/1<span class="nb">}</span> is a weaker form of <span class="nb">{</span><span class="k">\tt</span> once/1<span class="nb">}</span>, suitable for
</div><div id="l1995" class="code_block">    situations in which a single solution is desired for a
</div><div id="l1996" class="code_block">    subcomputation that may involve a call to a tabled predicate.  <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1997" class="code_block">    table<span class="k">\_once</span>(?Pred)<span class="nb">}</span> succeeds only once even if there are many
</div><div id="l1998" class="code_block">    solutions to the subgoal <span class="nb">{</span><span class="k">\tt</span> Pred<span class="nb">}</span>.  However, it does not ``cut
</div><div id="l1999" class="code_block">    over&#39;&#39; the subcomputation started by the subgoal <span class="nb">{</span><span class="k">\tt</span> Pred<span class="nb">}</span>,
</div><div id="l2000" class="code_block">    thereby ensuring the correct evaluation of tabled subgoals.
</div><div id="l2001" class="code_block">
</div><div id="l2002" class="code_block"><span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l2003" class="code_block">
</div><div id="l2004" class="code_block">
</div><div id="l2005" class="code_block"><span class="c">%%% Local Variables: </span>
</div><div id="l2006" class="code_block"><span class="c">%%% mode: latex</span>
</div><div id="l2007" class="code_block"><span class="c">%%% TeX-master: &quot;manual1&quot;</span>
</div><div id="l2008" class="code_block"><span class="c">%%% End: </span>
</div></pre></div></td></tr></table></div>

      
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