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<span class="normal"> 682</span>
<span class="normal"> 683</span>
<span class="normal"> 684</span>
<span class="normal"> 685</span>
<span class="normal"> 686</span>
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<span class="normal"> 688</span>
<span class="normal"> 689</span>
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<span class="normal"> 699</span>
<span class="normal"> 700</span>
<span class="normal"> 701</span>
<span class="normal"> 702</span>
<span class="normal"> 703</span>
<span class="normal"> 704</span>
<span class="normal"> 705</span>
<span class="normal"> 706</span>
<span class="normal"> 707</span>
<span class="normal"> 708</span>
<span class="normal"> 709</span>
<span class="normal"> 710</span>
<span class="normal"> 711</span>
<span class="normal"> 712</span>
<span class="normal"> 713</span>
<span class="normal"> 714</span>
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<span class="normal"> 720</span>
<span class="normal"> 721</span>
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<span class="normal"> 723</span>
<span class="normal"> 724</span>
<span class="normal"> 725</span>
<span class="normal"> 726</span>
<span class="normal"> 727</span>
<span class="normal"> 728</span>
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<span class="normal"> 731</span>
<span class="normal"> 732</span>
<span class="normal"> 733</span>
<span class="normal"> 734</span>
<span class="normal"> 735</span>
<span class="normal"> 736</span>
<span class="normal"> 737</span>
<span class="normal"> 738</span>
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<span class="normal"> 740</span>
<span class="normal"> 741</span>
<span class="normal"> 742</span>
<span class="normal"> 743</span>
<span class="normal"> 744</span>
<span class="normal"> 745</span>
<span class="normal"> 746</span>
<span class="normal"> 747</span>
<span class="normal"> 748</span>
<span class="normal"> 749</span>
<span class="normal"> 750</span>
<span class="normal"> 751</span>
<span class="normal"> 752</span>
<span class="normal"> 753</span>
<span class="normal"> 754</span>
<span class="normal"> 755</span>
<span class="normal"> 756</span>
<span class="normal"> 757</span>
<span class="normal"> 758</span>
<span class="normal"> 759</span>
<span class="normal"> 760</span>
<span class="normal"> 761</span>
<span class="normal"> 762</span>
<span class="normal"> 763</span>
<span class="normal"> 764</span>
<span class="normal"> 765</span>
<span class="normal"> 766</span>
<span class="normal"> 767</span>
<span class="normal"> 768</span>
<span class="normal"> 769</span>
<span class="normal"> 770</span>
<span class="normal"> 771</span>
<span class="normal"> 772</span>
<span class="normal"> 773</span>
<span class="normal"> 774</span>
<span class="normal"> 775</span>
<span class="normal"> 776</span>
<span class="normal"> 777</span>
<span class="normal"> 778</span>
<span class="normal"> 779</span>
<span class="normal"> 780</span>
<span class="normal"> 781</span>
<span class="normal"> 782</span>
<span class="normal"> 783</span>
<span class="normal"> 784</span>
<span class="normal"> 785</span>
<span class="normal"> 786</span>
<span class="normal"> 787</span>
<span class="normal"> 788</span>
<span class="normal"> 789</span>
<span class="normal"> 790</span>
<span class="normal"> 791</span>
<span class="normal"> 792</span>
<span class="normal"> 793</span>
<span class="normal"> 794</span>
<span class="normal"> 795</span>
<span class="normal"> 796</span>
<span class="normal"> 797</span>
<span class="normal"> 798</span>
<span class="normal"> 799</span>
<span class="normal"> 800</span>
<span class="normal"> 801</span>
<span class="normal"> 802</span>
<span class="normal"> 803</span>
<span class="normal"> 804</span>
<span class="normal"> 805</span>
<span class="normal"> 806</span>
<span class="normal"> 807</span>
<span class="normal"> 808</span>
<span class="normal"> 809</span>
<span class="normal"> 810</span>
<span class="normal"> 811</span>
<span class="normal"> 812</span>
<span class="normal"> 813</span>
<span class="normal"> 814</span>
<span class="normal"> 815</span>
<span class="normal"> 816</span>
<span class="normal"> 817</span>
<span class="normal"> 818</span>
<span class="normal"> 819</span>
<span class="normal"> 820</span>
<span class="normal"> 821</span>
<span class="normal"> 822</span>
<span class="normal"> 823</span>
<span class="normal"> 824</span>
<span class="normal"> 825</span>
<span class="normal"> 826</span>
<span class="normal"> 827</span>
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<span class="normal"> 829</span>
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<span class="normal"> 831</span>
<span class="normal"> 832</span>
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<span class="normal"> 839</span>
<span class="normal"> 840</span>
<span class="normal"> 841</span>
<span class="normal"> 842</span>
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<span class="normal"> 850</span>
<span class="normal"> 851</span>
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<span class="normal"> 864</span>
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<span class="normal"> 868</span>
<span class="normal"> 869</span>
<span class="normal"> 870</span>
<span class="normal"> 871</span>
<span class="normal"> 872</span>
<span class="normal"> 873</span>
<span class="normal"> 874</span>
<span class="normal"> 875</span>
<span class="normal"> 876</span>
<span class="normal"> 877</span>
<span class="normal"> 878</span>
<span class="normal"> 879</span>
<span class="normal"> 880</span>
<span class="normal"> 881</span>
<span class="normal"> 882</span>
<span class="normal"> 883</span>
<span class="normal"> 884</span>
<span class="normal"> 885</span>
<span class="normal"> 886</span>
<span class="normal"> 887</span>
<span class="normal"> 888</span>
<span class="normal"> 889</span>
<span class="normal"> 890</span>
<span class="normal"> 891</span>
<span class="normal"> 892</span>
<span class="normal"> 893</span>
<span class="normal"> 894</span>
<span class="normal"> 895</span>
<span class="normal"> 896</span>
<span class="normal"> 897</span>
<span class="normal"> 898</span>
<span class="normal"> 899</span>
<span class="normal"> 900</span>
<span class="normal"> 901</span>
<span class="normal"> 902</span>
<span class="normal"> 903</span>
<span class="normal"> 904</span>
<span class="normal"> 905</span>
<span class="normal"> 906</span>
<span class="normal"> 907</span>
<span class="normal"> 908</span>
<span class="normal"> 909</span>
<span class="normal"> 910</span>
<span class="normal"> 911</span>
<span class="normal"> 912</span>
<span class="normal"> 913</span>
<span class="normal"> 914</span>
<span class="normal"> 915</span>
<span class="normal"> 916</span>
<span class="normal"> 917</span>
<span class="normal"> 918</span>
<span class="normal"> 919</span>
<span class="normal"> 920</span>
<span class="normal"> 921</span>
<span class="normal"> 922</span>
<span class="normal"> 923</span>
<span class="normal"> 924</span>
<span class="normal"> 925</span>
<span class="normal"> 926</span>
<span class="normal"> 927</span>
<span class="normal"> 928</span>
<span class="normal"> 929</span>
<span class="normal"> 930</span>
<span class="normal"> 931</span>
<span class="normal"> 932</span>
<span class="normal"> 933</span>
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<span class="normal"> 935</span>
<span class="normal"> 936</span>
<span class="normal"> 937</span>
<span class="normal"> 938</span>
<span class="normal"> 939</span>
<span class="normal"> 940</span>
<span class="normal"> 941</span>
<span class="normal"> 942</span>
<span class="normal"> 943</span>
<span class="normal"> 944</span>
<span class="normal"> 945</span>
<span class="normal"> 946</span>
<span class="normal"> 947</span>
<span class="normal"> 948</span>
<span class="normal"> 949</span>
<span class="normal"> 950</span>
<span class="normal"> 951</span>
<span class="normal"> 952</span>
<span class="normal"> 953</span>
<span class="normal"> 954</span>
<span class="normal"> 955</span>
<span class="normal"> 956</span>
<span class="normal"> 957</span>
<span class="normal"> 958</span>
<span class="normal"> 959</span>
<span class="normal"> 960</span>
<span class="normal"> 961</span>
<span class="normal"> 962</span>
<span class="normal"> 963</span>
<span class="normal"> 964</span>
<span class="normal"> 965</span>
<span class="normal"> 966</span>
<span class="normal"> 967</span>
<span class="normal"> 968</span>
<span class="normal"> 969</span>
<span class="normal"> 970</span>
<span class="normal"> 971</span>
<span class="normal"> 972</span>
<span class="normal"> 973</span>
<span class="normal"> 974</span>
<span class="normal"> 975</span>
<span class="normal"> 976</span>
<span class="normal"> 977</span>
<span class="normal"> 978</span>
<span class="normal"> 979</span>
<span class="normal"> 980</span>
<span class="normal"> 981</span>
<span class="normal"> 982</span>
<span class="normal"> 983</span>
<span class="normal"> 984</span>
<span class="normal"> 985</span>
<span class="normal"> 986</span>
<span class="normal"> 987</span>
<span class="normal"> 988</span>
<span class="normal"> 989</span>
<span class="normal"> 990</span>
<span class="normal"> 991</span>
<span class="normal"> 992</span>
<span class="normal"> 993</span>
<span class="normal"> 994</span>
<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>
<span class="normal">1047</span>
<span class="normal">1048</span>
<span class="normal">1049</span>
<span class="normal">1050</span>
<span class="normal">1051</span>
<span class="normal">1052</span>
<span class="normal">1053</span>
<span class="normal">1054</span>
<span class="normal">1055</span>
<span class="normal">1056</span>
<span class="normal">1057</span>
<span class="normal">1058</span>
<span class="normal">1059</span>
<span class="normal">1060</span>
<span class="normal">1061</span>
<span class="normal">1062</span>
<span class="normal">1063</span>
<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>
<span class="normal">1137</span>
<span class="normal">1138</span>
<span class="normal">1139</span>
<span class="normal">1140</span>
<span class="normal">1141</span>
<span class="normal">1142</span>
<span class="normal">1143</span>
<span class="normal">1144</span>
<span class="normal">1145</span>
<span class="normal">1146</span>
<span class="normal">1147</span>
<span class="normal">1148</span>
<span class="normal">1149</span>
<span class="normal">1150</span>
<span class="normal">1151</span>
<span class="normal">1152</span>
<span class="normal">1153</span>
<span class="normal">1154</span>
<span class="normal">1155</span>
<span class="normal">1156</span>
<span class="normal">1157</span>
<span class="normal">1158</span>
<span class="normal">1159</span>
<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>
<span class="normal">1212</span>
<span class="normal">1213</span>
<span class="normal">1214</span>
<span class="normal">1215</span>
<span class="normal">1216</span>
<span class="normal">1217</span>
<span class="normal">1218</span>
<span class="normal">1219</span>
<span class="normal">1220</span>
<span class="normal">1221</span>
<span class="normal">1222</span>
<span class="normal">1223</span>
<span class="normal">1224</span>
<span class="normal">1225</span>
<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>
<span class="normal">1243</span>
<span class="normal">1244</span>
<span class="normal">1245</span>
<span class="normal">1246</span>
<span class="normal">1247</span>
<span class="normal">1248</span>
<span class="normal">1249</span>
<span class="normal">1250</span>
<span class="normal">1251</span>
<span class="normal">1252</span>
<span class="normal">1253</span>
<span class="normal">1254</span>
<span class="normal">1255</span>
<span class="normal">1256</span>
<span class="normal">1257</span>
<span class="normal">1258</span>
<span class="normal">1259</span>
<span class="normal">1260</span>
<span class="normal">1261</span>
<span class="normal">1262</span>
<span class="normal">1263</span>
<span class="normal">1264</span>
<span class="normal">1265</span>
<span class="normal">1266</span>
<span class="normal">1267</span>
<span class="normal">1268</span>
<span class="normal">1269</span>
<span class="normal">1270</span>
<span class="normal">1271</span>
<span class="normal">1272</span>
<span class="normal">1273</span>
<span class="normal">1274</span>
<span class="normal">1275</span>
<span class="normal">1276</span>
<span class="normal">1277</span>
<span class="normal">1278</span>
<span class="normal">1279</span>
<span class="normal">1280</span>
<span class="normal">1281</span>
<span class="normal">1282</span>
<span class="normal">1283</span>
<span class="normal">1284</span>
<span class="normal">1285</span>
<span class="normal">1286</span>
<span class="normal">1287</span>
<span class="normal">1288</span>
<span class="normal">1289</span>
<span class="normal">1290</span>
<span class="normal">1291</span>
<span class="normal">1292</span>
<span class="normal">1293</span>
<span class="normal">1294</span>
<span class="normal">1295</span>
<span class="normal">1296</span>
<span class="normal">1297</span>
<span class="normal">1298</span>
<span class="normal">1299</span>
<span class="normal">1300</span>
<span class="normal">1301</span>
<span class="normal">1302</span>
<span class="normal">1303</span>
<span class="normal">1304</span>
<span class="normal">1305</span>
<span class="normal">1306</span>
<span class="normal">1307</span>
<span class="normal">1308</span>
<span class="normal">1309</span>
<span class="normal">1310</span>
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<span class="normal">1942</span>
<span class="normal">1943</span>
<span class="normal">1944</span>
<span class="normal">1945</span>
<span class="normal">1946</span>
<span class="normal">1947</span>
<span class="normal">1948</span>
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<span class="normal">1980</span>
<span class="normal">1981</span>
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<span class="normal">1984</span>
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<span class="normal">1990</span>
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<span class="normal">1998</span>
<span class="normal">1999</span>
<span class="normal">2000</span>
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<span class="normal">2009</span>
<span class="normal">2010</span>
<span class="normal">2011</span>
<span class="normal">2012</span>
<span class="normal">2013</span>
<span class="normal">2014</span>
<span class="normal">2015</span>
<span class="normal">2016</span>
<span class="normal">2017</span>
<span class="normal">2018</span>
<span class="normal">2019</span>
<span class="normal">2020</span>
<span class="normal">2021</span>
<span class="normal">2022</span>
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<span class="normal">2078</span></pre></div></td><td class="code"><div><pre><div id="l1" class="code_block"><span class="c">%========================================================</span>
</div><div id="l2" class="code_block">
</div><div id="l3" class="code_block"><span class="k">\newcommand</span><span class="nb">{</span><span class="k">\retn</span><span class="nb">}{</span><span class="k">\code</span><span class="nb">{</span>ret/n<span class="nb">}}</span>
</div><div id="l4" class="code_block">
</div><div id="l5" class="code_block"><span class="c">%--------------------------------------------------------------------------</span>
</div><div id="l6" class="code_block">
</div><div id="l7" class="code_block"><span class="k">\section</span><span class="nb">{</span>Tabling Declarations and Builtins<span class="nb">}</span> <span class="k">\label</span><span class="nb">{</span>sec:TablingPredicates<span class="nb">}</span>
</div><div id="l8" class="code_block">
</div><div id="l9" class="code_block">In XSB, tables are designed so that they can be used transparently by
</div><div id="l10" class="code_block">computations.  However, it is necessary to first inform the system of
</div><div id="l11" class="code_block">which predicates should be evaluated using tabled resolution
</div><div id="l12" class="code_block">(<span class="k">\refsec</span><span class="nb">{</span>sec:CompilerOptions<span class="nb">}</span>), and whether variant or subsumptive
</div><div id="l13" class="code_block">tabling should be used (<span class="k">\refchap</span><span class="nb">{</span>chap:TablingOverview<span class="nb">}</span>).  Further, it
</div><div id="l14" class="code_block">is often useful to be able to explicitly inspect a table, or to alter
</div><div id="l15" class="code_block">its state.  The predicates described in this section are provided for
</div><div id="l16" class="code_block">these purposes.  In order to ground the discussion of these
</div><div id="l17" class="code_block">predicates, we continue our overview of tables and table creation from
</div><div id="l18" class="code_block"><span class="k">\refchap</span><span class="nb">{</span>chap:TablingOverview<span class="nb">}</span>.  For a detailed description of the
</div><div id="l19" class="code_block">implementation of table access routines in XSB, the reader is referred
</div><div id="l20" class="code_block">to~<span class="k">\cite</span><span class="nb">{</span>RRSSW98,TST99,CuSW99b<span class="nb">}</span> and other papers listed in the
</div><div id="l21" class="code_block">bibliography.
</div><div id="l22" class="code_block">
</div><div id="l23" class="code_block"><span class="c">% - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
</div><div id="l24" class="code_block">
</div><div id="l25" class="code_block"><span class="k">\subsubsection*</span><span class="nb">{</span>Tables and Table Entries<span class="nb">}</span>
</div><div id="l26" class="code_block">
</div><div id="l27" class="code_block">Abstractly, a table can be seen as a set of entry triples <span class="s">$</span><span class="nv">\langle</span>
</div><div id="l28" class="code_block"><span class="nb">S,</span><span class="nv">\cA</span><span class="nb">,Status </span><span class="nv">\rangle</span><span class="s">$</span> where <span class="s">$</span><span class="nb">S</span><span class="s">$</span> is a subgoal, <span class="s">$</span><span class="nv">\cA</span><span class="s">$</span> is its associated
</div><div id="l29" class="code_block">answer set, and <span class="s">$</span><span class="nb">Status</span><span class="s">$</span> its status~---~whether it is
</div><div id="l30" class="code_block"><span class="k">\texttt</span><span class="nb">{</span>complete<span class="nb">}</span> or <span class="k">\texttt</span><span class="nb">{</span>incomplete<span class="nb">}</span>.  In terms of implementation,
</div><div id="l31" class="code_block">``the table&#39;&#39; is actually a set of mini-tables, each one containing
</div><div id="l32" class="code_block">entries for a particular predicate.  Hence, we may refer to the table
</div><div id="l33" class="code_block">containing entries for some predicate <span class="k">\code</span><span class="nb">{</span>p/n<span class="nb">}</span> as ``the table for
</div><div id="l34" class="code_block"><span class="k">\code</span><span class="nb">{</span>p/n<span class="nb">}</span>.&#39;&#39;  Further recall that a particular predicate may be
</div><div id="l35" class="code_block">evaluated according to either a variant or subsumptive strategy as
</div><div id="l36" class="code_block">chosen by the user.  Invocation of a call during an evaluation leads
</div><div id="l37" class="code_block">to the classification of the call, as well as its possible insertion
</div><div id="l38" class="code_block">into the table.  Each call can be classified as either (a) a
</div><div id="l39" class="code_block"><span class="k">\emph</span><span class="nb">{</span>generator<span class="nb">}</span>, or <span class="k">\emph</span><span class="nb">{</span>producer<span class="nb">}</span>, of an answer set, or (b) a
</div><div id="l40" class="code_block"><span class="k">\emph</span><span class="nb">{</span>consumer<span class="nb">}</span> of the answer set of some subgoal in the table.
</div><div id="l41" class="code_block">Creation of a table entry thus relies not only on the call and on the
</div><div id="l42" class="code_block">subgoals already present in the table, but also upon whether
</div><div id="l43" class="code_block">call-variance or call-subsumption is used (cf. <span class="k">\cite</span><span class="nb">{</span>TST99<span class="nb">}</span>).
</div><div id="l44" class="code_block">
</div><div id="l45" class="code_block"><span class="c">% - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
</div><div id="l46" class="code_block">
</div><div id="l47" class="code_block"><span class="k">\subsubsection*</span><span class="nb">{</span>Answers, Returns, and Templates<span class="nb">}</span>
</div><div id="l48" class="code_block">
</div><div id="l49" class="code_block"><span class="k">\index</span><span class="nb">{</span>answer substitution<span class="nb">}</span>
</div><div id="l50" class="code_block"><span class="k">\index</span><span class="nb">{</span>substitution factor<span class="nb">}</span>
</div><div id="l51" class="code_block"><span class="c">%</span>
</div><div id="l52" class="code_block">Given a table entry <span class="s">$</span><span class="o">(</span><span class="nb">S,</span><span class="nv">\cA</span><span class="nb">,Status</span><span class="o">)</span><span class="s">$</span>, the set of variables in <span class="s">$</span><span class="nb">S</span><span class="s">$</span> is
</div><div id="l53" class="code_block">sometimes called the <span class="nb">{</span><span class="k">\em</span> substitution factor<span class="nb">}</span> of <span class="s">$</span><span class="nb">S</span><span class="s">$</span>.  The order of
</div><div id="l54" class="code_block">arguments in the substitution factor corresponds to the order of
</div><div id="l55" class="code_block">distinct variables in a left-to-right traversal of <span class="s">$</span><span class="nb">S</span><span class="s">$</span>.  Each answer
</div><div id="l56" class="code_block">in <span class="s">$</span><span class="nv">\cA</span><span class="s">$</span> substitutes values for the variables in the substitution
</div><div id="l57" class="code_block">factor of <span class="s">$</span><span class="nb">S</span><span class="s">$</span>; this substitution is sometimes called an answer
</div><div id="l58" class="code_block">substitution.  The table inspection predicates allow access to
</div><div id="l59" class="code_block">substitution factors and answer substitutions through a family of terms
</div><div id="l60" class="code_block">whose principle functors are <span class="k">\retn</span>, where <span class="k">\code</span><span class="nb">{</span>n<span class="nb">}</span> is the size of the
</div><div id="l61" class="code_block">substitution factor.
</div><div id="l62" class="code_block">
</div><div id="l63" class="code_block"><span class="k">\begin</span><span class="nb">{</span>example<span class="nb">}</span>
</div><div id="l64" class="code_block">Let <span class="s">$</span><span class="nb">S </span><span class="o">=</span><span class="s">$</span> <span class="k">\code</span><span class="nb">{</span>p(X,f(Y))<span class="nb">}</span> be a producer subgoal (or simply, a subgoal
</div><div id="l65" class="code_block">if call-variance is used).  Using the <span class="k">\retn</span> notation, the substitution
</div><div id="l66" class="code_block">factor can be depicted as <span class="k">\code</span><span class="nb">{</span>ret(X,Y)<span class="nb">}</span>, while the answer
</div><div id="l67" class="code_block">substitution <span class="k">\code</span><span class="nb">{</span><span class="k">\{</span>X=a,Y=b<span class="k">\}</span><span class="nb">}</span> is depicted as <span class="k">\code</span><span class="nb">{</span>ret(a,b)<span class="nb">}</span>.  Note
</div><div id="l68" class="code_block">that the application of the answer substitution to the producer
</div><div id="l69" class="code_block">subgoal yields the answer <span class="k">\code</span><span class="nb">{</span>p(a,f(b))<span class="nb">}</span>.
</div><div id="l70" class="code_block">
</div><div id="l71" class="code_block">To take a slightly more complex example, consider the subgoal
</div><div id="l72" class="code_block"><span class="k">\code</span><span class="nb">{</span>q(X)<span class="nb">}</span> where <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> is an attributed variable whose attribute is
</div><div id="l73" class="code_block"><span class="k">\code</span><span class="nb">{</span>f(Z,Y,Y)<span class="nb">}</span>.  In this case the substitution factor is
</div><div id="l74" class="code_block"><span class="k">\code</span><span class="nb">{</span>ret(X,Z,Y)<span class="nb">}</span>.<span class="k">\fillBox</span>
</div><div id="l75" class="code_block"><span class="k">\end</span><span class="nb">{</span>example<span class="nb">}</span>
</div><div id="l76" class="code_block">
</div><div id="l77" class="code_block">In a similar manner, XSB maintains substitutions between producer
</div><div id="l78" class="code_block">subgoals and consuming subgoals when subsumption-based tabling is
</div><div id="l79" class="code_block">used.  The <span class="k">\emph</span><span class="nb">{</span>return template<span class="nb">}</span> for a consuming call is a
</div><div id="l80" class="code_block">substitution mapping variables of its producer to subterms of the
</div><div id="l81" class="code_block">call.  This template can then be used to select returns from the
</div><div id="l82" class="code_block">producer which satisfy the consuming call.  Note, then, that a return
</div><div id="l83" class="code_block">template of a <span class="k">\emph</span><span class="nb">{</span>subsumed<span class="nb">}</span> subgoal may show partial instantiations.
</div><div id="l84" class="code_block">Return templates are also represented as <span class="k">\retn</span><span class="nb">{}</span> terms in the manner
</div><div id="l85" class="code_block">described above.
</div><div id="l86" class="code_block">
</div><div id="l87" class="code_block"><span class="k">\begin</span><span class="nb">{</span>example<span class="nb">}</span>
</div><div id="l88" class="code_block">Let <span class="k">\code</span><span class="nb">{</span>p/2<span class="nb">}</span> of the previous example be evaluated using subsumption
</div><div id="l89" class="code_block">and let <span class="s">$</span><span class="nb">S</span><span class="s">$</span> be present in its table.  Further, let <span class="s">$</span><span class="nb">S_</span><span class="m">1</span><span class="s">$</span>:
</div><div id="l90" class="code_block"><span class="k">\code</span><span class="nb">{</span>p(A,f(B))<span class="nb">}</span> and <span class="s">$</span><span class="nb">S_</span><span class="m">2</span><span class="s">$</span>: <span class="k">\code</span><span class="nb">{</span>p(g(Z),f(b))<span class="nb">}</span> be two consuming
</div><div id="l91" class="code_block">subgoals of <span class="s">$</span><span class="nb">S</span><span class="s">$</span><span class="k">\@</span>.  Then the <span class="k">\emph</span><span class="nb">{</span>return template<span class="nb">}</span> of <span class="s">$</span><span class="nb">S_</span><span class="m">1</span><span class="s">$</span> is
</div><div id="l92" class="code_block"><span class="k">\code</span><span class="nb">{</span>ret(A,B)<span class="nb">}</span> and that of <span class="s">$</span><span class="nb">S_</span><span class="m">2</span><span class="s">$</span> is <span class="k">\code</span><span class="nb">{</span>ret(g(Z),b)<span class="nb">}</span>.  <span class="s">$</span><span class="nb">S_</span><span class="m">1</span><span class="s">$</span>, being
</div><div id="l93" class="code_block">a variant of <span class="s">$</span><span class="nb">S</span><span class="s">$</span>, selects all returns of <span class="s">$</span><span class="nb">S</span><span class="s">$</span> such that
</div><div id="l94" class="code_block"><span class="k">\code</span><span class="nb">{</span><span class="k">\{</span>X=A,Y=B<span class="k">\}</span><span class="nb">}</span><span class="k">\@</span>.  <span class="s">$</span><span class="nb">S_</span><span class="m">2</span><span class="s">$</span>, on the other hand, selects only
</div><div id="l95" class="code_block"><span class="k">\emph</span><span class="nb">{</span>relevant<span class="nb">}</span> answers of <span class="s">$</span><span class="nb">S</span><span class="s">$</span>, those where the returns satisfy
</div><div id="l96" class="code_block"><span class="k">\code</span><span class="nb">{</span><span class="k">\{</span>X=g(Z),Y=b<span class="k">\}</span><span class="nb">}</span>.<span class="k">\fillBox</span>
</div><div id="l97" class="code_block"><span class="k">\end</span><span class="nb">{</span>example<span class="nb">}</span>
</div><div id="l98" class="code_block">
</div><div id="l99" class="code_block"><span class="c">% - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
</div><div id="l100" class="code_block">
</div><div id="l101" class="code_block"><span class="k">\subsubsection*</span><span class="nb">{</span>Skeletons and Predicate Specifications<span class="nb">}</span>
</div><div id="l102" class="code_block">
</div><div id="l103" class="code_block"><span class="k">\index</span><span class="nb">{</span>skeleton<span class="nb">}</span>
</div><div id="l104" class="code_block">
</div><div id="l105" class="code_block">A <span class="k">\emph</span><span class="nb">{</span>skeleton<span class="nb">}</span> for a functor <span class="k">\code</span><span class="nb">{</span>f/n<span class="nb">}</span> is a structure of the form
</div><div id="l106" class="code_block"><span class="k">\code</span><span class="nb">{</span>f(<span class="s">$</span><span class="nb">Arg_</span><span class="m">1</span><span class="s">$</span>,<span class="k">\ldots</span>,<span class="s">$</span><span class="nb">Arg_n</span><span class="s">$</span>)<span class="nb">}</span> where each <span class="s">$</span><span class="nb">Arg_i</span><span class="s">$</span> is a distinct
</div><div id="l107" class="code_block">variable.  Similarly the skeleton of a term is the skeleton formed
</div><div id="l108" class="code_block">from the principal functor of the term, so that skeletons from the
</div><div id="l109" class="code_block">terms <span class="k">\code</span><span class="nb">{</span>f(1,2)<span class="nb">}</span> and <span class="k">\code</span><span class="nb">{</span>f(A,B)<span class="nb">}</span> are the same.  A <span class="k">\emph</span><span class="nb">{</span>return
</div><div id="l110" class="code_block">  skeleton<span class="nb">}</span> is a specific application of this notion to answer
</div><div id="l111" class="code_block">returns.  From it, one may discern the size of the template for a
</div><div id="l112" class="code_block">given subgoal.  Finally, we assume that a predicate specification for
</div><div id="l113" class="code_block">a predicate <span class="k">\code</span><span class="nb">{</span>p<span class="nb">}</span> and arity <span class="k">\code</span><span class="nb">{</span>n<span class="nb">}</span>, represented as
</div><div id="l114" class="code_block"><span class="k">\code</span><span class="nb">{</span>PredSpec<span class="nb">}</span> below, can be given either using the notation
</div><div id="l115" class="code_block"><span class="k">\code</span><span class="nb">{</span>p/n<span class="nb">}</span> or as a skeleton, <span class="k">\code</span><span class="nb">{</span>p(<span class="s">$</span><span class="nb">t_</span><span class="m">1</span><span class="s">$</span>,<span class="k">\ldots</span>,<span class="s">$</span><span class="nb">t_n</span><span class="s">$</span>)<span class="nb">}</span>.
</div><div id="l116" class="code_block">
</div><div id="l117" class="code_block"><span class="c">% - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
</div><div id="l118" class="code_block"><span class="k">\comment</span><span class="nb">{</span>
</div><div id="l119" class="code_block">| TLS: Unnecessary, as exceptions are described elsewhere
</div><div id="l120" class="code_block">| <span class="k">\subsubsection*</span><span class="nb">{</span>Exceptions<span class="nb">}</span>
</div><div id="l121" class="code_block">| 
</div><div id="l122" class="code_block">| Exceptions caught by the following predicates include:
</div><div id="l123" class="code_block">| <span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l124" class="code_block">| <span class="k">\item</span><span class="na">[Instantiation Error]</span> Argument is a variable.
</div><div id="l125" class="code_block">| <span class="k">\item</span><span class="na">[Type Error]</span> Argument is not a predicate specification or callable term.
</div><div id="l126" class="code_block">| <span class="k">\item</span><span class="na">[Table Error]</span> Argument does not contain a tabled predicate, or a valid
</div><div id="l127" class="code_block">|         reference to a table component.
</div><div id="l128" class="code_block">| <span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l129" class="code_block"><span class="nb">}</span>
</div><div id="l130" class="code_block">
</div><div id="l131" class="code_block"><span class="c">%--------------------------------------------------------------------------</span>
</div><div id="l132" class="code_block">
</div><div id="l133" class="code_block"><span class="k">\subsection</span><span class="nb">{</span>Declaring and Modifying Tabled Predicates<span class="nb">}</span>
</div><div id="l134" class="code_block"><span class="k">\label</span><span class="nb">{</span>sec:TablePred:Decl<span class="nb">&amp;</span>Mod<span class="nb">}</span>
</div><div id="l135" class="code_block"><span class="k">\index</span><span class="nb">{</span>tabling!directives<span class="nb">}</span><span class="k">\index</span><span class="nb">{</span>tabling!strategy selection<span class="nb">}</span>
</div><div id="l136" class="code_block">
</div><div id="l137" class="code_block"><span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l138" class="code_block"><span class="c">% - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
</div><div id="l139" class="code_block">
</div><div id="l140" class="code_block"><span class="k">\index</span><span class="nb">{</span>tabling!call subsumption<span class="nb">}</span>
</div><div id="l141" class="code_block"><span class="k">\index</span><span class="nb">{</span>tabling!call variance<span class="nb">}</span>
</div><div id="l142" class="code_block"><span class="k">\index</span><span class="nb">{</span>tabling!answer subsumption<span class="nb">}</span>
</div><div id="l143" class="code_block"><span class="k">\index</span><span class="nb">{</span>tabling!incremental<span class="nb">}</span>
</div><div id="l144" class="code_block"><span class="k">\index</span><span class="nb">{</span>tabling!dynamic predicates<span class="nb">}</span>
</div><div id="l145" class="code_block"><span class="k">\index</span><span class="nb">{</span>tabling!private<span class="nb">}</span>
</div><div id="l146" class="code_block"><span class="k">\index</span><span class="nb">{</span>tabling!shared<span class="nb">}</span>
</div><div id="l147" class="code_block"><span class="k">\index</span><span class="nb">{</span>tabling!opaque<span class="nb">}</span>
</div><div id="l148" class="code_block">
</div><div id="l149" class="code_block"><span class="k">\label</span><span class="nb">{</span>table-declaration<span class="nb">}</span>
</div><div id="l150" class="code_block"><span class="k">\ourstandarditem</span><span class="nb">{</span>table(+Operations)<span class="nb">}{</span>table/1<span class="nb">}{</span>Tabling<span class="nb">}</span>
</div><div id="l151" class="code_block"><span class="c">%</span>
</div><div id="l152" class="code_block"><span class="nb">{</span><span class="k">\tt</span> table/1<span class="nb">}</span> can be used either as a compiler declaration or as an
</div><div id="l153" class="code_block">executable directive.  Used as a compiler declaration, it indicates
</div><div id="l154" class="code_block">that each predicate denoted by the command is to be compiled using (a
</div><div id="l155" class="code_block">particular form of) tabling, and may indicate that a predicate is
</div><div id="l156" class="code_block">dynamic or thread-shared or thread-private.  Executed as a directive
</div><div id="l157" class="code_block">in a state of execution where no clauses exist for each denoted
</div><div id="l158" class="code_block">predicate <span class="nb">{</span><span class="k">\tt</span> table/1<span class="nb">}</span> ensures that any clauses asserted for each
</div><div id="l159" class="code_block">predicate use tabling and may indicate the mode of tabling to be used.
</div><div id="l160" class="code_block"><span class="nb">{</span><span class="k">\tt</span> Operations<span class="nb">}</span> can take one of three forms:
</div><div id="l161" class="code_block"><span class="c">%</span>
</div><div id="l162" class="code_block"><span class="k">\begin</span><span class="nb">{</span>enumerate<span class="nb">}</span>
</div><div id="l163" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> Operations<span class="nb">}</span> is a predicate indicator, a callable term, or
</div><div id="l164" class="code_block">  a comma-list or list of predicate indicators or callable terms.
</div><div id="l165" class="code_block"><span class="c">%</span>
</div><div id="l166" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> Operations<span class="nb">}</span> is a term indicating that a predicate is to be
</div><div id="l167" class="code_block">  tabled with a particular form of answer subsumption
</div><div id="l168" class="code_block">  (cf. Section~<span class="k">\ref</span><span class="nb">{</span>sec:table-aggregation<span class="nb">}</span>).
</div><div id="l169" class="code_block"><span class="c">%</span>
</div><div id="l170" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> Operations<span class="nb">}</span> has the form <span class="nb">{</span><span class="k">\tt</span> Predspec as Options<span class="nb">}</span> where
</div><div id="l171" class="code_block"><span class="k">\bi</span>
</div><div id="l172" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> PredSpec<span class="nb">}</span> is a predicate indicator, a callable term, or p
</div><div id="l173" class="code_block">  comma-list or list of predicate indicators or callable terms.
</div><div id="l174" class="code_block"><span class="c">%</span>
</div><div id="l175" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> Options<span class="nb">}</span> is either a table option or a list of table
</div><div id="l176" class="code_block">  options.  In <span class="k">\version</span>, the following table options are supported
</div><div id="l177" class="code_block"><span class="k">\bi</span>
</div><div id="l178" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> dynamic<span class="nb">}</span> or <span class="nb">{</span><span class="k">\tt</span> dyn<span class="nb">}</span> which causes the predicate(s) to be
</div><div id="l179" class="code_block">  treated as dynamic in addition to being tabled, and is equivalent to
</div><div id="l180" class="code_block">  <span class="nb">{</span><span class="k">\tt</span> ?- dynamic PredSpec<span class="nb">}</span>~<span class="k">\footnote</span><span class="nb">{</span>Because dynamic is an operator,
</div><div id="l181" class="code_block">    the declaration requires parentheses, e.g.: <span class="nb">{</span><span class="k">\tt</span> table p/n as
</div><div id="l182" class="code_block">      (dynamic).<span class="nb">}}</span>
</div><div id="l183" class="code_block"><span class="c">%</span>
</div><div id="l184" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> subsumptive<span class="nb">}</span> which causes the table evaluation method of
</div><div id="l185" class="code_block">  the predicate(s) to use call subsumption.
</div><div id="l186" class="code_block"><span class="c">%</span>
</div><div id="l187" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> variant<span class="nb">}</span> which causes the table evaluation method of the
</div><div id="l188" class="code_block">  predicate(s) to use call variance.
</div><div id="l189" class="code_block"><span class="c">%</span>
</div><div id="l190" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> incremental<span class="nb">}</span> which causes the table evaluation method of
</div><div id="l191" class="code_block">  the predicate(s) to be incremental.
</div><div id="l192" class="code_block"><span class="c">%</span>
</div><div id="l193" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> opaque<span class="nb">}</span> which indicates that the tables predicate is used
</div><div id="l194" class="code_block">  in the definition of an incremental table, but are not to be
</div><div id="l195" class="code_block">  incrementally maintained themselves.  
</div><div id="l196" class="code_block"><span class="c">%</span>
</div><div id="l197" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> private<span class="nb">}</span> which causes the predicate(s) to be treated as
</div><div id="l198" class="code_block">  thread private in addition to being tabled.
</div><div id="l199" class="code_block"><span class="c">%</span>
</div><div id="l200" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> shared<span class="nb">}</span> which causes the predicate(s) to be treated as
</div><div id="l201" class="code_block">  thread shared in addition to being tabled.
</div><div id="l202" class="code_block"><span class="k">\ei</span>
</div><div id="l203" class="code_block"><span class="k">\ei</span>
</div><div id="l204" class="code_block"><span class="k">\end</span><span class="nb">{</span>enumerate<span class="nb">}</span>
</div><div id="l205" class="code_block">
</div><div id="l206" class="code_block">If the directive 
</div><div id="l207" class="code_block">
</div><div id="l208" class="code_block"><span class="nb">{</span><span class="k">\tt</span>  table <span class="s">$</span><span class="nb">PredList</span><span class="s">$</span> as <span class="s">$</span><span class="nb">Options</span><span class="s">$</span>.<span class="nb">}</span>
</div><div id="l209" class="code_block">
</div><div id="l210" class="code_block">is executed, various checks are performed on <span class="s">$</span><span class="nb">Options</span><span class="s">$</span>.  These checks
</div><div id="l211" class="code_block">are (mostly) performed before any predicates are declared as dynamic
</div><div id="l212" class="code_block">or options changed, and reduce the possibility of leaving some <span class="s">$</span><span class="nb">p</span><span class="o">/</span><span class="nb">n</span><span class="s">$</span>
</div><div id="l213" class="code_block">in <span class="s">$</span><span class="nb">PredList</span><span class="s">$</span> with inconsistent attributes.
</div><div id="l214" class="code_block"><span class="c">%</span>
</div><div id="l215" class="code_block"><span class="k">\begin</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l216" class="code_block"><span class="k">\item</span> If a predicate in <span class="nb">{</span><span class="k">\tt</span> Predlist<span class="nb">}</span> has been declared as <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l217" class="code_block">  incremental<span class="nb">}</span> it may be changed to <span class="nb">{</span><span class="k">\tt</span> opaque<span class="nb">}</span> at any time;
</div><div id="l218" class="code_block">  similarly, a predicate that is <span class="nb">{</span><span class="k">\tt</span> opaque<span class="nb">}</span> may be changed to <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l219" class="code_block">    incremental<span class="nb">}</span>
</div><div id="l220" class="code_block"><span class="c">%</span>
</div><div id="l221" class="code_block"><span class="k">\item</span> If a predicate in <span class="nb">{</span><span class="k">\tt</span> Predlist<span class="nb">}</span> has been declared to use call
</div><div id="l222" class="code_block">  variance it may be changed to use call subsumption at any time;
</div><div id="l223" class="code_block">  similarly, a predicate that uses call subsumption may be changed to
</div><div id="l224" class="code_block">  use call variance.
</div><div id="l225" class="code_block"><span class="c">%</span>
</div><div id="l226" class="code_block"><span class="k">\item</span> Otherwise, an attempt to change an attribute of <span class="s">$</span><span class="nb">p</span><span class="o">/</span><span class="nb">n</span><span class="s">$</span> in
</div><div id="l227" class="code_block">  <span class="s">$</span><span class="nb">PredList</span><span class="s">$</span> -- i.e. whether <span class="s">$</span><span class="nb">p</span><span class="o">/</span><span class="nb">n</span><span class="s">$</span> is tabled or not, dynamic or not
</div><div id="l228" class="code_block">  and thread-private or thread-shared -- will throw a permission
</div><div id="l229" class="code_block">  error.  
</div><div id="l230" class="code_block"><span class="k">\end</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l231" class="code_block">
</div><div id="l232" class="code_block">In addition, regardless of the state of predicates in <span class="s">$</span><span class="nb">PredList</span><span class="s">$</span>, if
</div><div id="l233" class="code_block">options contains an unsupported set of declarations, a table error
</div><div id="l234" class="code_block">will be thrown (see Table~<span class="k">\ref</span><span class="nb">{</span>table:table<span class="nb">}</span> for a list of supported
</div><div id="l235" class="code_block">and non-supported combinations of tabling modes and predicate
</div><div id="l236" class="code_block">properties).  <span class="nb">{</span><span class="k">\tt</span> Options<span class="nb">}</span> is throws a table error in the following
</div><div id="l237" class="code_block">cases:
</div><div id="l238" class="code_block"><span class="c">%</span>
</div><div id="l239" class="code_block"><span class="k">\bi</span>
</div><div id="l240" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> Options<span class="nb">}</span> contains <span class="nb">{</span><span class="k">\tt</span> dynamic<span class="nb">}</span> and <span class="nb">{</span><span class="k">\tt</span> tabled<span class="nb">}</span> or <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l241" class="code_block">  variant<span class="nb">}</span> and <span class="nb">{</span><span class="k">\tt</span> opaque<span class="nb">}</span> or <span class="nb">{</span><span class="k">\tt</span> incremental<span class="nb">}</span>.  Tabled dynamic
</div><div id="l242" class="code_block">  incremental code is not yet supported in XSB.
</div><div id="l243" class="code_block">
</div><div id="l244" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> Options<span class="nb">}</span> contains <span class="nb">{</span><span class="k">\tt</span> incremental<span class="nb">}</span> or <span class="nb">{</span><span class="k">\tt</span> opaque<span class="nb">}</span> and <span class="nb">{</span><span class="k">\tt</span> subsumptive<span class="nb">}</span> or <span class="nb">{</span><span class="k">\tt</span> shared<span class="nb">}</span> 
</div><div id="l245" class="code_block">
</div><div id="l246" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> Options<span class="nb">}</span> contains both <span class="nb">{</span><span class="k">\tt</span> subsumptive<span class="nb">}</span> and <span class="nb">{</span><span class="k">\tt</span> shared<span class="nb">}</span>
</div><div id="l247" class="code_block"><span class="c">%</span>
</div><div id="l248" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> Options<span class="nb">}</span> contains both <span class="nb">{</span><span class="k">\tt</span> variant<span class="nb">}</span> and <span class="nb">{</span><span class="k">\tt</span> subsumptive<span class="nb">}</span>
</div><div id="l249" class="code_block"><span class="c">%</span>
</div><div id="l250" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> Options<span class="nb">}</span> contains both <span class="nb">{</span><span class="k">\tt</span> private<span class="nb">}</span> and <span class="nb">{</span><span class="k">\tt</span> shared<span class="nb">}</span>
</div><div id="l251" class="code_block"><span class="c">%</span>
</div><div id="l252" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> Options<span class="nb">}</span> contains both <span class="nb">{</span><span class="k">\tt</span> incremental<span class="nb">}</span> and <span class="nb">{</span><span class="k">\tt</span> opaque<span class="nb">}</span>
</div><div id="l253" class="code_block"><span class="k">\ei</span>
</div><div id="l254" class="code_block">
</div><div id="l255" class="code_block"><span class="nb">{</span><span class="k">\bf</span> Error Cases<span class="nb">}</span>
</div><div id="l256" class="code_block">
</div><div id="l257" class="code_block">Error cases are summarized as follows.  Let <span class="nb">{</span><span class="k">\tt</span> Operations<span class="nb">}</span> be of the
</div><div id="l258" class="code_block">form <span class="nb">{</span><span class="k">\tt</span> PredSpec<span class="nb">}</span> or <span class="nb">{</span><span class="k">\tt</span> PredSpec<span class="nb">}</span> as <span class="nb">{</span><span class="k">\tt</span> Options<span class="nb">}</span>.  Then if 
</div><div id="l259" class="code_block"><span class="c">%</span>
</div><div id="l260" class="code_block"><span class="k">\bi</span>
</div><div id="l261" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> PredSpec<span class="nb">}</span> or is a variable or a comma list containing a variable
</div><div id="l262" class="code_block"><span class="k">\bi</span>
</div><div id="l263" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> instantiation<span class="k">\_error</span><span class="nb">}</span>
</div><div id="l264" class="code_block"><span class="k">\ei</span>
</div><div id="l265" class="code_block"><span class="k">\item</span> An element of <span class="nb">{</span><span class="k">\tt</span> PredSpec<span class="nb">}</span> is neither a variable nor a comma
</div><div id="l266" class="code_block">  list
</div><div id="l267" class="code_block"><span class="k">\bi</span>
</div><div id="l268" class="code_block"><span class="k">\item</span> 	<span class="nb">{</span><span class="k">\tt</span> type<span class="k">\_error</span>(callable,PredSpec)<span class="nb">}</span>
</div><div id="l269" class="code_block"><span class="k">\ei</span>
</div><div id="l270" class="code_block"><span class="k">\item</span> A predicate in <span class="nb">{</span><span class="k">\tt</span> PredSpec<span class="nb">}</span> has been previously defined to be
</div><div id="l271" class="code_block">  static or foreign and <span class="nb">{</span><span class="k">\tt</span> Options<span class="nb">}</span> contains <span class="nb">{</span><span class="k">\tt</span> dynamic<span class="nb">}</span> or <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l272" class="code_block">    dyn<span class="nb">}</span>
</div><div id="l273" class="code_block"><span class="k">\bi</span>
</div><div id="l274" class="code_block"><span class="k">\item</span> 	<span class="nb">{</span><span class="k">\tt</span> permission<span class="k">\_error</span>(modify,static<span class="k">\_predicate</span>)<span class="nb">}</span>
</div><div id="l275" class="code_block"><span class="k">\ei</span>
</div><div id="l276" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> Options<span class="nb">}</span> is a variable or a list containing a variable
</div><div id="l277" class="code_block"><span class="k">\bi</span>
</div><div id="l278" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> instantiation<span class="k">\_error</span><span class="nb">}</span>
</div><div id="l279" class="code_block"><span class="k">\ei</span>
</div><div id="l280" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> Options<span class="nb">}</span> contains an element <span class="nb">{</span><span class="k">\tt</span> Option<span class="nb">}</span> that isn&#39;t a table option (as described above)
</div><div id="l281" class="code_block"><span class="k">\bi</span>
</div><div id="l282" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> domain<span class="k">\_error</span>(table<span class="k">\_option</span>,Option)<span class="nb">}</span>
</div><div id="l283" class="code_block"><span class="k">\ei</span>
</div><div id="l284" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> Options<span class="nb">}</span> contains a non-supported combination of  elements (as described above)
</div><div id="l285" class="code_block"><span class="k">\bi</span>
</div><div id="l286" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> table<span class="k">\_error</span><span class="nb">}</span>
</div><div id="l287" class="code_block"><span class="k">\ei</span>
</div><div id="l288" class="code_block"><span class="k">\item</span> An option in <span class="nb">{</span><span class="k">\tt</span> Options<span class="nb">}</span> would modify a predicate in predspec
</div><div id="l289" class="code_block">  in a manner that is not allowed (as described above)
</div><div id="l290" class="code_block"><span class="k">\bi</span>
</div><div id="l291" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> permission<span class="k">\_error</span><span class="nb">}</span>
</div><div id="l292" class="code_block"><span class="k">\ei</span>
</div><div id="l293" class="code_block"><span class="k">\ei</span>
</div><div id="l294" class="code_block">
</div><div id="l295" class="code_block"><span class="c">% - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
</div><div id="l296" class="code_block">
</div><div id="l297" class="code_block"><span class="c">% \ourstandarditem{use\_subsumptive\_tabling\ \ +PredSpec$_1$, \ldots, +PredSpec$_k$.}{use\_subsumptive\_tabling/1}{Tabling}</span>
</div><div id="l298" class="code_block"><span class="c">%</span>
</div><div id="l299" class="code_block"><span class="c">%</span>
</div><div id="l300" class="code_block"><span class="c">% Declares each \emph{tabled predicate} denoted by \code{PredSpec$_i$}</span>
</div><div id="l301" class="code_block"><span class="c">% to use call-subsumption, thus overriding the system default of call</span>
</div><div id="l302" class="code_block"><span class="c">% variance~\footnote{If XSB is called with the {\tt -S} option the</span>
</div><div id="l303" class="code_block"><span class="c">%   default will be to use call subsumption}.  The tabling strategy can</span>
</div><div id="l304" class="code_block"><span class="c">% be changed at will through the invocation of this and the following</span>
</div><div id="l305" class="code_block"><span class="c">% predicate.  Note, however, that the table for the predicate must be</span>
</div><div id="l306" class="code_block"><span class="c">% empty at the time of the change.</span>
</div><div id="l307" class="code_block">
</div><div id="l308" class="code_block"><span class="c">% - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
</div><div id="l309" class="code_block">
</div><div id="l310" class="code_block"><span class="c">% \ourstandarditem{use\_variant\_tabling\ \ +PredSpec$_1$, \ldots, +PredSpec$_k$.}{use\_variant\_tabling/1}{Tabling}</span>
</div><div id="l311" class="code_block"><span class="c">%</span>
</div><div id="l312" class="code_block"><span class="c">% Declares each \emph{tabled predicate} denoted by \code{PredSpec$_i$}</span>
</div><div id="l313" class="code_block"><span class="c">% to use call-variance, thus overriding the system default if XSB is</span>
</div><div id="l314" class="code_block"><span class="c">% called with the {\tt -S} option.  The same comments apply as for {\tt</span>
</div><div id="l315" class="code_block"><span class="c">%   use\_subsumptive\_tabling/1}.</span>
</div><div id="l316" class="code_block">
</div><div id="l317" class="code_block"><span class="c">% - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
</div><div id="l318" class="code_block"><span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l319" class="code_block">
</div><div id="l320" class="code_block"><span class="c">%--------------------------------------------------------------------------</span>
</div><div id="l321" class="code_block">
</div><div id="l322" class="code_block"><span class="k">\subsection</span><span class="nb">{</span>Predicates for Table Inspection<span class="nb">}</span>
</div><div id="l323" class="code_block"><span class="k">\label</span><span class="nb">{</span>sec:TablePred:Inspection<span class="nb">}</span>
</div><div id="l324" class="code_block"><span class="k">\index</span><span class="nb">{</span>tabling!table inspection<span class="nb">}</span>
</div><div id="l325" class="code_block"><span class="k">\index</span><span class="nb">{</span>tabling!call subsumption<span class="nb">}</span>
</div><div id="l326" class="code_block"><span class="k">\index</span><span class="nb">{</span>tabling!call variance<span class="nb">}</span>
</div><div id="l327" class="code_block">
</div><div id="l328" class="code_block">The user should be aware that skeletons that are dynamically created
</div><div id="l329" class="code_block">(e.g., by <span class="k">\code</span><span class="nb">{</span>functor/3<span class="nb">}</span>) are located in <span class="nb">{</span><span class="k">\tt</span> usermod<span class="nb">}</span> (refer to
</div><div id="l330" class="code_block"><span class="k">\refsec</span><span class="nb">{</span>Modules<span class="nb">}</span>).  In such a case, the tabling predicates below may
</div><div id="l331" class="code_block">not behave in the desired manner if the tabled predicates themselves
</div><div id="l332" class="code_block">have not been imported into <span class="nb">{</span><span class="k">\tt</span> usermod<span class="nb">}</span>.
</div><div id="l333" class="code_block">
</div><div id="l334" class="code_block">We maintain two running examples in this section for explanatory
</div><div id="l335" class="code_block">purposes.  One uses variant-based tabling:
</div><div id="l336" class="code_block"><span class="c">%</span>
</div><div id="l337" class="code_block"><span class="k">\begin</span><span class="nb">{</span>center<span class="nb">}</span>
</div><div id="l338" class="code_block"><span class="k">\begin</span><span class="nb">{</span>tabular<span class="nb">}{</span>cc<span class="nb">}</span><span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l339" class="code_block"><span class="k">\multicolumn</span><span class="nb">{</span>2<span class="nb">}{</span>c<span class="nb">}{</span><span class="k">\rule</span><span class="nb">{</span>0ex<span class="nb">}{</span>2.5ex<span class="nb">}</span><span class="k">\textbf</span><span class="nb">{</span>Variant Example<span class="nb">}}</span> <span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l340" class="code_block"><span class="k">\rule</span><span class="na">[-2ex]</span><span class="nb">{</span>0ex<span class="nb">}{</span>5ex<span class="nb">}</span> <span class="k">\textbf</span><span class="nb">{</span>Program<span class="nb">}</span> <span class="nb">&amp;</span> <span class="k">\textbf</span><span class="nb">{</span>Table<span class="nb">}</span> <span class="k">\\</span>
</div><div id="l341" class="code_block"><span class="k">\begin</span><span class="nb">{</span>minipage<span class="nb">}{</span>14.5em<span class="nb">}</span>
</div><div id="l342" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l343" class="code_block">:- table p/2 as variant.
</div><div id="l344" class="code_block">
</div><div id="l345" class="code_block">p(1,2).
</div><div id="l346" class="code_block">p(1,3).
</div><div id="l347" class="code_block">p(1,<span class="nb">_</span>).
</div><div id="l348" class="code_block">p(2,3).
</div><div id="l349" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l350" class="code_block"><span class="k">\end</span><span class="nb">{</span>minipage<span class="nb">}</span>
</div><div id="l351" class="code_block"><span class="nb">&amp;</span>
</div><div id="l352" class="code_block"><span class="k">\begin</span><span class="nb">{</span>tabular<span class="nb">}{</span>|c|c|c|<span class="nb">}</span> <span class="k">\hline</span>
</div><div id="l353" class="code_block">  Subgoal <span class="nb">&amp;</span> Answer Set <span class="nb">&amp;</span> Status<span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l354" class="code_block">  p(1,Y) <span class="nb">&amp;</span> p(1,2) <span class="nb">&amp;</span> complete <span class="k">\\</span> 
</div><div id="l355" class="code_block">         <span class="nb">&amp;</span> p(1,3) <span class="nb">&amp;</span> <span class="k">\\</span>
</div><div id="l356" class="code_block">         <span class="nb">&amp;</span> p(1,Y) <span class="nb">&amp;</span> <span class="k">\\</span> <span class="k">\hline</span>
</div><div id="l357" class="code_block">  p(X,3) <span class="nb">&amp;</span> p(1,3) <span class="nb">&amp;</span> complete <span class="k">\\</span> 
</div><div id="l358" class="code_block">         <span class="nb">&amp;</span> p(2,3) <span class="nb">&amp;</span> <span class="k">\\</span> <span class="k">\hline</span>
</div><div id="l359" class="code_block"><span class="k">\end</span><span class="nb">{</span>tabular<span class="nb">}</span> <span class="k">\\</span>
</div><div id="l360" class="code_block"><span class="k">\vspace*</span><span class="nb">{</span>-2ex<span class="nb">}</span> <span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l361" class="code_block"><span class="k">\end</span><span class="nb">{</span>tabular<span class="nb">}</span>
</div><div id="l362" class="code_block"><span class="k">\end</span><span class="nb">{</span>center<span class="nb">}</span>
</div><div id="l363" class="code_block">
</div><div id="l364" class="code_block"><span class="k">\noindent</span>
</div><div id="l365" class="code_block">and the other uses subsumption-based tabling:
</div><div id="l366" class="code_block">
</div><div id="l367" class="code_block"><span class="k">\begin</span><span class="nb">{</span>center<span class="nb">}</span>
</div><div id="l368" class="code_block"><span class="k">\begin</span><span class="nb">{</span>tabular<span class="nb">}{</span>cc<span class="nb">}</span><span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l369" class="code_block"><span class="k">\multicolumn</span><span class="nb">{</span>2<span class="nb">}{</span>c<span class="nb">}{</span><span class="k">\rule</span><span class="nb">{</span>0ex<span class="nb">}{</span>2.5ex<span class="nb">}</span><span class="k">\textbf</span><span class="nb">{</span>Subsumptive Example<span class="nb">}}</span> <span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l370" class="code_block"><span class="k">\rule</span><span class="na">[-2ex]</span><span class="nb">{</span>0ex<span class="nb">}{</span>5ex<span class="nb">}</span> <span class="k">\textbf</span><span class="nb">{</span>Program<span class="nb">}</span> <span class="nb">&amp;</span> <span class="k">\textbf</span><span class="nb">{</span>Table<span class="nb">}</span> <span class="k">\\</span>
</div><div id="l371" class="code_block"><span class="k">\begin</span><span class="nb">{</span>minipage<span class="nb">}{</span>17em<span class="nb">}</span>
</div><div id="l372" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l373" class="code_block">:- table q/2 as subsumptive.
</div><div id="l374" class="code_block">q(a,b).
</div><div id="l375" class="code_block">q(b,c).
</div><div id="l376" class="code_block">q(a,c).
</div><div id="l377" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l378" class="code_block"><span class="k">\end</span><span class="nb">{</span>minipage<span class="nb">}</span>
</div><div id="l379" class="code_block"><span class="nb">&amp;</span>
</div><div id="l380" class="code_block"><span class="k">\begin</span><span class="nb">{</span>tabular<span class="nb">}{</span>|c|c|c|<span class="nb">}</span> <span class="k">\hline</span>
</div><div id="l381" class="code_block">  Subgoal <span class="nb">&amp;</span> Answer Set <span class="nb">&amp;</span> Status <span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l382" class="code_block">  q(X,Y) <span class="nb">&amp;</span> q(a,b) <span class="nb">&amp;</span> complete <span class="k">\\</span>
</div><div id="l383" class="code_block">         <span class="nb">&amp;</span> q(b,c) <span class="nb">&amp;</span> <span class="k">\\</span>
</div><div id="l384" class="code_block">         <span class="nb">&amp;</span> q(a,c) <span class="nb">&amp;</span> <span class="k">\\</span> <span class="k">\hline</span>
</div><div id="l385" class="code_block">  q(a,Y) <span class="nb">&amp;</span> <span class="k">\textit</span><span class="nb">{</span>q(a,b)<span class="nb">}</span> <span class="nb">&amp;</span> complete <span class="k">\\</span>
</div><div id="l386" class="code_block">         <span class="nb">&amp;</span> <span class="k">\textit</span><span class="nb">{</span>q(a,c)<span class="nb">}</span> <span class="nb">&amp;</span> <span class="k">\\</span> <span class="k">\hline</span>
</div><div id="l387" class="code_block">  q(X,c) <span class="nb">&amp;</span> <span class="k">\textit</span><span class="nb">{</span>q(b,c)<span class="nb">}</span> <span class="nb">&amp;</span> complete <span class="k">\\</span>
</div><div id="l388" class="code_block">         <span class="nb">&amp;</span> <span class="k">\textit</span><span class="nb">{</span>q(a,c)<span class="nb">}</span> <span class="nb">&amp;</span> <span class="k">\\</span> <span class="k">\hline</span>
</div><div id="l389" class="code_block"><span class="k">\end</span><span class="nb">{</span>tabular<span class="nb">}</span> <span class="k">\\</span>
</div><div id="l390" class="code_block"><span class="k">\vspace*</span><span class="nb">{</span>-2ex<span class="nb">}</span> <span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l391" class="code_block"><span class="k">\end</span><span class="nb">{</span>tabular<span class="nb">}</span>
</div><div id="l392" class="code_block"><span class="k">\end</span><span class="nb">{</span>center<span class="nb">}</span>
</div><div id="l393" class="code_block">
</div><div id="l394" class="code_block"><span class="k">\noindent</span>
</div><div id="l395" class="code_block">Note that in the subsumptive example, the subgoals <span class="k">\code</span><span class="nb">{</span>q(a,Y)<span class="nb">}</span> and
</div><div id="l396" class="code_block"><span class="k">\code</span><span class="nb">{</span>q(X,c)<span class="nb">}</span> are subsumed by, and hence obtain their answers from,
</div><div id="l397" class="code_block">the subgoal <span class="k">\code</span><span class="nb">{</span>q(X,Y)<span class="nb">}</span><span class="k">\@</span>.
</div><div id="l398" class="code_block">
</div><div id="l399" class="code_block"><span class="k">\vspace</span><span class="nb">{</span>2ex<span class="nb">}</span>
</div><div id="l400" class="code_block">
</div><div id="l401" class="code_block"><span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l402" class="code_block">
</div><div id="l403" class="code_block"><span class="c">% - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
</div><div id="l404" class="code_block">
</div><div id="l405" class="code_block"><span class="k">\ourstandarditem</span><span class="nb">{</span>get<span class="k">\_call</span>(+CallTerm,-TableEntryHandle,-ReturnTemplate)<span class="nb">}{</span>get<span class="k">\_call</span>/3<span class="nb">}{</span>Tabling<span class="nb">}</span>
</div><div id="l406" class="code_block">
</div><div id="l407" class="code_block"><span class="c">%</span>
</div><div id="l408" class="code_block"><span class="k">\index</span><span class="nb">{</span>tabling!call subsumption<span class="nb">}</span>
</div><div id="l409" class="code_block"><span class="k">\index</span><span class="nb">{</span>tabling!call variance<span class="nb">}</span>
</div><div id="l410" class="code_block">If call variance is used for the predicate corresponding to <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l411" class="code_block">  CallTerm<span class="nb">}</span>, then this predicate searches the table for an entry whose
</div><div id="l412" class="code_block">subgoal is a <span class="k">\emph</span><span class="nb">{</span>variant<span class="nb">}</span> of <span class="k">\code</span><span class="nb">{</span>CallTerm<span class="nb">}</span>.  If subsumption is
</div><div id="l413" class="code_block">used, then this predicate searches for some entry that subsumes
</div><div id="l414" class="code_block">(properly or not) <span class="nb">{</span><span class="k">\tt</span> CallTerm<span class="nb">}</span>.  In either case, should the entry
</div><div id="l415" class="code_block">exist, then the handle to this entry is assigned to the second
</div><div id="l416" class="code_block">argument, while in the third, its return template is constructed.
</div><div id="l417" class="code_block">These latter two arguments should be given as variables.
</div><div id="l418" class="code_block">
</div><div id="l419" class="code_block"><span class="nb">{</span><span class="k">\bf</span> Error Cases<span class="nb">}</span>
</div><div id="l420" class="code_block"><span class="k">\bi</span>
</div><div id="l421" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> CallTerm<span class="nb">}</span> is not a callable term
</div><div id="l422" class="code_block"><span class="k">\bi</span>
</div><div id="l423" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> type<span class="k">\_error</span>(callable<span class="k">\_term</span>,CallTerm)<span class="nb">}</span>
</div><div id="l424" class="code_block"><span class="k">\ei</span>
</div><div id="l425" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> CallTerm<span class="nb">}</span> does not correspond to a tabled predicate
</div><div id="l426" class="code_block"><span class="k">\bi</span>
</div><div id="l427" class="code_block"><span class="k">\item</span> 	<span class="nb">{</span><span class="k">\tt</span> permission<span class="k">\_error</span>(table access,non-tabled predicate,<span class="nb">{</span><span class="k">\tt</span> CallTerm<span class="nb">}</span>)<span class="nb">}</span>
</div><div id="l428" class="code_block">
</div><div id="l429" class="code_block"><span class="k">\ei</span>
</div><div id="l430" class="code_block"><span class="k">\ei</span>
</div><div id="l431" class="code_block"><span class="k">\</span> <span class="k">\\</span>
</div><div id="l432" class="code_block"><span class="k">\begin</span><span class="nb">{</span>minipage<span class="nb">}{</span>6in<span class="nb">}</span>
</div><div id="l433" class="code_block"><span class="k">\begin</span><span class="nb">{</span>example<span class="nb">}</span><span class="k">\</span> <span class="k">\\</span>
</div><div id="l434" class="code_block"> <span class="k">\\</span>
</div><div id="l435" class="code_block"><span class="k">\begin</span><span class="nb">{</span>tabular<span class="nb">}{</span>l@<span class="nb">{</span><span class="k">\hspace</span><span class="nb">{</span>4em<span class="nb">}}</span>r<span class="nb">}</span>
</div><div id="l436" class="code_block"><span class="k">\begin</span><span class="nb">{</span>tabular<span class="nb">}{</span>c<span class="nb">}</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l437" class="code_block"><span class="k">\rule</span><span class="nb">{</span>0ex<span class="nb">}{</span>2.5ex<span class="nb">}</span><span class="k">\textbf</span><span class="nb">{</span>Variant Predicate<span class="nb">}</span> <span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l438" class="code_block"><span class="k">\vspace*</span><span class="nb">{</span>-1ex<span class="nb">}</span> <span class="k">\\</span>
</div><div id="l439" class="code_block"><span class="k">\begin</span><span class="nb">{</span>minipage<span class="nb">}{</span>14.5em<span class="nb">}</span>
</div><div id="l440" class="code_block"><span class="k">\begin</span><span class="nb">{</span>small<span class="nb">}</span>
</div><div id="l441" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l442" class="code_block">| ?- get<span class="nb">_</span>call(p(X,Y),Ent,Ret).
</div><div id="l443" class="code_block">
</div><div id="l444" class="code_block">no
</div><div id="l445" class="code_block">| ?- get<span class="nb">_</span>call(p(1,Y),Ent,Ret).
</div><div id="l446" class="code_block">
</div><div id="l447" class="code_block">Y = <span class="nb">_</span>h92
</div><div id="l448" class="code_block">Ent = 136039108
</div><div id="l449" class="code_block">Ret = ret(<span class="nb">_</span>h92);
</div><div id="l450" class="code_block">
</div><div id="l451" class="code_block">no
</div><div id="l452" class="code_block">| ?- get<span class="nb">_</span>call(p(X,3),Ent,Ret).
</div><div id="l453" class="code_block">
</div><div id="l454" class="code_block">X = <span class="nb">_</span>h84
</div><div id="l455" class="code_block">Ent = 136039156
</div><div id="l456" class="code_block">Ret = ret(<span class="nb">_</span>h84);
</div><div id="l457" class="code_block">
</div><div id="l458" class="code_block">no
</div><div id="l459" class="code_block">| ?- get<span class="nb">_</span>call(p(1,3),Ent,Ret).
</div><div id="l460" class="code_block">
</div><div id="l461" class="code_block">no
</div><div id="l462" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l463" class="code_block"><span class="k">\end</span><span class="nb">{</span>small<span class="nb">}</span>
</div><div id="l464" class="code_block"><span class="k">\end</span><span class="nb">{</span>minipage<span class="nb">}</span> <span class="k">\\</span>
</div><div id="l465" class="code_block"><span class="k">\vspace*</span><span class="nb">{</span>-1ex<span class="nb">}</span> <span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l466" class="code_block"><span class="k">\end</span><span class="nb">{</span>tabular<span class="nb">}</span>
</div><div id="l467" class="code_block"> <span class="nb">&amp;</span>
</div><div id="l468" class="code_block"><span class="k">\begin</span><span class="nb">{</span>tabular<span class="nb">}{</span>c<span class="nb">}</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l469" class="code_block"><span class="k">\rule</span><span class="nb">{</span>0ex<span class="nb">}{</span>2.5ex<span class="nb">}</span><span class="k">\textbf</span><span class="nb">{</span>Subsumptive Predicate<span class="nb">}</span> <span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l470" class="code_block"><span class="k">\vspace*</span><span class="nb">{</span>-1ex<span class="nb">}</span> <span class="k">\\</span>
</div><div id="l471" class="code_block"><span class="k">\begin</span><span class="nb">{</span>minipage<span class="nb">}{</span>14.5em<span class="nb">}</span>
</div><div id="l472" class="code_block"><span class="k">\begin</span><span class="nb">{</span>small<span class="nb">}</span>
</div><div id="l473" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l474" class="code_block">| ?- get<span class="nb">_</span>call(q(X,Y),Ent,Ret).
</div><div id="l475" class="code_block">
</div><div id="l476" class="code_block">X = <span class="nb">_</span>h80
</div><div id="l477" class="code_block">Y = <span class="nb">_</span>h94
</div><div id="l478" class="code_block">Ent = 136043988
</div><div id="l479" class="code_block">Ret = ret(<span class="nb">_</span>h80,<span class="nb">_</span>h94);
</div><div id="l480" class="code_block">
</div><div id="l481" class="code_block">no
</div><div id="l482" class="code_block">| ?- get<span class="nb">_</span>call(q(a,Y),Ent,Ret).
</div><div id="l483" class="code_block">
</div><div id="l484" class="code_block">Y = <span class="nb">_</span>h88
</div><div id="l485" class="code_block">Ent = 136069412
</div><div id="l486" class="code_block">Ret = ret(a,<span class="nb">_</span>h88);
</div><div id="l487" class="code_block">
</div><div id="l488" class="code_block">no
</div><div id="l489" class="code_block">| ?- get<span class="nb">_</span>call(q(X,c),Ent,Ret).
</div><div id="l490" class="code_block">
</div><div id="l491" class="code_block">X = <span class="nb">_</span>h80
</div><div id="l492" class="code_block">Ent = 136069444
</div><div id="l493" class="code_block">Ret = ret(<span class="nb">_</span>h80,c);
</div><div id="l494" class="code_block">
</div><div id="l495" class="code_block">no
</div><div id="l496" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l497" class="code_block"><span class="k">\end</span><span class="nb">{</span>small<span class="nb">}</span>
</div><div id="l498" class="code_block"><span class="k">\end</span><span class="nb">{</span>minipage<span class="nb">}</span> <span class="k">\\</span>
</div><div id="l499" class="code_block"><span class="k">\vspace*</span><span class="nb">{</span>-1ex<span class="nb">}</span> <span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l500" class="code_block"><span class="k">\end</span><span class="nb">{</span>tabular<span class="nb">}</span>
</div><div id="l501" class="code_block"><span class="k">\end</span><span class="nb">{</span>tabular<span class="nb">}</span>
</div><div id="l502" class="code_block"><span class="k">\end</span><span class="nb">{</span>example<span class="nb">}</span>
</div><div id="l503" class="code_block"><span class="k">\end</span><span class="nb">{</span>minipage<span class="nb">}</span> <span class="k">\\</span>
</div><div id="l504" class="code_block">
</div><div id="l505" class="code_block"><span class="c">% - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
</div><div id="l506" class="code_block">
</div><div id="l507" class="code_block"><span class="k">\ourstandarditem</span><span class="nb">{</span>get<span class="k">\_calls</span>(<span class="k">\#</span>CallTerm,-TableEntryHandle,-ReturnSkeleton)<span class="nb">}{</span>get<span class="k">\_calls</span>/3<span class="nb">}{</span>Tabling<span class="nb">}</span>
</div><div id="l508" class="code_block"><span class="c">%</span>
</div><div id="l509" class="code_block">Identifies through backtracking each subgoal in the table which
</div><div id="l510" class="code_block">unifies with <span class="k">\code</span><span class="nb">{</span>CallTerm<span class="nb">}</span>.  For those that do, the handle to the
</div><div id="l511" class="code_block">table entry is assigned to the second argument, and its return
</div><div id="l512" class="code_block">skeleton is constructed in the third.  These latter two arguments
</div><div id="l513" class="code_block">should be given as variables.  The error terms are the same as for
</div><div id="l514" class="code_block"><span class="nb">{</span><span class="k">\tt</span> get<span class="k">\_calls</span>/1<span class="nb">}</span>.
</div><div id="l515" class="code_block">
</div><div id="l516" class="code_block"><span class="k">\begin</span><span class="nb">{</span>minipage<span class="nb">}{</span>6in<span class="nb">}</span>
</div><div id="l517" class="code_block"><span class="k">\begin</span><span class="nb">{</span>example<span class="nb">}</span><span class="k">\</span> <span class="k">\\</span>
</div><div id="l518" class="code_block"><span class="k">\\</span>
</div><div id="l519" class="code_block"><span class="k">\begin</span><span class="nb">{</span>tabular<span class="nb">}{</span>l@<span class="nb">{</span><span class="k">\hspace</span><span class="nb">{</span>4em<span class="nb">}}</span>r<span class="nb">}</span>
</div><div id="l520" class="code_block"><span class="k">\begin</span><span class="nb">{</span>tabular<span class="nb">}{</span>c<span class="nb">}</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l521" class="code_block"><span class="k">\rule</span><span class="nb">{</span>0ex<span class="nb">}{</span>2.5ex<span class="nb">}</span><span class="k">\textbf</span><span class="nb">{</span>Variant Predicate<span class="nb">}</span> <span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l522" class="code_block"><span class="k">\vspace*</span><span class="nb">{</span>-1ex<span class="nb">}</span> <span class="k">\\</span>
</div><div id="l523" class="code_block"><span class="k">\begin</span><span class="nb">{</span>minipage<span class="nb">}{</span>15em<span class="nb">}</span>
</div><div id="l524" class="code_block"><span class="k">\begin</span><span class="nb">{</span>small<span class="nb">}</span>
</div><div id="l525" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l526" class="code_block">| ?- get<span class="nb">_</span>calls(p(X,Y),Ent,Ret).
</div><div id="l527" class="code_block">
</div><div id="l528" class="code_block">X = <span class="nb">_</span>h80
</div><div id="l529" class="code_block">Y = 3
</div><div id="l530" class="code_block">Ent = 136039156
</div><div id="l531" class="code_block">Ret = ret(<span class="nb">_</span>h80);
</div><div id="l532" class="code_block">
</div><div id="l533" class="code_block">X = 1
</div><div id="l534" class="code_block">Y = <span class="nb">_</span>h94
</div><div id="l535" class="code_block">Ent = 136039108
</div><div id="l536" class="code_block">Ret = ret(<span class="nb">_</span>h94);
</div><div id="l537" class="code_block">
</div><div id="l538" class="code_block">no
</div><div id="l539" class="code_block">| ?- get<span class="nb">_</span>calls(p(X,3),Ent,Ret).
</div><div id="l540" class="code_block">
</div><div id="l541" class="code_block">X = <span class="nb">_</span>h80
</div><div id="l542" class="code_block">Ent = 136039156
</div><div id="l543" class="code_block">Ret = ret(<span class="nb">_</span>h80);
</div><div id="l544" class="code_block">
</div><div id="l545" class="code_block">X = 1
</div><div id="l546" class="code_block">Ent = 136039108
</div><div id="l547" class="code_block">Ret = ret(3);
</div><div id="l548" class="code_block">
</div><div id="l549" class="code_block">no
</div><div id="l550" class="code_block">| ?- get<span class="nb">_</span>calls(p(1,3),Ent,Ret).
</div><div id="l551" class="code_block">
</div><div id="l552" class="code_block">Ent = 136039156
</div><div id="l553" class="code_block">Ret = ret(1);
</div><div id="l554" class="code_block">
</div><div id="l555" class="code_block">Ent = 136039108
</div><div id="l556" class="code_block">Ret = ret(3);
</div><div id="l557" class="code_block">
</div><div id="l558" class="code_block">no
</div><div id="l559" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l560" class="code_block"><span class="k">\end</span><span class="nb">{</span>small<span class="nb">}</span>
</div><div id="l561" class="code_block"><span class="k">\end</span><span class="nb">{</span>minipage<span class="nb">}</span> <span class="k">\\</span>
</div><div id="l562" class="code_block"><span class="k">\vspace*</span><span class="nb">{</span>-1ex<span class="nb">}</span> <span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l563" class="code_block"><span class="k">\end</span><span class="nb">{</span>tabular<span class="nb">}</span>
</div><div id="l564" class="code_block"> <span class="nb">&amp;</span>
</div><div id="l565" class="code_block"><span class="k">\begin</span><span class="nb">{</span>tabular<span class="nb">}{</span>c<span class="nb">}</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l566" class="code_block"><span class="k">\rule</span><span class="nb">{</span>0ex<span class="nb">}{</span>2.5ex<span class="nb">}</span><span class="k">\textbf</span><span class="nb">{</span>Subsumptive Predicate<span class="nb">}</span> <span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l567" class="code_block"><span class="k">\vspace*</span><span class="nb">{</span>-1ex<span class="nb">}</span> <span class="k">\\</span>
</div><div id="l568" class="code_block"><span class="k">\begin</span><span class="nb">{</span>minipage<span class="nb">}{</span>15em<span class="nb">}</span>
</div><div id="l569" class="code_block"><span class="k">\begin</span><span class="nb">{</span>small<span class="nb">}</span>
</div><div id="l570" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l571" class="code_block">| ?- get<span class="nb">_</span>calls(q(X,Y),Ent,Ret).
</div><div id="l572" class="code_block">
</div><div id="l573" class="code_block">X = a
</div><div id="l574" class="code_block">Y = <span class="nb">_</span>h94
</div><div id="l575" class="code_block">Ent = 136069412
</div><div id="l576" class="code_block">Ret = ret(a,<span class="nb">_</span>h94);
</div><div id="l577" class="code_block">
</div><div id="l578" class="code_block">X = <span class="nb">_</span>h80
</div><div id="l579" class="code_block">Y = c
</div><div id="l580" class="code_block">Ent = 136069444
</div><div id="l581" class="code_block">Ret = ret(<span class="nb">_</span>h80,c);
</div><div id="l582" class="code_block">
</div><div id="l583" class="code_block">X = <span class="nb">_</span>h80
</div><div id="l584" class="code_block">Y = <span class="nb">_</span>h94
</div><div id="l585" class="code_block">Ent = 136043988
</div><div id="l586" class="code_block">Ret = ret(<span class="nb">_</span>h80,<span class="nb">_</span>h94);
</div><div id="l587" class="code_block">
</div><div id="l588" class="code_block">no
</div><div id="l589" class="code_block">| ?- get<span class="nb">_</span>calls(q(a,Y),Ent,Ret).
</div><div id="l590" class="code_block">
</div><div id="l591" class="code_block">Y = <span class="nb">_</span>h88
</div><div id="l592" class="code_block">Ent = 136069412
</div><div id="l593" class="code_block">Ret = ret(a,<span class="nb">_</span>h88);
</div><div id="l594" class="code_block">
</div><div id="l595" class="code_block">Y = c
</div><div id="l596" class="code_block">Ent = 136069444
</div><div id="l597" class="code_block">Ret = ret(a,c);
</div><div id="l598" class="code_block">
</div><div id="l599" class="code_block">Y = <span class="nb">_</span>h88
</div><div id="l600" class="code_block">Ent = 136043988
</div><div id="l601" class="code_block">Ret = ret(a,<span class="nb">_</span>h88);
</div><div id="l602" class="code_block">
</div><div id="l603" class="code_block">no
</div><div id="l604" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l605" class="code_block"><span class="k">\end</span><span class="nb">{</span>small<span class="nb">}</span>
</div><div id="l606" class="code_block"><span class="k">\end</span><span class="nb">{</span>minipage<span class="nb">}</span> <span class="k">\\</span>
</div><div id="l607" class="code_block"><span class="k">\vspace*</span><span class="nb">{</span>-1ex<span class="nb">}</span> <span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l608" class="code_block"><span class="k">\end</span><span class="nb">{</span>tabular<span class="nb">}</span>
</div><div id="l609" class="code_block"><span class="k">\end</span><span class="nb">{</span>tabular<span class="nb">}</span>
</div><div id="l610" class="code_block"><span class="k">\end</span><span class="nb">{</span>example<span class="nb">}</span>
</div><div id="l611" class="code_block"><span class="k">\end</span><span class="nb">{</span>minipage<span class="nb">}</span> <span class="k">\\</span>
</div><div id="l612" class="code_block">
</div><div id="l613" class="code_block"><span class="c">% - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
</div><div id="l614" class="code_block">
</div><div id="l615" class="code_block"><span class="k">\ourstandarditem</span><span class="nb">{</span>get<span class="k">\_calls\_for\_table</span>(+PredSpec,?Call)<span class="nb">}{</span>get<span class="k">\_calls\_for\_table</span>/2<span class="nb">}{</span>Tabling<span class="nb">}</span>
</div><div id="l616" class="code_block"><span class="c">%</span>
</div><div id="l617" class="code_block">Identifies through backtracking all the subgoals whose predicate is
</div><div id="l618" class="code_block">that of <span class="k">\code</span><span class="nb">{</span>PredSpec<span class="nb">}</span> and which unify with <span class="k">\code</span><span class="nb">{</span>Call<span class="nb">}</span>.
</div><div id="l619" class="code_block"><span class="k">\code</span><span class="nb">{</span>PredSpec<span class="nb">}</span> is left unchanged while <span class="k">\code</span><span class="nb">{</span>Call<span class="nb">}</span> contains the
</div><div id="l620" class="code_block">unified resultant.
</div><div id="l621" class="code_block">
</div><div id="l622" class="code_block"><span class="k">\comment</span><span class="nb">{</span>Error if either <span class="k">\code</span><span class="nb">{</span>PredSpec<span class="nb">}</span> is a nontabled pred (STRUCTs
</div><div id="l623" class="code_block">and STRINGs are caught here) or a variable.  Fails if <span class="k">\code</span><span class="nb">{</span>PredSpec<span class="nb">}</span>
</div><div id="l624" class="code_block">is any other type or if <span class="k">\code</span><span class="nb">{</span>Call<span class="nb">}</span> does not unify with any call in
</div><div id="l625" class="code_block">the table.<span class="nb">}</span>
</div><div id="l626" class="code_block">
</div><div id="l627" class="code_block"><span class="k">\begin</span><span class="nb">{</span>minipage<span class="nb">}{</span>6.1in<span class="nb">}</span>
</div><div id="l628" class="code_block"><span class="k">\begin</span><span class="nb">{</span>example<span class="nb">}</span><span class="k">\</span> <span class="k">\\</span>
</div><div id="l629" class="code_block"><span class="k">\\</span>
</div><div id="l630" class="code_block"><span class="k">\hspace*</span><span class="nb">{</span>-0.5em<span class="nb">}</span><span class="k">\begin</span><span class="nb">{</span>tabular<span class="nb">}{</span>l@<span class="nb">{</span><span class="k">\hspace</span><span class="nb">{</span>1.5em<span class="nb">}}</span>r<span class="nb">}</span>
</div><div id="l631" class="code_block"><span class="k">\begin</span><span class="nb">{</span>tabular<span class="nb">}{</span>c<span class="nb">}</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l632" class="code_block"><span class="k">\rule</span><span class="nb">{</span>0ex<span class="nb">}{</span>2.5ex<span class="nb">}</span><span class="k">\textbf</span><span class="nb">{</span>Variant Predicate<span class="nb">}</span> <span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l633" class="code_block"><span class="k">\vspace*</span><span class="nb">{</span>-1ex<span class="nb">}</span> <span class="k">\\</span>
</div><div id="l634" class="code_block"><span class="k">\begin</span><span class="nb">{</span>minipage<span class="nb">}{</span>17.35em<span class="nb">}</span>
</div><div id="l635" class="code_block"><span class="k">\begin</span><span class="nb">{</span>small<span class="nb">}</span>
</div><div id="l636" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l637" class="code_block">|?- get<span class="nb">_</span>calls<span class="nb">_</span>for<span class="nb">_</span>table(p(1,3),Call).  
</div><div id="l638" class="code_block">
</div><div id="l639" class="code_block">Call = p(<span class="nb">_</span>h142,3);
</div><div id="l640" class="code_block">
</div><div id="l641" class="code_block">Call = p(1,<span class="nb">_</span>h143);
</div><div id="l642" class="code_block">
</div><div id="l643" class="code_block">no
</div><div id="l644" class="code_block">| ?- get<span class="nb">_</span>calls<span class="nb">_</span>for<span class="nb">_</span>table(p/2,Call).
</div><div id="l645" class="code_block">
</div><div id="l646" class="code_block">Call = p(<span class="nb">_</span>h137,3);
</div><div id="l647" class="code_block">
</div><div id="l648" class="code_block">Call = p(1,<span class="nb">_</span>h138);
</div><div id="l649" class="code_block">
</div><div id="l650" class="code_block">no
</div><div id="l651" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l652" class="code_block"><span class="k">\end</span><span class="nb">{</span>small<span class="nb">}</span>
</div><div id="l653" class="code_block"><span class="k">\end</span><span class="nb">{</span>minipage<span class="nb">}</span> <span class="k">\\</span>
</div><div id="l654" class="code_block"><span class="k">\vspace*</span><span class="nb">{</span>-1ex<span class="nb">}</span> <span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l655" class="code_block"><span class="k">\end</span><span class="nb">{</span>tabular<span class="nb">}</span>
</div><div id="l656" class="code_block"> <span class="nb">&amp;</span>
</div><div id="l657" class="code_block"><span class="k">\begin</span><span class="nb">{</span>tabular<span class="nb">}{</span>c<span class="nb">}</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l658" class="code_block"><span class="k">\rule</span><span class="nb">{</span>0ex<span class="nb">}{</span>2.5ex<span class="nb">}</span><span class="k">\textbf</span><span class="nb">{</span>Subsumptive Predicate<span class="nb">}</span> <span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l659" class="code_block"><span class="k">\vspace*</span><span class="nb">{</span>-1ex<span class="nb">}</span> <span class="k">\\</span>
</div><div id="l660" class="code_block"><span class="k">\begin</span><span class="nb">{</span>minipage<span class="nb">}{</span>17.85em<span class="nb">}</span>
</div><div id="l661" class="code_block"><span class="k">\begin</span><span class="nb">{</span>small<span class="nb">}</span>
</div><div id="l662" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l663" class="code_block">| ?- get<span class="nb">_</span>calls<span class="nb">_</span>for<span class="nb">_</span>table(q(X,Y),Call). 
</div><div id="l664" class="code_block">
</div><div id="l665" class="code_block">X = <span class="nb">_</span>h80
</div><div id="l666" class="code_block">Y = <span class="nb">_</span>h94
</div><div id="l667" class="code_block">Call = q(a,<span class="nb">_</span>h167);
</div><div id="l668" class="code_block">
</div><div id="l669" class="code_block">X = <span class="nb">_</span>h80
</div><div id="l670" class="code_block">Y = <span class="nb">_</span>h94
</div><div id="l671" class="code_block">Call = q(<span class="nb">_</span>h166,c);
</div><div id="l672" class="code_block">
</div><div id="l673" class="code_block">X = <span class="nb">_</span>h80
</div><div id="l674" class="code_block">Y = <span class="nb">_</span>h94
</div><div id="l675" class="code_block">Call = q(<span class="nb">_</span>h166,<span class="nb">_</span>h167);
</div><div id="l676" class="code_block">
</div><div id="l677" class="code_block">no
</div><div id="l678" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l679" class="code_block"><span class="k">\end</span><span class="nb">{</span>small<span class="nb">}</span>
</div><div id="l680" class="code_block"><span class="k">\end</span><span class="nb">{</span>minipage<span class="nb">}</span> <span class="k">\\</span>
</div><div id="l681" class="code_block"><span class="k">\vspace*</span><span class="nb">{</span>-1ex<span class="nb">}</span> <span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l682" class="code_block"><span class="k">\end</span><span class="nb">{</span>tabular<span class="nb">}</span>
</div><div id="l683" class="code_block"><span class="k">\end</span><span class="nb">{</span>tabular<span class="nb">}</span>
</div><div id="l684" class="code_block"><span class="k">\end</span><span class="nb">{</span>example<span class="nb">}</span>
</div><div id="l685" class="code_block"><span class="k">\end</span><span class="nb">{</span>minipage<span class="nb">}</span> <span class="k">\\</span>
</div><div id="l686" class="code_block">
</div><div id="l687" class="code_block"><span class="k">\comment</span><span class="nb">{</span>
</div><div id="l688" class="code_block">The second example backtracks through all entries in the table, since
</div><div id="l689" class="code_block">only skeletal information is used from the first argument.
</div><div id="l690" class="code_block"><span class="nb">}</span>
</div><div id="l691" class="code_block">
</div><div id="l692" class="code_block"><span class="c">% - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
</div><div id="l693" class="code_block">
</div><div id="l694" class="code_block"><span class="k">\ourstandarditem</span><span class="nb">{</span>get<span class="k">\_returns</span>(+TableEntryHandle,<span class="k">\#</span>ReturnSkeleton)<span class="nb">}{</span>get<span class="k">\_returns</span>/2<span class="nb">}{</span>Tabling<span class="nb">}</span>
</div><div id="l695" class="code_block"><span class="c">%</span>
</div><div id="l696" class="code_block">Backtracks through the answers for the subgoal whose table entry is
</div><div id="l697" class="code_block">referenced through the first argument, <span class="k">\code</span><span class="nb">{</span>TableEntryHandle<span class="nb">}</span>, and
</div><div id="l698" class="code_block">instantiates <span class="k">\code</span><span class="nb">{</span>ReturnSkeleton<span class="nb">}</span> with the variable bindings
</div><div id="l699" class="code_block">corresponding to the return.
</div><div id="l700" class="code_block">
</div><div id="l701" class="code_block">The supplied values for the entry handle and return skeleton should be
</div><div id="l702" class="code_block">obtained from some previous invocation of a table-inspection
</div><div id="l703" class="code_block">predicate.
</div><div id="l704" class="code_block">
</div><div id="l705" class="code_block"><span class="k">\begin</span><span class="nb">{</span>minipage<span class="nb">}{</span>6in<span class="nb">}</span>
</div><div id="l706" class="code_block"><span class="k">\begin</span><span class="nb">{</span>example<span class="nb">}</span><span class="k">\</span> <span class="k">\\</span>
</div><div id="l707" class="code_block"><span class="k">\\</span>
</div><div id="l708" class="code_block"><span class="k">\begin</span><span class="nb">{</span>tabular<span class="nb">}{</span>l@<span class="nb">{</span><span class="k">\hspace</span><span class="nb">{</span>4em<span class="nb">}}</span>r<span class="nb">}</span>
</div><div id="l709" class="code_block"><span class="k">\begin</span><span class="nb">{</span>tabular<span class="nb">}{</span>c<span class="nb">}</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l710" class="code_block"><span class="k">\rule</span><span class="nb">{</span>0ex<span class="nb">}{</span>2.5ex<span class="nb">}</span><span class="k">\textbf</span><span class="nb">{</span>Variant Predicate<span class="nb">}</span> <span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l711" class="code_block"><span class="k">\vspace*</span><span class="nb">{</span>-1ex<span class="nb">}</span> <span class="k">\\</span>
</div><div id="l712" class="code_block"><span class="k">\begin</span><span class="nb">{</span>minipage<span class="nb">}{</span>15em<span class="nb">}</span>
</div><div id="l713" class="code_block"><span class="k">\begin</span><span class="nb">{</span>small<span class="nb">}</span>
</div><div id="l714" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l715" class="code_block">| ?- get<span class="nb">_</span>calls(p(X,3),Ent,Ret),
</div><div id="l716" class="code_block">     get<span class="nb">_</span>returns(Ent,Ret).
</div><div id="l717" class="code_block">
</div><div id="l718" class="code_block">X = 2
</div><div id="l719" class="code_block">Ent = 136039156    <span class="c">% p(X,3)</span>
</div><div id="l720" class="code_block">Ret = ret(2);
</div><div id="l721" class="code_block">
</div><div id="l722" class="code_block">X = 1
</div><div id="l723" class="code_block">Ent = 136039156    
</div><div id="l724" class="code_block">Ret = ret(1);
</div><div id="l725" class="code_block">
</div><div id="l726" class="code_block">X = 1
</div><div id="l727" class="code_block">Ent = 136039108    <span class="c">% p(1,Y)</span>
</div><div id="l728" class="code_block">Ret = ret(3);
</div><div id="l729" class="code_block">
</div><div id="l730" class="code_block">X = 1
</div><div id="l731" class="code_block">Ent = 136039108
</div><div id="l732" class="code_block">Ret = ret(3);
</div><div id="l733" class="code_block">
</div><div id="l734" class="code_block">no
</div><div id="l735" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l736" class="code_block"><span class="k">\end</span><span class="nb">{</span>small<span class="nb">}</span>
</div><div id="l737" class="code_block"><span class="k">\end</span><span class="nb">{</span>minipage<span class="nb">}</span> <span class="k">\\</span>
</div><div id="l738" class="code_block"><span class="k">\vspace*</span><span class="nb">{</span>-1ex<span class="nb">}</span> <span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l739" class="code_block"><span class="k">\end</span><span class="nb">{</span>tabular<span class="nb">}</span>
</div><div id="l740" class="code_block"> <span class="nb">&amp;</span>
</div><div id="l741" class="code_block"><span class="k">\begin</span><span class="nb">{</span>tabular<span class="nb">}{</span>c<span class="nb">}</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l742" class="code_block"><span class="k">\rule</span><span class="nb">{</span>0ex<span class="nb">}{</span>2.5ex<span class="nb">}</span><span class="k">\textbf</span><span class="nb">{</span>Subsumptive Predicate<span class="nb">}</span> <span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l743" class="code_block"><span class="k">\vspace*</span><span class="nb">{</span>-1ex<span class="nb">}</span> <span class="k">\\</span>
</div><div id="l744" class="code_block"><span class="k">\begin</span><span class="nb">{</span>minipage<span class="nb">}{</span>15em<span class="nb">}</span>
</div><div id="l745" class="code_block"><span class="k">\begin</span><span class="nb">{</span>small<span class="nb">}</span>
</div><div id="l746" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l747" class="code_block">| ?- get<span class="nb">_</span>calls(q(a,c),Ent,Ret),
</div><div id="l748" class="code_block">     get<span class="nb">_</span>returns(Ent,Ret).
</div><div id="l749" class="code_block">
</div><div id="l750" class="code_block">Ent = 136069412    <span class="c">% q(a,Y)</span>
</div><div id="l751" class="code_block">Ret = ret(a,c);
</div><div id="l752" class="code_block">
</div><div id="l753" class="code_block">Ent = 136069444    <span class="c">% q(X,c)</span>
</div><div id="l754" class="code_block">Ret = ret(a,c);
</div><div id="l755" class="code_block">
</div><div id="l756" class="code_block">Ent = 136043988    <span class="c">% q(X,Y)</span>
</div><div id="l757" class="code_block">Ret = ret(a,c);
</div><div id="l758" class="code_block">
</div><div id="l759" class="code_block">no
</div><div id="l760" class="code_block">| ?- get<span class="nb">_</span>calls(q(c,a),Ent,Ret),
</div><div id="l761" class="code_block">     get<span class="nb">_</span>returns(Ent,Ret).
</div><div id="l762" class="code_block">
</div><div id="l763" class="code_block">no
</div><div id="l764" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l765" class="code_block"><span class="k">\end</span><span class="nb">{</span>small<span class="nb">}</span>
</div><div id="l766" class="code_block"><span class="k">\end</span><span class="nb">{</span>minipage<span class="nb">}</span> <span class="k">\\</span>
</div><div id="l767" class="code_block"><span class="k">\vspace*</span><span class="nb">{</span>-1ex<span class="nb">}</span> <span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l768" class="code_block"><span class="k">\end</span><span class="nb">{</span>tabular<span class="nb">}</span>
</div><div id="l769" class="code_block"><span class="k">\end</span><span class="nb">{</span>tabular<span class="nb">}</span>
</div><div id="l770" class="code_block"><span class="k">\end</span><span class="nb">{</span>example<span class="nb">}</span>
</div><div id="l771" class="code_block"><span class="k">\end</span><span class="nb">{</span>minipage<span class="nb">}</span> <span class="k">\\</span>
</div><div id="l772" class="code_block">
</div><div id="l773" class="code_block"><span class="c">% - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
</div><div id="l774" class="code_block">
</div><div id="l775" class="code_block"><span class="k">\ourstandarditem</span><span class="nb">{</span>get<span class="k">\_returns\_and\_tvs</span>(+TableEntryHandle,<span class="k">\#</span>ReturnSkeleton,-TruthValue)<span class="nb">}{</span>get<span class="k">\_returns\_and\_tvs</span>/3<span class="nb">}{</span>Tabling<span class="nb">}</span>
</div><div id="l776" class="code_block"><span class="c">%</span>
</div><div id="l777" class="code_block">Identical to <span class="k">\code</span><span class="nb">{</span>get<span class="k">\_returns</span>/2<span class="nb">}</span>, but also obtains the truth value
</div><div id="l778" class="code_block">of a given answer, setting <span class="nb">{</span><span class="k">\tt</span> TruthValue<span class="nb">}</span> to <span class="nb">{</span><span class="k">\tt</span> t<span class="nb">}</span> if the answer
</div><div id="l779" class="code_block">is unconditional and to <span class="nb">{</span><span class="k">\tt</span> u<span class="nb">}</span> if it is conditional.  If a
</div><div id="l780" class="code_block">conditional answer has multiple delay lists, this predicate will
</div><div id="l781" class="code_block">succeed only once, so that using this predicate may be more efficient
</div><div id="l782" class="code_block">than <span class="nb">{</span><span class="k">\tt</span> get<span class="k">\_residual</span>/2<span class="nb">}</span> (although less informative).
</div><div id="l783" class="code_block">
</div><div id="l784" class="code_block"><span class="c">% - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
</div><div id="l785" class="code_block">
</div><div id="l786" class="code_block"><span class="k">\ourstandarditem</span><span class="nb">{</span>get<span class="k">\_returns</span>(+TableEntryHandle,<span class="k">\#</span>ReturnSkeleton,-ReturnHandle)<span class="nb">}{</span>get<span class="k">\_returns</span>/3<span class="nb">}{</span>Tabling<span class="nb">}</span>
</div><div id="l787" class="code_block"><span class="c">%</span>
</div><div id="l788" class="code_block">Functions identically to <span class="k">\code</span><span class="nb">{</span>get<span class="k">\_returns</span>/2<span class="nb">}</span>, but also obtains a
</div><div id="l789" class="code_block">handle to the return given in the second argument.
</div><div id="l790" class="code_block">
</div><div id="l791" class="code_block"><span class="c">% - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
</div><div id="l792" class="code_block">
</div><div id="l793" class="code_block"><span class="k">\ourstandarditem</span><span class="nb">{</span>get<span class="k">\_returns\_for\_call</span>(+CallTerm,?AnswerTerm)<span class="nb">}{</span>get<span class="k">\_returns\_for\_call</span>/2<span class="nb">}{</span>Tabling<span class="nb">}</span>
</div><div id="l794" class="code_block"><span class="c">%</span>
</div><div id="l795" class="code_block">Succeeds through backtracking for each answer of the subgoal
</div><div id="l796" class="code_block"><span class="k">\code</span><span class="nb">{</span>CallTerm<span class="nb">}</span> which unifies with <span class="k">\code</span><span class="nb">{</span>AnswerTerm<span class="nb">}</span>.  Fails if
</div><div id="l797" class="code_block"><span class="k">\code</span><span class="nb">{</span>CallTerm<span class="nb">}</span> is not a subgoal in the table or <span class="k">\code</span><span class="nb">{</span>AnswerTerm<span class="nb">}</span>
</div><div id="l798" class="code_block">does not unify with any of its answers or the answer set is empty.
</div><div id="l799" class="code_block">
</div><div id="l800" class="code_block">The answer is created in its entirety, including fresh variables; the
</div><div id="l801" class="code_block">call is <span class="k">\emph</span><span class="nb">{</span>not<span class="nb">}</span> further instantiated.  However, an explicit
</div><div id="l802" class="code_block">unification of the call with its answer may be performed if so
</div><div id="l803" class="code_block">desired.
</div><div id="l804" class="code_block">
</div><div id="l805" class="code_block"><span class="k">\comment</span><span class="nb">{</span>Fails or gives error whenever <span class="k">\code</span><span class="nb">{</span>get<span class="nb">_</span>call/3<span class="nb">}</span> does.<span class="nb">}</span>
</div><div id="l806" class="code_block">
</div><div id="l807" class="code_block"><span class="k">\begin</span><span class="nb">{</span>minipage<span class="nb">}{</span>6.1in<span class="nb">}</span>
</div><div id="l808" class="code_block"><span class="k">\begin</span><span class="nb">{</span>example<span class="nb">}</span><span class="k">\</span> <span class="k">\\</span>
</div><div id="l809" class="code_block"><span class="k">\\</span>
</div><div id="l810" class="code_block"><span class="k">\hspace*</span><span class="nb">{</span>-0.5em<span class="nb">}</span><span class="k">\begin</span><span class="nb">{</span>tabular<span class="nb">}{</span>l@<span class="nb">{</span><span class="k">\hspace</span><span class="nb">{</span>2.5em<span class="nb">}}</span>r<span class="nb">}</span>
</div><div id="l811" class="code_block"><span class="k">\begin</span><span class="nb">{</span>tabular<span class="nb">}{</span>c<span class="nb">}</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l812" class="code_block"><span class="k">\rule</span><span class="nb">{</span>0ex<span class="nb">}{</span>2.5ex<span class="nb">}</span><span class="k">\textbf</span><span class="nb">{</span>Variant Predicate<span class="nb">}</span> <span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l813" class="code_block"><span class="k">\vspace*</span><span class="nb">{</span>-1ex<span class="nb">}</span> <span class="k">\\</span>
</div><div id="l814" class="code_block"><span class="k">\begin</span><span class="nb">{</span>minipage<span class="nb">}{</span>16.5em<span class="nb">}</span>
</div><div id="l815" class="code_block"><span class="k">\begin</span><span class="nb">{</span>small<span class="nb">}</span>
</div><div id="l816" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l817" class="code_block">| ?- get<span class="nb">_</span>returns<span class="nb">_</span>for<span class="nb">_</span>call(p(1,Y),
</div><div id="l818" class="code_block">                          AnsTerm).
</div><div id="l819" class="code_block">
</div><div id="l820" class="code_block">Y = <span class="nb">_</span>h88
</div><div id="l821" class="code_block">AnsTerm = p(1,<span class="nb">_</span>h161);
</div><div id="l822" class="code_block">
</div><div id="l823" class="code_block">Y = <span class="nb">_</span>h88
</div><div id="l824" class="code_block">AnsTerm = p(1,3);
</div><div id="l825" class="code_block">
</div><div id="l826" class="code_block">Y = <span class="nb">_</span>h88
</div><div id="l827" class="code_block">AnsTerm = p(1,2);
</div><div id="l828" class="code_block">
</div><div id="l829" class="code_block">no
</div><div id="l830" class="code_block">| ?- get<span class="nb">_</span>returns<span class="nb">_</span>for<span class="nb">_</span>call(p(X,Y),
</div><div id="l831" class="code_block">                          AnsTerm).
</div><div id="l832" class="code_block">
</div><div id="l833" class="code_block">no
</div><div id="l834" class="code_block">| ?- get<span class="nb">_</span>returns<span class="nb">_</span>for<span class="nb">_</span>call(p(1,2),
</div><div id="l835" class="code_block">                          AnsTerm).
</div><div id="l836" class="code_block">
</div><div id="l837" class="code_block">no
</div><div id="l838" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l839" class="code_block"><span class="k">\end</span><span class="nb">{</span>small<span class="nb">}</span>
</div><div id="l840" class="code_block"><span class="k">\end</span><span class="nb">{</span>minipage<span class="nb">}</span> <span class="k">\\</span>
</div><div id="l841" class="code_block"><span class="k">\vspace*</span><span class="nb">{</span>-1ex<span class="nb">}</span> <span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l842" class="code_block"><span class="k">\end</span><span class="nb">{</span>tabular<span class="nb">}</span>
</div><div id="l843" class="code_block"> <span class="nb">&amp;</span>
</div><div id="l844" class="code_block"><span class="k">\begin</span><span class="nb">{</span>tabular<span class="nb">}{</span>c<span class="nb">}</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l845" class="code_block"><span class="k">\rule</span><span class="nb">{</span>0ex<span class="nb">}{</span>2.5ex<span class="nb">}</span><span class="k">\textbf</span><span class="nb">{</span>Subsumptive Predicate<span class="nb">}</span> <span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l846" class="code_block"><span class="k">\vspace*</span><span class="nb">{</span>-1ex<span class="nb">}</span> <span class="k">\\</span>
</div><div id="l847" class="code_block"><span class="k">\begin</span><span class="nb">{</span>minipage<span class="nb">}{</span>16.5em<span class="nb">}</span>
</div><div id="l848" class="code_block"><span class="k">\begin</span><span class="nb">{</span>small<span class="nb">}</span>
</div><div id="l849" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l850" class="code_block">| ?- get<span class="nb">_</span>returns<span class="nb">_</span>for<span class="nb">_</span>call(q(a,Y),
</div><div id="l851" class="code_block">                          AnsTerm).
</div><div id="l852" class="code_block">
</div><div id="l853" class="code_block">Y = <span class="nb">_</span>h88
</div><div id="l854" class="code_block">AnsTerm = q(a,c);
</div><div id="l855" class="code_block">
</div><div id="l856" class="code_block">Y = <span class="nb">_</span>h88
</div><div id="l857" class="code_block">AnsTerm = q(a,b);
</div><div id="l858" class="code_block">
</div><div id="l859" class="code_block">no
</div><div id="l860" class="code_block">| ?- get<span class="nb">_</span>returns<span class="nb">_</span>for<span class="nb">_</span>call(q(X,c),
</div><div id="l861" class="code_block">                          AnsTerm).
</div><div id="l862" class="code_block">
</div><div id="l863" class="code_block">X = <span class="nb">_</span>h80
</div><div id="l864" class="code_block">AnsTerm = q(b,c);
</div><div id="l865" class="code_block">
</div><div id="l866" class="code_block">X = <span class="nb">_</span>h80
</div><div id="l867" class="code_block">AnsTerm = q(a,c);
</div><div id="l868" class="code_block">
</div><div id="l869" class="code_block">no
</div><div id="l870" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l871" class="code_block"><span class="k">\end</span><span class="nb">{</span>small<span class="nb">}</span>
</div><div id="l872" class="code_block"><span class="k">\end</span><span class="nb">{</span>minipage<span class="nb">}</span> <span class="k">\\</span>
</div><div id="l873" class="code_block"><span class="k">\vspace*</span><span class="nb">{</span>-1ex<span class="nb">}</span> <span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l874" class="code_block"><span class="k">\end</span><span class="nb">{</span>tabular<span class="nb">}</span>
</div><div id="l875" class="code_block"><span class="k">\end</span><span class="nb">{</span>tabular<span class="nb">}</span>
</div><div id="l876" class="code_block"><span class="k">\end</span><span class="nb">{</span>example<span class="nb">}</span>
</div><div id="l877" class="code_block"><span class="k">\end</span><span class="nb">{</span>minipage<span class="nb">}</span> <span class="k">\\</span>
</div><div id="l878" class="code_block">
</div><div id="l879" class="code_block"><span class="c">% - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
</div><div id="l880" class="code_block">
</div><div id="l881" class="code_block"><span class="k">\ourrepeatstandarditem</span><span class="nb">{</span>get<span class="k">\_residual</span>(<span class="k">\#</span>CallTerm,?DelayList)<span class="nb">}{</span>get<span class="k">\_residual</span>/2<span class="nb">}{</span>Tabling<span class="nb">}</span>
</div><div id="l882" class="code_block"><span class="c">%</span>
</div><div id="l883" class="code_block"><span class="k">\ourstandarditem</span><span class="nb">{</span>variant<span class="k">\_get\_residual</span>(<span class="k">\#</span>CallTerm,?DelayList)<span class="nb">}{</span>variant<span class="k">\_get\_residual</span>/2<span class="nb">}{</span>Tabling<span class="nb">}</span>
</div><div id="l884" class="code_block"><span class="c">%</span>
</div><div id="l885" class="code_block"><span class="nb">{</span><span class="k">\tt</span> get<span class="k">\_residual</span>/2<span class="nb">}</span> backtracks through the answer set of each
</div><div id="l886" class="code_block"><span class="k">\emph</span><span class="nb">{</span>completed<span class="nb">}</span> subgoal in the table that unifies with
</div><div id="l887" class="code_block"><span class="k">\code</span><span class="nb">{</span>CallTerm<span class="nb">}</span>.  With each successful unification, this argument is
</div><div id="l888" class="code_block">further instantiated as well as that of the <span class="k">\code</span><span class="nb">{</span>DelayList<span class="nb">}</span>.
</div><div id="l889" class="code_block">
</div><div id="l890" class="code_block"><span class="k">\begin</span><span class="nb">{</span>example<span class="nb">}</span>
</div><div id="l891" class="code_block">For the following program and table
</div><div id="l892" class="code_block">     <span class="k">\begin</span><span class="nb">{</span>center<span class="nb">}</span>
</div><div id="l893" class="code_block">     <span class="k">\begin</span><span class="nb">{</span>tabular<span class="nb">}{</span>cc<span class="nb">}</span>
</div><div id="l894" class="code_block">     <span class="k">\begin</span><span class="nb">{</span>minipage<span class="nb">}{</span>2.1in<span class="nb">}</span>
</div><div id="l895" class="code_block">     <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l896" class="code_block">          :- table p/2. <span class="k">\\</span>
</div><div id="l897" class="code_block">          p(1,2). <span class="k">\\</span>
</div><div id="l898" class="code_block">          p(1,3):- tnot(p(2,3)). <span class="k">\\</span>
</div><div id="l899" class="code_block">          p(2,3):- tnot(p(1,3)). 
</div><div id="l900" class="code_block">     <span class="nb">}</span>
</div><div id="l901" class="code_block">     <span class="k">\end</span><span class="nb">{</span>minipage<span class="nb">}</span>
</div><div id="l902" class="code_block">     <span class="nb">&amp;</span>
</div><div id="l903" class="code_block">     <span class="k">\begin</span><span class="nb">{</span>tabular<span class="nb">}{</span>||l|l||<span class="nb">}</span>   <span class="k">\hline</span>
</div><div id="l904" class="code_block">     <span class="nb">{</span><span class="k">\em</span> Call<span class="nb">}</span>                 <span class="nb">&amp;</span> <span class="nb">{</span><span class="k">\em</span> Returns<span class="nb">}</span> <span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l905" class="code_block">     p(1,X)                     <span class="nb">&amp;</span> p(1,2) <span class="k">\\</span> 
</div><div id="l906" class="code_block">                                <span class="nb">&amp;</span> p(1,3):- tnot(p(2,3)) <span class="k">\\</span> <span class="k">\hline</span>
</div><div id="l907" class="code_block">     p(1,3)                     <span class="nb">&amp;</span> p(1,3):- tnot(p(2,3)) <span class="k">\\</span> <span class="k">\hline</span>
</div><div id="l908" class="code_block">     p(2,3)                     <span class="nb">&amp;</span> p(2,3):- tnot(p(1,3)) <span class="k">\\</span> <span class="k">\hline</span>
</div><div id="l909" class="code_block">     <span class="k">\end</span><span class="nb">{</span>tabular<span class="nb">}</span>
</div><div id="l910" class="code_block">     <span class="k">\end</span><span class="nb">{</span>tabular<span class="nb">}</span>
</div><div id="l911" class="code_block">     <span class="k">\end</span><span class="nb">{</span>center<span class="nb">}</span>
</div><div id="l912" class="code_block">the completed subgoals are <span class="nb">{</span><span class="k">\tt</span> p(1,X)<span class="nb">}</span>, <span class="nb">{</span><span class="k">\tt</span> p(1,3)<span class="nb">}</span>, and <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l913" class="code_block">p(2,3)<span class="nb">}</span>.  Calls to <span class="nb">{</span><span class="k">\tt</span> get<span class="k">\_residual</span>/2<span class="nb">}</span> will act as follows
</div><div id="l914" class="code_block"><span class="c">%</span>
</div><div id="l915" class="code_block"><span class="k">\begin</span><span class="nb">{</span>center<span class="nb">}</span>
</div><div id="l916" class="code_block"><span class="k">\begin</span><span class="nb">{</span>small<span class="nb">}</span>
</div><div id="l917" class="code_block"><span class="c">%\begin{minipage}{2.5in}</span>
</div><div id="l918" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span> 
</div><div id="l919" class="code_block">| ?- get<span class="nb">_</span>residual(p(X,Y),List).
</div><div id="l920" class="code_block">
</div><div id="l921" class="code_block">X = 1       <span class="c">% from subgoal p(1,X)</span>
</div><div id="l922" class="code_block">Y = 2
</div><div id="l923" class="code_block">List = [];
</div><div id="l924" class="code_block">
</div><div id="l925" class="code_block">X = 1       <span class="c">% from subgoal p(1,X)</span>
</div><div id="l926" class="code_block">Y = 3
</div><div id="l927" class="code_block">List = [tnot(p(2,3))];
</div><div id="l928" class="code_block">
</div><div id="l929" class="code_block">X = 1       <span class="c">% from subgoal p(1,3)</span>
</div><div id="l930" class="code_block">Y = 3
</div><div id="l931" class="code_block">List = [tnot(p(2,3))];
</div><div id="l932" class="code_block">
</div><div id="l933" class="code_block">X = 2       <span class="c">% from subgoal p(2,3)</span>
</div><div id="l934" class="code_block">Y = 3
</div><div id="l935" class="code_block">List = [tnot(p(1,3))];
</div><div id="l936" class="code_block">
</div><div id="l937" class="code_block">no
</div><div id="l938" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l939" class="code_block"><span class="c">%\end{minipage}</span>
</div><div id="l940" class="code_block"><span class="k">\end</span><span class="nb">{</span>small<span class="nb">}</span>
</div><div id="l941" class="code_block"><span class="k">\end</span><span class="nb">{</span>center<span class="nb">}</span>
</div><div id="l942" class="code_block"><span class="k">\end</span><span class="nb">{</span>example<span class="nb">}</span>
</div><div id="l943" class="code_block">
</div><div id="l944" class="code_block">Since the delay list of an answer consists of those literals whose
</div><div id="l945" class="code_block">truth value is unknown in the well-founded model of the program (see
</div><div id="l946" class="code_block">Chapter~<span class="k">\ref</span><span class="nb">{</span>chap:TablingOverview<span class="nb">}</span>) <span class="k">\code</span><span class="nb">{</span>get<span class="k">\_residual</span>/2<span class="nb">}</span> is useful
</div><div id="l947" class="code_block">to examin the residual program (e.g. for XASP).
</div><div id="l948" class="code_block">
</div><div id="l949" class="code_block">For other purposes, it may be desired to examine the answers for a
</div><div id="l950" class="code_block">particular call -- not for all calls that unifiy with <span class="nb">{</span><span class="k">\tt</span> CallTerm<span class="nb">}</span>.
</div><div id="l951" class="code_block">In this case, <span class="nb">{</span><span class="k">\tt</span> variant<span class="k">\_get\_residual</span>/2<span class="nb">}</span> can be used, which
</div><div id="l952" class="code_block">backtracks through all answers for <span class="nb">{</span><span class="k">\tt</span> CallTerm<span class="nb">}</span> if <span class="nb">{</span><span class="k">\tt</span> CallTerm<span class="nb">}</span> is
</div><div id="l953" class="code_block">a tabled subgoal with answers, and fails otherwise.  For the above
</div><div id="l954" class="code_block">example, <span class="nb">{</span><span class="k">\tt</span> variant<span class="k">\_get\_residual</span>/2<span class="nb">}</span> behaves as follows:
</div><div id="l955" class="code_block">
</div><div id="l956" class="code_block"><span class="k">\begin</span><span class="nb">{</span>center<span class="nb">}</span>
</div><div id="l957" class="code_block"><span class="k">\begin</span><span class="nb">{</span>small<span class="nb">}</span>
</div><div id="l958" class="code_block"><span class="c">%\begin{minipage}{2.5in}</span>
</div><div id="l959" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span> 
</div><div id="l960" class="code_block">| ?- variant<span class="k">\_get_residual</span>(p(X,Y),List).
</div><div id="l961" class="code_block">
</div><div id="l962" class="code_block">no
</div><div id="l963" class="code_block">| ?- variant<span class="k">\_get_residual</span>(p(1,Y),List).
</div><div id="l964" class="code_block">
</div><div id="l965" class="code_block">X = 1       <span class="c">% from subgoal p(1,X)</span>
</div><div id="l966" class="code_block">Y = 2
</div><div id="l967" class="code_block">List = [];
</div><div id="l968" class="code_block">
</div><div id="l969" class="code_block">X = 1       <span class="c">% from subgoal p(1,X)</span>
</div><div id="l970" class="code_block">Y = 3
</div><div id="l971" class="code_block">List = [tnot(p(2,3))];
</div><div id="l972" class="code_block">
</div><div id="l973" class="code_block">no
</div><div id="l974" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l975" class="code_block"><span class="c">%\end{minipage}</span>
</div><div id="l976" class="code_block"><span class="k">\end</span><span class="nb">{</span>small<span class="nb">}</span>
</div><div id="l977" class="code_block"><span class="k">\end</span><span class="nb">{</span>center<span class="nb">}</span>
</div><div id="l978" class="code_block">
</div><div id="l979" class="code_block"><span class="nb">{</span><span class="k">\bf</span> Error Cases<span class="nb">}</span>
</div><div id="l980" class="code_block"><span class="k">\bi</span>
</div><div id="l981" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> CallTerm<span class="nb">}</span> is not a callable term
</div><div id="l982" class="code_block"><span class="k">\bi</span>
</div><div id="l983" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> type<span class="k">\_error</span>(callable<span class="k">\_term</span>,CallTerm)<span class="nb">}</span>
</div><div id="l984" class="code_block"><span class="k">\ei</span>
</div><div id="l985" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> CallTerm<span class="nb">}</span> does not correspond to a tabled predicate
</div><div id="l986" class="code_block"><span class="k">\bi</span>
</div><div id="l987" class="code_block"><span class="k">\item</span> 	<span class="nb">{</span><span class="k">\tt</span> permission<span class="k">\_error</span>(table access,non-tabled predicate,<span class="nb">{</span><span class="k">\tt</span> CallTerm<span class="nb">}</span>)<span class="nb">}</span>
</div><div id="l988" class="code_block"><span class="k">\ei</span>
</div><div id="l989" class="code_block"><span class="k">\ei</span>
</div><div id="l990" class="code_block">
</div><div id="l991" class="code_block"><span class="c">% - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
</div><div id="l992" class="code_block">
</div><div id="l993" class="code_block"><span class="k">\ourrepeatstandarditem</span><span class="nb">{</span>table<span class="k">\_state</span>(+CallTerm,?PredType,?CallType,?AnsSetStatus)<span class="nb">}{</span>table<span class="k">\_state</span>/1<span class="nb">}{</span>Tabling<span class="nb">}</span>
</div><div id="l994" class="code_block">
</div><div id="l995" class="code_block"><span class="k">\ourstandarditem</span><span class="nb">{</span>table<span class="k">\_state</span>(+TableEntryHandle,?PredType,?CallType,?AnsSetStatus)<span class="nb">}{</span>table<span class="k">\_state</span>/4<span class="nb">}{</span>Tabling<span class="nb">}</span>
</div><div id="l996" class="code_block"><span class="c">%</span>
</div><div id="l997" class="code_block">Succeeds whenever <span class="k">\code</span><span class="nb">{</span>CallTerm<span class="nb">}</span> is a subgoal in the table, or
</div><div id="l998" class="code_block"><span class="k">\code</span><span class="nb">{</span>TableEntryHandle<span class="nb">}</span> is a valid reference to a table entry, and its
</div><div id="l999" class="code_block">predicate type, the type of the call, and the status of its answer
</div><div id="l1000" class="code_block">set, unify with arguments 2 through 4, respectively.
</div><div id="l1001" class="code_block">
</div><div id="l1002" class="code_block">XSB defines three sets of atomic constants, one for each parameter.
</div><div id="l1003" class="code_block">Taken together, they provide a detailed description of the given call.
</div><div id="l1004" class="code_block">The valid combinations and their specific meaning is given in the
</div><div id="l1005" class="code_block">following table.  Notice that not only can these combinations describe
</div><div id="l1006" class="code_block">the characteristics of a subgoal in the table, but they are also
</div><div id="l1007" class="code_block">equipped to predict how a new goal would have been treated had it been
</div><div id="l1008" class="code_block">called at that moment.
</div><div id="l1009" class="code_block">
</div><div id="l1010" class="code_block"><span class="k">\begin</span><span class="nb">{</span>center<span class="nb">}</span>
</div><div id="l1011" class="code_block"><span class="k">\begin</span><span class="nb">{</span>small<span class="nb">}</span>
</div><div id="l1012" class="code_block"><span class="k">\begin</span><span class="nb">{</span>tabular<span class="nb">}{</span>|c|c|l|l|<span class="nb">}</span> <span class="k">\hline</span>
</div><div id="l1013" class="code_block"><span class="k">\code</span><span class="nb">{</span>PredType<span class="nb">}</span> <span class="nb">&amp;</span> <span class="k">\code</span><span class="nb">{</span>CallType<span class="nb">}</span>       <span class="nb">&amp;</span> <span class="k">\code</span><span class="nb">{</span>AnsSetStatus<span class="nb">}</span>
</div><div id="l1014" class="code_block">                <span class="nb">&amp;</span> <span class="k">\multicolumn</span><span class="nb">{</span>1<span class="nb">}{</span>c|<span class="nb">}{</span>Description<span class="nb">}</span> <span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l1015" class="code_block">        <span class="nb">&amp;</span>       <span class="nb">&amp;</span> <span class="k">\code</span><span class="nb">{</span>complete<span class="nb">}</span>       <span class="nb">&amp;</span> Self explanatory. <span class="k">\\</span> <span class="k">\cline</span><span class="nb">{</span>3-4<span class="nb">}</span>
</div><div id="l1016" class="code_block">        <span class="nb">&amp;</span>       <span class="nb">&amp;</span>                       <span class="nb">&amp;</span> An incremental table that has been <span class="k">\\</span>
</div><div id="l1017" class="code_block">        <span class="nb">&amp;</span> <span class="k">\code</span><span class="nb">{</span>producer<span class="nb">}</span>  <span class="nb">&amp;</span> <span class="nb">{</span><span class="k">\code</span><span class="nb">{</span>incremental<span class="k">\_needs\_reeval</span><span class="nb">}}</span> 
</div><div id="l1018" class="code_block">                                        <span class="nb">&amp;</span> invalidated, and is therefore inconsistent <span class="k">\\</span>
</div><div id="l1019" class="code_block">        <span class="nb">&amp;</span>       <span class="nb">&amp;</span>                       <span class="nb">&amp;</span> with a KB and needs recomputation. <span class="k">\\</span> <span class="k">\cline</span><span class="nb">{</span>3-4<span class="nb">}</span>
</div><div id="l1020" class="code_block"><span class="k">\code</span><span class="nb">{</span>variant<span class="nb">}</span>  <span class="nb">&amp;</span>   <span class="nb">&amp;</span> <span class="k">\code</span><span class="nb">{</span>incomplete<span class="nb">}</span>
</div><div id="l1021" class="code_block">                <span class="nb">&amp;</span> Self explanatory. <span class="k">\\</span> <span class="k">\cline</span><span class="nb">{</span>2-4<span class="nb">}</span>
</div><div id="l1022" class="code_block">        <span class="nb">&amp;</span> <span class="k">\code</span><span class="nb">{</span>no<span class="k">\_entry</span><span class="nb">}</span>      <span class="nb">&amp;</span> <span class="k">\code</span><span class="nb">{</span>undefined<span class="nb">}</span>
</div><div id="l1023" class="code_block">                <span class="nb">&amp;</span> The call does not appear in the table. <span class="k">\\</span> <span class="k">\hline</span>
</div><div id="l1024" class="code_block">        <span class="nb">&amp;</span>       <span class="nb">&amp;</span> <span class="k">\code</span><span class="nb">{</span>complete<span class="nb">}</span> <span class="nb">&amp;</span> Self explanatory. <span class="k">\\</span> <span class="k">\cline</span><span class="nb">{</span>3-4<span class="nb">}</span>
</div><div id="l1025" class="code_block">        <span class="nb">&amp;</span> <span class="k">\raisebox</span><span class="nb">{</span>1.5ex<span class="nb">}</span>[0ex]<span class="nb">{</span><span class="k">\code</span><span class="nb">{</span>producer<span class="nb">}}</span>        <span class="nb">&amp;</span> <span class="k">\code</span><span class="nb">{</span>incomplete<span class="nb">}</span>
</div><div id="l1026" class="code_block">                <span class="nb">&amp;</span> Self explanatory. <span class="k">\\</span> <span class="k">\cline</span><span class="nb">{</span>2-4<span class="nb">}</span>
</div><div id="l1027" class="code_block">        <span class="nb">&amp;</span>       <span class="nb">&amp;</span>       <span class="nb">&amp;</span> The call is in the table and is properly <span class="k">\\</span>
</div><div id="l1028" class="code_block">        <span class="nb">&amp;</span>       <span class="nb">&amp;</span> <span class="k">\raisebox</span><span class="nb">{</span>1.5ex<span class="nb">}</span>[0ex]<span class="nb">{</span><span class="k">\code</span><span class="nb">{</span>complete<span class="nb">}}</span>
</div><div id="l1029" class="code_block">                <span class="nb">&amp;</span> subsumed by a completed producer. <span class="k">\\</span> <span class="k">\cline</span><span class="nb">{</span>3-4<span class="nb">}</span>
</div><div id="l1030" class="code_block">        <span class="nb">&amp;</span>  <span class="k">\raisebox</span><span class="nb">{</span>1.5ex<span class="nb">}</span>[0ex]<span class="nb">{</span><span class="k">\code</span><span class="nb">{</span>subsumed<span class="nb">}}</span>
</div><div id="l1031" class="code_block">                <span class="nb">&amp;</span>       <span class="nb">&amp;</span> The call is in the table and is properly <span class="k">\\</span>
</div><div id="l1032" class="code_block">        <span class="nb">&amp;</span>       <span class="nb">&amp;</span> <span class="k">\raisebox</span><span class="nb">{</span>1.5ex<span class="nb">}</span>[0ex]<span class="nb">{</span><span class="k">\code</span><span class="nb">{</span>incomplete<span class="nb">}}</span>
</div><div id="l1033" class="code_block">                <span class="nb">&amp;</span> subsumed by an incomplete producer. <span class="k">\\</span> <span class="k">\cline</span><span class="nb">{</span>2-4<span class="nb">}</span>
</div><div id="l1034" class="code_block">        <span class="nb">&amp;</span>       <span class="nb">&amp;</span>       <span class="nb">&amp;</span> The call is not in the table, but if it were <span class="k">\\</span>
</div><div id="l1035" class="code_block"><span class="k">\code</span><span class="nb">{</span>subsumptive<span class="nb">}</span>      <span class="nb">&amp;</span>       <span class="nb">&amp;</span> <span class="k">\code</span><span class="nb">{</span>complete<span class="nb">}</span>
</div><div id="l1036" class="code_block">                <span class="nb">&amp;</span> to be called, it would consume from a <span class="k">\\</span>
</div><div id="l1037" class="code_block">        <span class="nb">&amp;</span>       <span class="nb">&amp;</span>       <span class="nb">&amp;</span> completed producer. <span class="k">\\</span> <span class="k">\cline</span><span class="nb">{</span>3-4<span class="nb">}</span>
</div><div id="l1038" class="code_block">        <span class="nb">&amp;</span>       <span class="nb">&amp;</span>       <span class="nb">&amp;</span> The call is not in the table, but if it had <span class="k">\\</span>
</div><div id="l1039" class="code_block">        <span class="nb">&amp;</span> <span class="k">\code</span><span class="nb">{</span>no<span class="k">\_entry</span><span class="nb">}</span>      <span class="nb">&amp;</span> <span class="k">\code</span><span class="nb">{</span>incomplete<span class="nb">}</span>
</div><div id="l1040" class="code_block">                <span class="nb">&amp;</span> been called at this moment, it would <span class="k">\\</span>
</div><div id="l1041" class="code_block">        <span class="nb">&amp;</span>       <span class="nb">&amp;</span>       <span class="nb">&amp;</span> consume from an incomplete producer. <span class="k">\\</span> <span class="k">\cline</span><span class="nb">{</span>3-4<span class="nb">}</span>
</div><div id="l1042" class="code_block">        <span class="nb">&amp;</span>       <span class="nb">&amp;</span>       <span class="nb">&amp;</span> The call is not in the table, but if it had <span class="k">\\</span>
</div><div id="l1043" class="code_block">        <span class="nb">&amp;</span>   <span class="nb">&amp;</span> <span class="k">\code</span><span class="nb">{</span>undefined<span class="nb">}</span>   <span class="nb">&amp;</span> been called at this moment, it would be <span class="k">\\</span>
</div><div id="l1044" class="code_block">        <span class="nb">&amp;</span>       <span class="nb">&amp;</span>       <span class="nb">&amp;</span> a producer. <span class="k">\\</span> <span class="k">\hline</span>
</div><div id="l1045" class="code_block"><span class="k">\code</span><span class="nb">{</span>undefined<span class="nb">}</span>        <span class="nb">&amp;</span> <span class="k">\code</span><span class="nb">{</span>undefined<span class="nb">}</span>      <span class="nb">&amp;</span> <span class="k">\code</span><span class="nb">{</span>undefined<span class="nb">}</span>
</div><div id="l1046" class="code_block">                <span class="nb">&amp;</span> The given predicate is not tabled. <span class="k">\\</span> <span class="k">\hline</span>
</div><div id="l1047" class="code_block"><span class="k">\end</span><span class="nb">{</span>tabular<span class="nb">}</span>
</div><div id="l1048" class="code_block"><span class="k">\end</span><span class="nb">{</span>small<span class="nb">}</span>
</div><div id="l1049" class="code_block"><span class="k">\end</span><span class="nb">{</span>center<span class="nb">}</span>
</div><div id="l1050" class="code_block">
</div><div id="l1051" class="code_block"><span class="k">\ourrepeatmoditem</span><span class="nb">{</span>table<span class="k">\_dump</span>(<span class="k">\#</span>Term,+OptionList)<span class="nb">}{</span>table<span class="k">\_dump</span>/2<span class="nb">}{</span>dump<span class="k">\_table</span><span class="nb">}</span>
</div><div id="l1052" class="code_block"><span class="c">%</span>
</div><div id="l1053" class="code_block"><span class="k">\ourmoditem</span><span class="nb">{</span>table<span class="k">\_dump</span>(+Stream,<span class="k">\#</span>Term,+OptionList)<span class="nb">}{</span>table<span class="k">\_dump</span>/3<span class="nb">}{</span>dump<span class="k">\_table</span><span class="nb">}</span>
</div><div id="l1054" class="code_block"><span class="c">%</span>
</div><div id="l1055" class="code_block"><span class="nb">{</span><span class="k">\tt</span> table<span class="k">\_dump</span>/[2,3]<span class="nb">}</span> provides an easy method to view subgoals and
</div><div id="l1056" class="code_block">answers that are present in a table.  Given an input <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span>, <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1057" class="code_block">  table<span class="k">\_dump</span>/[2,3]<span class="nb">}</span> provides information about all tabled subgoals
</div><div id="l1058" class="code_block">that are subsumed by <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span>; if <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> is a variable,
</div><div id="l1059" class="code_block">information is provided about all tables.
</div><div id="l1060" class="code_block">
</div><div id="l1061" class="code_block">The information is provided at three levels of aggregation, and the form
</div><div id="l1062" class="code_block">of the information is determined by the options in <span class="nb">{</span><span class="k">\tt</span> OptionsList<span class="nb">}</span>.
</div><div id="l1063" class="code_block"><span class="c">%</span>
</div><div id="l1064" class="code_block"><span class="k">\begin</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l1065" class="code_block"><span class="k">\item</span> If the option <span class="nb">{</span><span class="k">\tt</span> summary(true)<span class="nb">}</span> is set, the aggregate sum
</div><div id="l1066" class="code_block">  of subgoals and answers that are subsumed by <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> is
</div><div id="l1067" class="code_block">  collected, along with the aggregate sum of calls <span class="nb">{</span><span class="k">\bf</span> to<span class="nb">}</span> these
</div><div id="l1068" class="code_block">  subgoals.  If <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> is a variable this information is broken
</div><div id="l1069" class="code_block">  down by tabled predicates.
</div><div id="l1070" class="code_block"><span class="c">%</span>
</div><div id="l1071" class="code_block"><span class="k">\begin</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l1072" class="code_block"><span class="k">\item</span> If <span class="nb">{</span><span class="k">\tt</span> details(answers)<span class="nb">}</span> is set, a list is collected of every
</div><div id="l1073" class="code_block">  tabled subgoal <span class="s">$</span><span class="nb">S</span><span class="s">$</span> such that <span class="s">$</span><span class="nb">S</span><span class="s">$</span> is subsumed by <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> along
</div><div id="l1074" class="code_block">  with the number of answers for each <span class="s">$</span><span class="nb">S</span><span class="s">$</span> and a list of those answers
</div><div id="l1075" class="code_block">  and the truth value of each answer (<span class="nb">{</span><span class="k">\tt</span> t<span class="nb">}</span> if true and <span class="nb">{</span><span class="k">\tt</span> u<span class="nb">}</span> if
</div><div id="l1076" class="code_block">  undefined).  If <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> is a variable this information is broken
</div><div id="l1077" class="code_block">  down by tabled predicates.
</div><div id="l1078" class="code_block"><span class="c">%</span>
</div><div id="l1079" class="code_block"><span class="k">\item</span> If <span class="nb">{</span><span class="k">\tt</span> details(subgoals)<span class="nb">}</span> is set, a list is collected of all
</div><div id="l1080" class="code_block">  subgoals <span class="s">$</span><span class="nb">S</span><span class="s">$</span> such that <span class="s">$</span><span class="nb">S</span><span class="s">$</span> is subsumed by <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> along with the
</div><div id="l1081" class="code_block">  number of answers for each <span class="s">$</span><span class="nb">S</span><span class="s">$</span>.  However, unlike the action for <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1082" class="code_block">    details(answers)<span class="nb">}</span> the actual list of answers for <span class="s">$</span><span class="nb">S</span><span class="s">$</span> is not
</div><div id="l1083" class="code_block">  returned.  If <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> is a variable this information is broken
</div><div id="l1084" class="code_block">  down by tabled predicates.
</div><div id="l1085" class="code_block"><span class="c">%</span>
</div><div id="l1086" class="code_block"><span class="k">\item</span> If <span class="nb">{</span><span class="k">\tt</span> details(false)<span class="nb">}</span> is set, no detail information is
</div><div id="l1087" class="code_block">  provided for the actual subgoals or their answers.
</div><div id="l1088" class="code_block"><span class="k">\end</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l1089" class="code_block"><span class="c">%</span>
</div><div id="l1090" class="code_block"><span class="k">\item</span> If <span class="nb">{</span><span class="k">\tt</span> OptionsList<span class="nb">}</span> contains the option <span class="nb">{</span><span class="k">\tt</span> results(X)<span class="nb">}</span> for
</div><div id="l1091" class="code_block">  some variable <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span>, <span class="nb">{</span><span class="k">\tt</span> X<span class="nb">}</span> will be instantiated upon
</div><div id="l1092" class="code_block">  backtracking to all infomation collected about the tables.
</div><div id="l1093" class="code_block"><span class="c">%</span>
</div><div id="l1094" class="code_block"><span class="k">\item</span> If the option <span class="nb">{</span><span class="k">\tt</span> output(true)<span class="nb">}</span> is set, the information is
</div><div id="l1095" class="code_block">  written to <span class="nb">{</span><span class="k">\tt</span> Stream<span class="nb">}</span> or to <span class="nb">{</span><span class="k">\tt</span> userout<span class="nb">}</span> in Prolog-readable form.
</div><div id="l1096" class="code_block"><span class="k">\end</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l1097" class="code_block"><span class="c">%</span>
</div><div id="l1098" class="code_block">If not otherwise specified the default options are <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1099" class="code_block">  summary(true)<span class="nb">}</span>, <span class="nb">{</span><span class="k">\tt</span> details(false)<span class="nb">}</span>, <span class="nb">{</span><span class="k">\tt</span> output(true)<span class="nb">}</span>.
</div><div id="l1100" class="code_block">
</div><div id="l1101" class="code_block"><span class="nb">{</span><span class="k">\bf</span> Example<span class="nb">}</span>  Consider the program:
</div><div id="l1102" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1103" class="code_block">:- table p/2.
</div><div id="l1104" class="code_block">p(1,a).
</div><div id="l1105" class="code_block">p(1,b) :- p(2,b).
</div><div id="l1106" class="code_block">p(2,b) :- p(1,a).
</div><div id="l1107" class="code_block">p(3,X) :- q(X).
</div><div id="l1108" class="code_block">
</div><div id="l1109" class="code_block">:- table q/1.
</div><div id="l1110" class="code_block">q(1).              q(2).
</div><div id="l1111" class="code_block">
</div><div id="l1112" class="code_block">:- table r/1.
</div><div id="l1113" class="code_block">r(a).
</div><div id="l1114" class="code_block">
</div><div id="l1115" class="code_block">:- table s/2.
</div><div id="l1116" class="code_block">s(1,a).            s(2,b).           s(1,a1).            s(2,b1).
</div><div id="l1117" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1118" class="code_block">and suppose the top-level query <span class="nb">{</span><span class="k">\tt</span> ?- p(X,Y)<span class="nb">}</span> has been made.  Then
</div><div id="l1119" class="code_block"><span class="nb">{</span><span class="k">\tt</span> table<span class="k">\_dump</span>/2<span class="nb">}</span> provides the following information <span class="nb">{</span><span class="k">\bf</span>
</div><div id="l1120" class="code_block"> (reformatted for readability)<span class="nb">}</span>:
</div><div id="l1121" class="code_block"><span class="c">%</span>
</div><div id="l1122" class="code_block"><span class="nb">{</span><span class="k">\small</span>
</div><div id="l1123" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1124" class="code_block">| ?- table<span class="nb">_</span>dump(<span class="nb">_</span>X,[summary(true)]).
</div><div id="l1125" class="code_block">
</div><div id="l1126" class="code_block">summary = p(A,B) - subgoals(3) - total<span class="nb">_</span>times<span class="nb">_</span>called(4) - total<span class="nb">_</span>answers(7)
</div><div id="l1127" class="code_block">
</div><div id="l1128" class="code_block">X = p(<span class="nb">_</span>h243,<span class="nb">_</span>h244);
</div><div id="l1129" class="code_block">
</div><div id="l1130" class="code_block">summary = q(A) - subgoals(1) - total<span class="nb">_</span>times<span class="nb">_</span>called(1) - total<span class="nb">_</span>answers(2).
</div><div id="l1131" class="code_block">
</div><div id="l1132" class="code_block">X = q(<span class="nb">_</span>h228)
</div><div id="l1133" class="code_block">
</div><div id="l1134" class="code_block">yes
</div><div id="l1135" class="code_block">| ?- table<span class="nb">_</span>dump(<span class="nb">_</span>X,[details(answers)]).
</div><div id="l1136" class="code_block">
</div><div id="l1137" class="code_block">summary = p(A,B) - subgoals(3) - total<span class="nb">_</span>times<span class="nb">_</span>called(4) - total<span class="nb">_</span>answers(7).
</div><div id="l1138" class="code_block">details = p(A,B) - subgoals(3) - details([
</div><div id="l1139" class="code_block">    p(C,D) - times<span class="nb">_</span>called(1) - answers(5) - [p(3,1)-t,p(3,2)-t,p(2,b)-t,p(1,b)-t,p(1,a)-t] 
</div><div id="l1140" class="code_block">                                          - completed,
</div><div id="l1141" class="code_block">    p(1,a) - times<span class="nb">_</span>called(2) - answers(1) - [p(1,a)-t]                         - completed,
</div><div id="l1142" class="code_block">    p(2,b) - times<span class="nb">_</span>called(1) - answers(1) - [p(2,b)-t]                         - completed]).
</div><div id="l1143" class="code_block">
</div><div id="l1144" class="code_block">X = p(<span class="nb">_</span>h232,<span class="nb">_</span>h233);
</div><div id="l1145" class="code_block">
</div><div id="l1146" class="code_block">summary = q(A) - subgoals(1) - total<span class="nb">_</span>times<span class="nb">_</span>called(1) - total<span class="nb">_</span>answers(2).
</div><div id="l1147" class="code_block">details = q(A) - subgoals(1) - details([
</div><div id="l1148" class="code_block">     q(B) - times<span class="nb">_</span>called(1) - answers(2) - [q(2)-t,q(1)-t] - completed]).
</div><div id="l1149" class="code_block">
</div><div id="l1150" class="code_block">X = q(<span class="nb">_</span>h232)
</div><div id="l1151" class="code_block">
</div><div id="l1152" class="code_block">yes
</div><div id="l1153" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1154" class="code_block"><span class="nb">}</span>
</div><div id="l1155" class="code_block">
</div><div id="l1156" class="code_block">As the above example shows, each line of the summary has the form:
</div><div id="l1157" class="code_block">
</div><div id="l1158" class="code_block"><span class="k">\begin</span><span class="nb">{</span>tabbing<span class="nb">}</span>
</div><div id="l1159" class="code_block">fooo<span class="k">\=</span>foo<span class="k">\=</span>foo<span class="k">\=</span>foo<span class="k">\=</span>fooooooooooooooooooooooooooooooo<span class="k">\=</span>ooooooooooooo<span class="k">\=\kill</span>
</div><div id="l1160" class="code_block"><span class="c">%</span>
</div><div id="l1161" class="code_block"><span class="nb">{</span><span class="k">\em</span>   summary = <span class="nb">}</span> <span class="k">\\</span>
</div><div id="l1162" class="code_block"><span class="k">\&gt;</span> <span class="nb">{</span><span class="k">\em</span> Pred/Goal  - subgoals(<span class="s">$</span><span class="nb">N_{subgoals}</span><span class="s">$</span>) - total<span class="k">\_times\_called</span>(<span class="s">$</span><span class="nb">N_{called}</span><span class="s">$</span>) - total<span class="k">\_answers</span>(<span class="s">$</span><span class="nb">N_{answers}</span><span class="s">$</span>)<span class="nb">}</span>
</div><div id="l1163" class="code_block"><span class="c">%</span>
</div><div id="l1164" class="code_block"><span class="k">\end</span><span class="nb">{</span>tabbing<span class="nb">}</span>
</div><div id="l1165" class="code_block">where 
</div><div id="l1166" class="code_block"><span class="k">\bi</span>
</div><div id="l1167" class="code_block"><span class="k">\item</span> <span class="s">$</span><span class="nb">Pred</span><span class="o">/</span><span class="nb">Goal</span><span class="s">$</span> is either a term indicator, if the <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span>
</div><div id="l1168" class="code_block">  argument of <span class="nb">{</span><span class="k">\tt</span> table<span class="k">\_dump</span>/[2,3]<span class="nb">}</span> was a variable (to indicate there
</div><div id="l1169" class="code_block">  should be no filtering of tabled calls); or <span class="nb">{</span><span class="k">\tt</span> Term<span class="nb">}</span> itself.
</div><div id="l1170" class="code_block"><span class="c">%</span>
</div><div id="l1171" class="code_block"><span class="k">\item</span> <span class="s">$</span><span class="nb">N_{subgoals}</span><span class="s">$</span> are the total number tabled subgoals that are
</div><div id="l1172" class="code_block">  subsumed by <span class="s">$</span><span class="nb">Pred</span><span class="o">/</span><span class="nb">Goal</span><span class="s">$</span> (perhaps including <span class="s">$</span><span class="nb">Pred</span><span class="o">/</span><span class="nb">Goal</span><span class="s">$</span> itself).
</div><div id="l1173" class="code_block"><span class="c">%</span>
</div><div id="l1174" class="code_block"><span class="k">\item</span> <span class="s">$</span><span class="nb">N_{called}</span><span class="s">$</span> is the total number of times all subgoals subsumed
</div><div id="l1175" class="code_block">  by <span class="s">$</span><span class="nb">Pred</span><span class="o">/</span><span class="nb">Goal</span><span class="s">$</span> have been called.
</div><div id="l1176" class="code_block"><span class="c">%</span>
</div><div id="l1177" class="code_block"><span class="k">\item</span> <span class="s">$</span><span class="nb">N_{answers}</span><span class="s">$</span> is the total number of answers currently derived
</div><div id="l1178" class="code_block">  by all subgoals subsumed by <span class="s">$</span><span class="nb">Pred</span><span class="o">/</span><span class="nb">Goal</span><span class="s">$</span>.
</div><div id="l1179" class="code_block"><span class="k">\ei</span>
</div><div id="l1180" class="code_block">
</div><div id="l1181" class="code_block">Each line of details has the form:
</div><div id="l1182" class="code_block">
</div><div id="l1183" class="code_block"><span class="k">\begin</span><span class="nb">{</span>tabbing<span class="nb">}</span>
</div><div id="l1184" class="code_block">fooo<span class="k">\=</span>foo<span class="k">\=</span>foo<span class="k">\=</span>foo<span class="k">\=</span>fooooooooooooooooooooooooooooooo<span class="k">\=</span>ooooooooooooo<span class="k">\=\kill</span>
</div><div id="l1185" class="code_block"><span class="c">%</span>
</div><div id="l1186" class="code_block"><span class="nb">{</span><span class="k">\em</span>   Details = <span class="nb">}</span> <span class="k">\\</span>
</div><div id="l1187" class="code_block"><span class="k">\&gt;</span> <span class="nb">{</span><span class="k">\em</span> Pred/Goal  - subgoals(<span class="s">$</span><span class="nb">N_{subgoals}</span><span class="s">$</span>) - details(List)<span class="nb">}</span>
</div><div id="l1188" class="code_block"><span class="c">%</span>
</div><div id="l1189" class="code_block"><span class="k">\end</span><span class="nb">{</span>tabbing<span class="nb">}</span>
</div><div id="l1190" class="code_block"><span class="c">%</span>
</div><div id="l1191" class="code_block">where <span class="nb">{</span><span class="k">\em</span> Pred/Goal<span class="nb">}</span> and <span class="s">$</span><span class="nb">N_{subgoals}</span><span class="s">$</span> are as above.  If <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1192" class="code_block">  details(answers)<span class="nb">}</span> was an input option
</div><div id="l1193" class="code_block"><span class="c">%</span>
</div><div id="l1194" class="code_block"><span class="k">\begin</span><span class="nb">{</span>tabbing<span class="nb">}</span>
</div><div id="l1195" class="code_block">fooo<span class="k">\=</span>foo<span class="k">\=</span>foo<span class="k">\=</span>foo<span class="k">\=</span>fooooooooooooooooooooooooooooooo<span class="k">\=</span>ooooooooooooo<span class="k">\=\kill</span>
</div><div id="l1196" class="code_block"><span class="c">%</span>
</div><div id="l1197" class="code_block"><span class="nb">{</span><span class="k">\em</span> List = <span class="nb">}</span><span class="k">\\</span>
</div><div id="l1198" class="code_block"><span class="k">\&gt;</span>  <span class="nb">{</span><span class="k">\em</span> Subgoal - times<span class="k">\_called</span>(<span class="s">$</span><span class="nb">N_{called}</span><span class="s">$</span>) - answers(<span class="s">$</span><span class="nb">N_{answers}</span><span class="s">$</span>) - List<span class="k">\_of\_Answers</span> - Status<span class="nb">}</span>
</div><div id="l1199" class="code_block"><span class="c">%</span>
</div><div id="l1200" class="code_block"><span class="k">\end</span><span class="nb">{</span>tabbing<span class="nb">}</span>
</div><div id="l1201" class="code_block"><span class="c">%</span>
</div><div id="l1202" class="code_block">for each <span class="s">$</span><span class="nb">Subgoal</span><span class="s">$</span> in the table subsumed by <span class="s">$</span><span class="nb">Pred</span><span class="o">/</span><span class="nb">Goal</span><span class="s">$</span>.  <span class="s">$</span><span class="nb">N_{called}</span><span class="s">$</span>
</div><div id="l1203" class="code_block">and <span class="s">$</span><span class="nb">N_{answers}</span><span class="s">$</span> are as above, while <span class="nb">{</span><span class="k">\em</span> List<span class="k">\_of\_Answers</span><span class="nb">}</span> contains
</div><div id="l1204" class="code_block"><span class="s">$</span><span class="nb">A</span><span class="o">-</span><span class="nb">TV</span><span class="s">$</span> for each answer <span class="s">$</span><span class="nb">A</span><span class="s">$</span> with truth value <span class="s">$</span><span class="nb">TV</span><span class="s">$</span> that is currently
</div><div id="l1205" class="code_block">derived for <span class="s">$</span><span class="nb">Subgoal</span><span class="s">$</span>.  On the other hand, if <span class="nb">{</span><span class="k">\tt</span> details(subgoals)<span class="nb">}</span>
</div><div id="l1206" class="code_block">was an input option
</div><div id="l1207" class="code_block"><span class="k">\begin</span><span class="nb">{</span>tabbing<span class="nb">}</span>
</div><div id="l1208" class="code_block">fooo<span class="k">\=</span>foo<span class="k">\=</span>foo<span class="k">\=</span>foo<span class="k">\=</span>fooooooooooooooooooooooooooooooo<span class="k">\=</span>ooooooooooooo<span class="k">\=\kill</span>
</div><div id="l1209" class="code_block"><span class="c">%</span>
</div><div id="l1210" class="code_block"><span class="nb">{</span><span class="k">\em</span> List = <span class="nb">}</span><span class="k">\\</span>
</div><div id="l1211" class="code_block"><span class="k">\&gt;</span>  <span class="nb">{</span><span class="k">\em</span> Subgoal - times<span class="k">\_called</span>(<span class="s">$</span><span class="nb">N_{called}</span><span class="s">$</span>) - answers(<span class="s">$</span><span class="nb">N_{answers}</span><span class="s">$</span>) - Status<span class="nb">}</span>
</div><div id="l1212" class="code_block"><span class="c">%</span>
</div><div id="l1213" class="code_block"><span class="k">\end</span><span class="nb">{</span>tabbing<span class="nb">}</span>
</div><div id="l1214" class="code_block"><span class="c">%</span>
</div><div id="l1215" class="code_block">where all elements are as before.  Finally <span class="s">$</span><span class="nb">Status</span><span class="s">$</span> is
</div><div id="l1216" class="code_block"><span class="c">%</span>
</div><div id="l1217" class="code_block"><span class="k">\bi</span>
</div><div id="l1218" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> completed<span class="nb">}</span> if <span class="s">$</span><span class="nb">Subgoal</span><span class="s">$</span> has been completed; and
</div><div id="l1219" class="code_block"><span class="c">%</span>
</div><div id="l1220" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> scc(<span class="s">$</span><span class="nb">N_{SCC}</span><span class="s">$</span><span class="nb">}</span>) if <span class="s">$</span><span class="nb">Subgoal</span><span class="s">$</span> is incomplete.  <span class="s">$</span><span class="nb">N_{SCC}</span><span class="s">$</span> is
</div><div id="l1221" class="code_block">  relative: if <span class="s">$</span><span class="nb">N_{SCC}</span><span class="s">$</span> is greater than <span class="s">$</span><span class="nb">M_{SCC}</span><span class="s">$</span> then <span class="s">$</span><span class="nb">N_{SCC}</span><span class="s">$</span> is a
</div><div id="l1222" class="code_block">  descendent of <span class="s">$</span><span class="nb">M_{SCC}</span><span class="s">$</span>: i.e., subgoals in SCC <span class="s">$</span><span class="nb">M_{SCC}</span><span class="s">$</span> depend on
</div><div id="l1223" class="code_block">  subgoals in SCC <span class="s">$</span><span class="nb">N_{SCC}</span><span class="s">$</span>.  However, these numbers should only be
</div><div id="l1224" class="code_block">  used relatively: at a given state in the computation there may be
</div><div id="l1225" class="code_block">  fewer than <span class="s">$</span><span class="nb">M_{SCC}</span><span class="s">$</span> Sccs~<span class="k">\footnote</span><span class="nb">{</span>XSB keeps track of SCCs through
</div><div id="l1226" class="code_block">    an algorithm similar to depth-first search: the numbers associated
</div><div id="l1227" class="code_block">    with subgoals are the depth-first numbers of the minimal
</div><div id="l1228" class="code_block">    back-dependency of a subgoal (cf.~<span class="k">\cite</span><span class="nb">{</span>SaSw98<span class="nb">}</span>)<span class="nb">}</span>.
</div><div id="l1229" class="code_block"><span class="k">\ei</span>
</div><div id="l1230" class="code_block">
</div><div id="l1231" class="code_block">
</div><div id="l1232" class="code_block"><span class="nb">{</span><span class="k">\bf</span> Error Cases<span class="nb">}</span>
</div><div id="l1233" class="code_block"><span class="k">\bi</span>
</div><div id="l1234" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> OptionList<span class="nb">}</span> is a variable, or contains a variable as an element
</div><div id="l1235" class="code_block"><span class="k">\bi</span>
</div><div id="l1236" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> instantiation<span class="k">\_error</span><span class="nb">}</span>
</div><div id="l1237" class="code_block"><span class="k">\ei</span>
</div><div id="l1238" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> OptionList<span class="nb">}</span> is not a list
</div><div id="l1239" class="code_block"><span class="k">\bi</span>
</div><div id="l1240" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> type<span class="k">\_error</span>(list,OptionList)<span class="nb">}</span>
</div><div id="l1241" class="code_block"><span class="k">\ei</span>
</div><div id="l1242" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> OptionList<span class="nb">}</span> contains an element, <span class="nb">{</span><span class="k">\tt</span> O<span class="nb">}</span>, that is not a
</div><div id="l1243" class="code_block">  valid <span class="nb">{</span><span class="k">\tt</span> table<span class="k">\_dump\_option</span><span class="nb">}</span>.
</div><div id="l1244" class="code_block"><span class="k">\bi</span>
</div><div id="l1245" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> domain<span class="k">\_error</span>(table<span class="k">\_dump\_option</span>,O)<span class="nb">}</span>
</div><div id="l1246" class="code_block"><span class="k">\ei</span>
</div><div id="l1247" class="code_block"><span class="k">\ei</span>
</div><div id="l1248" class="code_block">
</div><div id="l1249" class="code_block"><span class="c">%\ourrepeatmoditem{print\_incomplete\_tables(+Stream\_or\_alias)}{print\_incomplete\_tables/1}{tables}</span>
</div><div id="l1250" class="code_block"><span class="k">\ourmoditem</span><span class="nb">{</span>print<span class="k">\_incomplete\_tables</span><span class="nb">}{</span>print<span class="k">\_incomplete\_tables</span>/0<span class="nb">}{</span>tables<span class="nb">}</span>
</div><div id="l1251" class="code_block"><span class="c">%</span>
</div><div id="l1252" class="code_block">These predicates, which can be useful for debugging purposes, print
</div><div id="l1253" class="code_block">out each incomplete subgoal in the current state, followed by the
</div><div id="l1254" class="code_block">ordinal number of the SCC to which that subgoal belongs.  This
</div><div id="l1255" class="code_block">information describes the dependencies among tabled predicates.  In
</div><div id="l1256" class="code_block">local evaluation (the default evaluation method for XSB) all subgoals
</div><div id="l1257" class="code_block">in SCC <span class="s">$</span><span class="nb">m</span><span class="s">$</span> depend on all subgoals in SCC <span class="s">$</span><span class="nb">n</span><span class="s">$</span> if <span class="s">$</span><span class="nb">m &lt; n</span><span class="s">$</span>.  Furthermore,
</div><div id="l1258" class="code_block">all subgoals in a given SCC depend on one another~<span class="k">\footnote</span><span class="nb">{</span>This
</div><div id="l1259" class="code_block">  assumes that there is no early completion, which can remove
</div><div id="l1260" class="code_block">  dependencies. In batched evaluation, the dependencies are less exact
</div><div id="l1261" class="code_block">  -- see <span class="k">\cite</span><span class="nb">{</span>SaSw98<span class="nb">}</span> for details, as SCCs represent a dag of
</div><div id="l1262" class="code_block">  dependencies rather than a chain as in local evaluation.<span class="nb">}</span>.  As its
</div><div id="l1263" class="code_block">name implies, <span class="nb">{</span><span class="k">\tt</span> print<span class="k">\_incomplete\_tables</span>/[0,1]<span class="nb">}</span> print out SCC
</div><div id="l1264" class="code_block">information only for incomplete tables; for full information about the
</div><div id="l1265" class="code_block">SCCs of a computation, forest logging must be used
</div><div id="l1266" class="code_block">(cf. Section~<span class="k">\ref</span><span class="nb">{</span>sec:forest-trace<span class="nb">}</span>).
</div><div id="l1267" class="code_block">
</div><div id="l1268" class="code_block">In <span class="nb">{</span><span class="k">\tt</span> print<span class="k">\_incomplete\_tables</span>/0<span class="nb">}</span>, the information is output to
</div><div id="l1269" class="code_block"><span class="nb">{</span><span class="k">\tt</span> stdout<span class="nb">}</span>.
</div><div id="l1270" class="code_block">
</div><div id="l1271" class="code_block"><span class="nb">{</span><span class="k">\bf</span> Example:<span class="nb">}</span> For the program
</div><div id="l1272" class="code_block"><span class="c">%</span>
</div><div id="l1273" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1274" class="code_block">:- table q/2.
</div><div id="l1275" class="code_block">q(0,<span class="nb">_</span>):- !,print<span class="nb">_</span>incomplete<span class="nb">_</span>tables.
</div><div id="l1276" class="code_block">q(3,A):- q(5,A).
</div><div id="l1277" class="code_block">q(N,A):- N1 is N - 1,q(N1,A).
</div><div id="l1278" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1279" class="code_block">the goal <span class="nb">{</span><span class="k">\tt</span> ?- q(5,foo)<span class="nb">}</span> will produce the output 
</div><div id="l1280" class="code_block"><span class="c">%</span>
</div><div id="l1281" class="code_block"><span class="nb">{</span><span class="k">\small</span>
</div><div id="l1282" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1283" class="code_block">q(5, foo)- scc(1).
</div><div id="l1284" class="code_block">q(4, foo)- scc(1).
</div><div id="l1285" class="code_block">q(3, foo)- scc(1).
</div><div id="l1286" class="code_block">q(2, foo)- scc(2).
</div><div id="l1287" class="code_block">q(1, foo)- scc(3).
</div><div id="l1288" class="code_block">q(0, foo)- scc(4).
</div><div id="l1289" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1290" class="code_block"><span class="nb">}</span>
</div><div id="l1291" class="code_block"><span class="c">%</span>
</div><div id="l1292" class="code_block"><span class="c">%{\bf Error Cases ({\tt print\_incomplete\_tables/1})}</span>
</div><div id="l1293" class="code_block"><span class="c">%\bi</span>
</div><div id="l1294" class="code_block"><span class="c">%\item 	{\tt Stream\_or\_alias} is a variable</span>
</div><div id="l1295" class="code_block"><span class="c">%\bi</span>
</div><div id="l1296" class="code_block"><span class="c">%\item {\tt instantiation\_error}</span>
</div><div id="l1297" class="code_block"><span class="c">%\ei</span>
</div><div id="l1298" class="code_block"><span class="c">%\item {\tt Stream\_or\_alias} is neither a variable, nor a stream term</span>
</div><div id="l1299" class="code_block"><span class="c">%  nor an alias.  </span>
</div><div id="l1300" class="code_block"><span class="c">%\bi</span>
</div><div id="l1301" class="code_block"><span class="c">%\item 	{\tt domain\_error(stream\_or\_alias,Stream\_or\_alias)}</span>
</div><div id="l1302" class="code_block"><span class="c">%\ei</span>
</div><div id="l1303" class="code_block"><span class="c">%\item 	{\tt Stream\_or\_alias} is not associated with an open stream</span>
</div><div id="l1304" class="code_block"><span class="c">%\bi</span>
</div><div id="l1305" class="code_block"><span class="c">%\item 	{\tt existence\_error(stream,Stream\_or\_alias)}</span>
</div><div id="l1306" class="code_block"><span class="c">%\ei</span>
</div><div id="l1307" class="code_block"><span class="c">%\ei</span>
</div><div id="l1308" class="code_block">
</div><div id="l1309" class="code_block"><span class="k">\index</span><span class="nb">{</span>Prolog flags!<span class="nb">{</span><span class="k">\tt</span> exception<span class="k">\_pre\_action</span><span class="nb">}}</span>
</div><div id="l1310" class="code_block"><span class="k">\index</span><span class="nb">{</span>strongly connected components (SCCs)<span class="nb">}</span>
</div><div id="l1311" class="code_block"><span class="k">\index</span><span class="nb">{</span>tabling!and exceptions<span class="nb">}</span>
</div><div id="l1312" class="code_block"><span class="k">\ourmoditem</span><span class="nb">{</span>get<span class="k">\_scc\_dumpfile</span>(-Filename)<span class="nb">}{</span>get<span class="k">\_scc\_dumpfile</span>/1<span class="nb">}{</span>tables<span class="nb">}</span>
</div><div id="l1313" class="code_block"><span class="c">%</span>
</div><div id="l1314" class="code_block">If the Prolog flag <span class="nb">{</span><span class="k">\tt</span> exception<span class="k">\_pre\_action</span><span class="nb">}</span> is set to <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1315" class="code_block">  print<span class="k">\_incomplete\_tables</span><span class="nb">}</span> (its default setting is <span class="nb">{</span><span class="k">\tt</span> none<span class="nb">}</span>), then
</div><div id="l1316" class="code_block">when an exception is thrown, incomplete tables and their SCC
</div><div id="l1317" class="code_block">information are printed to a ``SCC dumpfile&#39;&#39; via <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1318" class="code_block">  print<span class="k">\_incomplete\_tables</span>/1<span class="nb">}</span>.  (No file is generated unless
</div><div id="l1319" class="code_block">  the exception is thrown over at least one incomplete table.)
</div><div id="l1320" class="code_block">
</div><div id="l1321" class="code_block">This predicate returns the name of the last such file generated and
</div><div id="l1322" class="code_block">fails if there is no such file.  Files are written to the <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1323" class="code_block">  <span class="k">\$</span>XSBDIR/etc<span class="nb">}</span> directory with the prefix <span class="nb">{</span><span class="k">\tt</span> scc<span class="k">\_dump\_</span><span class="nb">}</span>.  Users
</div><div id="l1324" class="code_block">are responsible for removing these files.
</div><div id="l1325" class="code_block">
</div><div id="l1326" class="code_block">Note that XSB backtraces (Section~<span class="k">\ref</span><span class="nb">{</span>sec:backtrace<span class="nb">}</span>) provide
</div><div id="l1327" class="code_block">information about the context in which an exception is thrown, but the
</div><div id="l1328" class="code_block">SCC dumpfile provides explicit SCC information along with parameter
</div><div id="l1329" class="code_block">values for tabled predicates.
</div><div id="l1330" class="code_block">
</div><div id="l1331" class="code_block"><span class="nb">{</span><span class="k">\bf</span> Error Cases<span class="nb">}</span>
</div><div id="l1332" class="code_block"><span class="k">\bi</span>
</div><div id="l1333" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> Filename<span class="nb">}</span> is a not a variable
</div><div id="l1334" class="code_block"><span class="k">\bi</span>
</div><div id="l1335" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> instantiation<span class="k">\_error</span><span class="nb">}</span>
</div><div id="l1336" class="code_block"><span class="k">\ei</span>
</div><div id="l1337" class="code_block"><span class="k">\ei</span>
</div><div id="l1338" class="code_block">
</div><div id="l1339" class="code_block"><span class="k">\ourmoditem</span><span class="nb">{</span>explain<span class="k">\_u\_val</span>(+Answer,?Reason,?Type)<span class="nb">}{</span>explain<span class="k">\_u\_value</span>/3<span class="nb">}{</span>tables<span class="nb">}</span>
</div><div id="l1340" class="code_block"><span class="c">%</span>
</div><div id="l1341" class="code_block"><span class="nb">{</span><span class="k">\tt</span> explain<span class="k">\_u\_val</span>/3<span class="nb">}</span> can be used to query why <span class="nb">{</span><span class="k">\tt</span> Answer<span class="nb">}</span> is
</div><div id="l1342" class="code_block">undefined.  <span class="nb">{</span><span class="k">\tt</span> Reason<span class="nb">}</span> may be either <span class="nb">{</span><span class="k">\tt</span> bounded<span class="k">\_rationality</span><span class="nb">}</span> or
</div><div id="l1343" class="code_block"><span class="nb">{</span><span class="k">\tt</span> negative<span class="k">\_loops</span><span class="nb">}</span>.  <span class="nb">{</span><span class="k">\tt</span> Type<span class="nb">}</span> may be either <span class="nb">{</span><span class="k">\tt</span> direct<span class="nb">}</span> or <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1344" class="code_block">  indirect<span class="nb">}</span>.  <span class="nb">{</span><span class="k">\tt</span> bounded<span class="k">\_rationality</span><span class="nb">}</span> is considered direct if <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1345" class="code_block">  Answer<span class="nb">}</span> itself has been abstracted; otherwise it is indirect.  <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1346" class="code_block">  negative<span class="k">\_loops</span><span class="nb">}</span> is considered direct if <span class="nb">{</span><span class="k">\tt</span> Answer<span class="nb">}</span> is involved in
</div><div id="l1347" class="code_block">a loop through negation based on delay dependencies; otherwise it is
</div><div id="l1348" class="code_block">considered direct.  Thus, the predicate may succeed for more than one
</div><div id="l1349" class="code_block">reason, but for each reason there is at most one type,
</div><div id="l1350" class="code_block">
</div><div id="l1351" class="code_block"><span class="k">\begin</span><span class="nb">{</span>example<span class="nb">}</span> <span class="k">\rm</span>
</div><div id="l1352" class="code_block">After executing the query <span class="nb">{</span><span class="k">\tt</span> m<span class="nb">}</span> to the program
</div><div id="l1353" class="code_block"><span class="c">%</span>
</div><div id="l1354" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1355" class="code_block">:- table m/0, p/0, q/0, r/0, s/1.
</div><div id="l1356" class="code_block">m:- p.
</div><div id="l1357" class="code_block">
</div><div id="l1358" class="code_block">p:- q,tnot p.                 p:- s(f(f(f(f(0))))).
</div><div id="l1359" class="code_block">
</div><div id="l1360" class="code_block">q:- tnot r.                   r:- tnot q.
</div><div id="l1361" class="code_block">
</div><div id="l1362" class="code_block">s(f(X)):- s(X).               s(0).
</div><div id="l1363" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1364" class="code_block"><span class="c">%</span>
</div><div id="l1365" class="code_block">where the bounded rationality depth has been set to 3.  the query <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1366" class="code_block"> explain<span class="k">\_u\_value</span>(p,Reason,Type)<span class="nb">}</span> will bind <span class="nb">{</span><span class="k">\tt</span> Reason<span class="nb">}</span> to <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1367" class="code_block"> negative<span class="k">\_loops</span><span class="nb">}</span> and <span class="nb">{</span><span class="k">\tt</span> Type<span class="nb">}</span> to <span class="nb">{</span><span class="k">\tt</span> direct<span class="nb">}</span> and also <span class="nb">{</span><span class="k">\tt</span> Reason<span class="nb">}</span>
</div><div id="l1368" class="code_block"> to <span class="nb">{</span><span class="k">\tt</span> bounded<span class="k">\_rationality</span><span class="nb">}</span> and <span class="nb">{</span><span class="k">\tt</span> Type<span class="nb">}</span> to <span class="nb">{</span><span class="k">\tt</span> indirect<span class="nb">}</span>.  Note
</div><div id="l1369" class="code_block"> that <span class="nb">{</span><span class="k">\tt</span> p<span class="nb">}</span> also indirectly depends on <span class="nb">{</span><span class="k">\tt</span> q<span class="nb">}</span> which is itself
</div><div id="l1370" class="code_block"> involved in a loop through negation.
</div><div id="l1371" class="code_block"><span class="k">\end</span><span class="nb">{</span>example<span class="nb">}</span>
</div><div id="l1372" class="code_block">
</div><div id="l1373" class="code_block">
</div><div id="l1374" class="code_block">
</div><div id="l1375" class="code_block"><span class="c">% - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
</div><div id="l1376" class="code_block">
</div><div id="l1377" class="code_block"><span class="k">\comment</span><span class="nb">{</span>
</div><div id="l1378" class="code_block"><span class="c">%\ournewitem{table\_state(+CallTerm,?State)}{Tabling}</span>
</div><div id="l1379" class="code_block"><span class="c">%\index{\texttt{table\_state/2}}</span>
</div><div id="l1380" class="code_block"><span class="c">%</span>
</div><div id="l1381" class="code_block"><span class="c">%Functions similarly to, and is superseded by, \code{table\_state/4}.</span>
</div><div id="l1382" class="code_block"><span class="c">%The value of \code{State} may be one of the following atoms with the</span>
</div><div id="l1383" class="code_block"><span class="c">%given meaning.</span>
</div><div id="l1384" class="code_block"><span class="c">%</span>
</div><div id="l1385" class="code_block"><span class="c">%\begin{description}</span>
</div><div id="l1386" class="code_block"><span class="c">%\item[{\tt not\_yet\_called}] iff the predicate corresponding to</span>
</div><div id="l1387" class="code_block"><span class="c">%Call has been declared tabled, but there is no table entry for call.</span>
</div><div id="l1388" class="code_block"><span class="c">%\item[{\tt complete}] iff the table entry for {\tt Call} contains</span>
</div><div id="l1389" class="code_block"><span class="c">%all solutions.</span>
</div><div id="l1390" class="code_block"><span class="c">%\item[{\tt incomplete}] iff the table entry for {\tt Call} may not contain</span>
</div><div id="l1391" class="code_block"><span class="c">%all solutions.</span>
</div><div id="l1392" class="code_block"><span class="c">%\item[{\tt undef}] iff the predicate corresponding to {\tt Call} </span>
</div><div id="l1393" class="code_block"><span class="c">%has not been declared tabled.</span>
</div><div id="l1394" class="code_block"><span class="c">%\end{description}</span>
</div><div id="l1395" class="code_block">
</div><div id="l1396" class="code_block">| Exceptions:
</div><div id="l1397" class="code_block">|     <span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l1398" class="code_block">|     <span class="k">\item</span><span class="na">[{\tt type\_error}]</span>
</div><div id="l1399" class="code_block">|         Argument 1 is not callable.
</div><div id="l1400" class="code_block">|     <span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l1401" class="code_block"><span class="nb">}</span>
</div><div id="l1402" class="code_block">
</div><div id="l1403" class="code_block"><span class="c">%--------------------------------------------------------------------------</span>
</div><div id="l1404" class="code_block">
</div><div id="l1405" class="code_block"><span class="k">\subsection</span><span class="nb">{</span>Deleting Tables and Table Components<span class="nb">}</span>
</div><div id="l1406" class="code_block"><span class="k">\label</span><span class="nb">{</span>sec:TablePred:Deleting<span class="nb">}</span>
</div><div id="l1407" class="code_block"><span class="k">\index</span><span class="nb">{</span>tabling!table deletion<span class="nb">}</span>
</div><div id="l1408" class="code_block">
</div><div id="l1409" class="code_block">The following predicates are used to semantically invalidate tables
</div><div id="l1410" class="code_block">and/or reclaim their space. The use of the word ``tables&#39;&#39; in this
</div><div id="l1411" class="code_block">section is rather unspecific.  For the purpose of deletion a table can
</div><div id="l1412" class="code_block">either refer to a single subgoal and its answers, or to all subgoals
</div><div id="l1413" class="code_block">and answers for a tabled predicate.  Predicates are provided to
</div><div id="l1414" class="code_block">invalidate tables not only for particular predicates and subgoals, but
</div><div id="l1415" class="code_block">for all tabled predicates, all tabled predicates in a module, and in
</div><div id="l1416" class="code_block">the multi-threaded engine all thread-private tabled predicates or all
</div><div id="l1417" class="code_block">thread-shared tabled predicates.  Overall, these predicates share
</div><div id="l1418" class="code_block">similar characteristics.
</div><div id="l1419" class="code_block">
</div><div id="l1420" class="code_block">First, an incomplete tabled subgoal <span class="s">$</span><span class="nb">S</span><span class="s">$</span> may not be abolished by the
</div><div id="l1421" class="code_block">user except under special circumstances described below.  This
</div><div id="l1422" class="code_block">restriction is made since if <span class="s">$</span><span class="nb">S</span><span class="s">$</span> is incomplete there may be pointers
</div><div id="l1423" class="code_block">to <span class="s">$</span><span class="nb">S</span><span class="s">$</span> from various elements of the current execution environment, and
</div><div id="l1424" class="code_block">removing all of these pointers may be difficult to do.  If one of the
</div><div id="l1425" class="code_block">deletion predicates is called when the current execution environment
</div><div id="l1426" class="code_block">contains a reference to a <span class="nb">{</span><span class="k">\em</span> completed<span class="nb">}</span> table that is being
</div><div id="l1427" class="code_block">abolished, space for the abolished information is not immediately
</div><div id="l1428" class="code_block">reclaimed.  More precisely, if the current global tabling envonment
</div><div id="l1429" class="code_block">(including suspended states) has either
</div><div id="l1430" class="code_block"><span class="k">\begin</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l1431" class="code_block"><span class="k">\item</span> a choice point that points to an answer <span class="s">$</span><span class="nb">A</span><span class="s">$</span>; 
</div><div id="l1432" class="code_block"><span class="k">\item</span> or a (heap) delay list that points to a subgoal <span class="s">$</span><span class="nb">S</span><span class="s">$</span>
</div><div id="l1433" class="code_block"><span class="k">\end</span><span class="nb">{</span>itemize<span class="nb">}</span>
</div><div id="l1434" class="code_block">we say that <span class="s">$</span><span class="nb">A</span><span class="s">$</span> or <span class="s">$</span><span class="nb">S</span><span class="s">$</span> is <span class="nb">{</span><span class="k">\em</span> active<span class="nb">}</span>.  Also, since tables can be
</div><div id="l1435" class="code_block">abolished and rederived during the course of an evaluation, the table
</div><div id="l1436" class="code_block">deletion system marks the tables with versions.  Accordingly, if a
</div><div id="l1437" class="code_block">tabled predicate <span class="s">$</span><span class="nb">P_{version}</span><span class="s">$</span> or subgoal <span class="s">$</span><span class="nb">S_{version}</span><span class="s">$</span> to be
</div><div id="l1438" class="code_block">abolished has an answer that is active in the current environment,
</div><div id="l1439" class="code_block">reclamation of space for that version of <span class="s">$</span><span class="nb">P</span><span class="s">$</span> or <span class="s">$</span><span class="nb">S</span><span class="s">$</span> will be delayed
</div><div id="l1440" class="code_block">until no answers for <span class="s">$</span><span class="nb">P_{version}</span><span class="s">$</span> or <span class="s">$</span><span class="nb">S_{version}</span><span class="s">$</span> are active.  New
</div><div id="l1441" class="code_block">calls to <span class="s">$</span><span class="nb">P</span><span class="s">$</span> or <span class="s">$</span><span class="nb">S</span><span class="s">$</span>, however, will derive a new table versions, rather
</div><div id="l1442" class="code_block">than using the abolished information.
</div><div id="l1443" class="code_block">
</div><div id="l1444" class="code_block">When conditional answers are present, abolishing a specific table or
</div><div id="l1445" class="code_block">call may lead to semantic or implementational complications.  Consider
</div><div id="l1446" class="code_block">the conditional answer <span class="nb">{</span><span class="k">\tt</span> r(a,b):- undef|<span class="nb">}</span> from
</div><div id="l1447" class="code_block">Figure~<span class="k">\ref</span><span class="nb">{</span>ex:deletion<span class="nb">}</span>.  If the predicate <span class="nb">{</span><span class="k">\tt</span> r/2<span class="nb">}</span> (or subgoal <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1448" class="code_block">  r(a,X)<span class="nb">}</span>) is abolished and later rederived, the rederivation of <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1449" class="code_block">  r(a,X)<span class="nb">}</span> might have different semantics than the original derivation
</div><div id="l1450" class="code_block">(e.g. if <span class="nb">{</span><span class="k">\tt</span> undef<span class="nb">}</span> depended on a dynamic predicate whose definition
</div><div id="l1451" class="code_block">has changed).  From an implementation perspective, if space for <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1452" class="code_block">  r(a,X))<span class="nb">}</span> is reclaimed, then the call <span class="nb">{</span><span class="k">\tt</span> get<span class="k">\_residual</span>(p(a,X),Y)<span class="nb">}</span>
</div><div id="l1453" class="code_block">may core dump, even if there are no choice points for completed tables
</div><div id="l1454" class="code_block">anywhere in the choice point stack.  To address this problem, by
</div><div id="l1455" class="code_block">default abolishing a subgoal <span class="s">$</span><span class="nb">S</span><span class="s">$</span> (predicate <span class="s">$</span><span class="nb">P</span><span class="s">$</span>) will abolish all
</div><div id="l1456" class="code_block">`vsubgoals (predicates) that (transtively) depend on <span class="s">$</span><span class="nb">S</span><span class="s">$</span>
</div><div id="l1457" class="code_block">(<span class="s">$</span><span class="nb">P</span><span class="s">$</span>)~<span class="k">\footnote</span><span class="nb">{</span>Dao Tran Minh contributed to implementing this
</div><div id="l1458" class="code_block">  functionality.<span class="nb">}</span>.  In this case the goal <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1459" class="code_block">  abolish<span class="k">\_table\_call</span>(r(a,X))<span class="nb">}</span> would cause the deletion of <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1460" class="code_block">  p(a,X)<span class="nb">}</span> while the goal <span class="nb">{</span><span class="k">\tt</span> abolish<span class="k">\_table\_pred</span>(r/2)<span class="nb">}</span> would cause
</div><div id="l1461" class="code_block">the deletion of <span class="nb">{</span><span class="k">\tt</span> p/2<span class="nb">}</span>, since there are tabled subgoals of <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1462" class="code_block">  p/2<span class="nb">}</span> that depend on <span class="nb">{</span><span class="k">\tt</span> r/2<span class="nb">}</span>.  Only dependencies from subgoals or
</div><div id="l1463" class="code_block">answers to the answers that are conditional on them are taken into
</div><div id="l1464" class="code_block">account for table deletion: thus the deletion <span class="nb">{</span><span class="k">\tt</span> r(a,X)<span class="nb">}</span> deletes
</div><div id="l1465" class="code_block"><span class="nb">{</span><span class="k">\tt</span> p(a,X)<span class="nb">}</span>, but not <span class="nb">{</span><span class="k">\tt</span> undef<span class="nb">}</span>.
</div><div id="l1466" class="code_block">
</div><div id="l1467" class="code_block"><span class="k">\index</span><span class="nb">{</span>Prolog flags!<span class="nb">{</span><span class="k">\tt</span> table<span class="k">\_gc\_action</span><span class="nb">}}</span>
</div><div id="l1468" class="code_block">Users with programs that give rise to conditional answers in completed
</div><div id="l1469" class="code_block">tables are encouraged to maintain this default behavior.  However the
</div><div id="l1470" class="code_block">default behavior may be changed either by setting a Prolog flag:
</div><div id="l1471" class="code_block"><span class="c">%</span>
</div><div id="l1472" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1473" class="code_block">?- set<span class="nb">_</span>prolog<span class="nb">_</span>flag(table<span class="nb">_</span>gc<span class="nb">_</span>action,abolish<span class="nb">_</span>tables<span class="nb">_</span>singly).
</div><div id="l1474" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1475" class="code_block"><span class="c">%</span>
</div><div id="l1476" class="code_block">or by calling a 2-ary abolish command with <span class="nb">{</span><span class="k">\tt</span> abolish<span class="k">\_tables\_singly</span><span class="nb">}</span>
</div><div id="l1477" class="code_block">in the options list.
</div><div id="l1478" class="code_block">
</div><div id="l1479" class="code_block"><span class="k">\begin</span><span class="nb">{</span>figure<span class="nb">}</span>[htb]
</div><div id="l1480" class="code_block"><span class="k">\begin</span><span class="nb">{</span>center<span class="nb">}</span>
</div><div id="l1481" class="code_block"><span class="k">\begin</span><span class="nb">{</span>tabular<span class="nb">}{</span>cc<span class="nb">}</span><span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l1482" class="code_block"><span class="c">%\multicolumn{2}{c}{\rule{0ex}{2.5ex}\textbf{Table Deletion Example}} \\ \hline \hline</span>
</div><div id="l1483" class="code_block"><span class="k">\rule</span><span class="na">[-2ex]</span><span class="nb">{</span>0ex<span class="nb">}{</span>5ex<span class="nb">}</span> <span class="k">\textbf</span><span class="nb">{</span>Program<span class="nb">}</span> <span class="nb">&amp;</span> <span class="k">\textbf</span><span class="nb">{</span>Table<span class="nb">}</span> <span class="k">\\</span>
</div><div id="l1484" class="code_block"><span class="k">\begin</span><span class="nb">{</span>minipage<span class="nb">}{</span>14.5em<span class="nb">}</span>
</div><div id="l1485" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1486" class="code_block">:- table p/2, r/2.
</div><div id="l1487" class="code_block">p(X,Y):- r(X,Y).
</div><div id="l1488" class="code_block">
</div><div id="l1489" class="code_block">r(a,b):- undef.
</div><div id="l1490" class="code_block">r(a,c):- undef.
</div><div id="l1491" class="code_block">r(a,d):- undef.
</div><div id="l1492" class="code_block">r(a,e):- undef.
</div><div id="l1493" class="code_block">
</div><div id="l1494" class="code_block">:- table  s/0, t/0.
</div><div id="l1495" class="code_block">s:- tnot(t).
</div><div id="l1496" class="code_block">
</div><div id="l1497" class="code_block">t:- tnot(undef).
</div><div id="l1498" class="code_block">
</div><div id="l1499" class="code_block">:- table undef/0.
</div><div id="l1500" class="code_block">undef :- tnot(undef).
</div><div id="l1501" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1502" class="code_block"><span class="k">\end</span><span class="nb">{</span>minipage<span class="nb">}</span>
</div><div id="l1503" class="code_block"><span class="nb">&amp;</span>
</div><div id="l1504" class="code_block"><span class="k">\begin</span><span class="nb">{</span>tabular<span class="nb">}{</span>|c|c|c|<span class="nb">}</span> <span class="k">\hline</span>
</div><div id="l1505" class="code_block">  Subgoal <span class="nb">&amp;</span> Answer Set <span class="nb">&amp;</span> Status<span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l1506" class="code_block">  p(a,X)  <span class="nb">&amp;</span> p(a,b):- r(a,b)<span class="s">$</span><span class="nb">|</span><span class="s">$</span> <span class="nb">&amp;</span> complete <span class="k">\\</span> 
</div><div id="l1507" class="code_block">          <span class="nb">&amp;</span> p(a,c):- r(a,c)<span class="s">$</span><span class="nb">|</span><span class="s">$</span> <span class="nb">&amp;</span> <span class="k">\\</span> <span class="k">\hline</span>
</div><div id="l1508" class="code_block">  p(b,X)  <span class="nb">&amp;</span> p(b,d):- r(b,d)<span class="s">$</span><span class="nb">|</span><span class="s">$</span> <span class="nb">&amp;</span> complete <span class="k">\\</span> 
</div><div id="l1509" class="code_block">          <span class="nb">&amp;</span> p(b,d):- r(b,e)<span class="s">$</span><span class="nb">|</span><span class="s">$</span> <span class="nb">&amp;</span> <span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l1510" class="code_block">  r(a,X)  <span class="nb">&amp;</span> r(a,b):- undef<span class="s">$</span><span class="nb">|</span><span class="s">$</span>  <span class="nb">&amp;</span> complete <span class="k">\\</span> 
</div><div id="l1511" class="code_block">          <span class="nb">&amp;</span> r(a,c):- undef<span class="s">$</span><span class="nb">|</span><span class="s">$</span>  <span class="nb">&amp;</span> <span class="k">\\</span> <span class="k">\hline</span>
</div><div id="l1512" class="code_block">  r(b,X)  <span class="nb">&amp;</span> r(b,d):- undef<span class="s">$</span><span class="nb">|</span><span class="s">$</span>  <span class="nb">&amp;</span> complete <span class="k">\\</span> 
</div><div id="l1513" class="code_block">          <span class="nb">&amp;</span> r(b,d):- undef<span class="s">$</span><span class="nb">|</span><span class="s">$</span>  <span class="nb">&amp;</span> <span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l1514" class="code_block">  s       <span class="nb">&amp;</span> s:- tnot(t)<span class="s">$</span><span class="nb">|</span><span class="s">$</span>     <span class="nb">&amp;</span> complete <span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l1515" class="code_block">  t       <span class="nb">&amp;</span> t:- tnot(undef)<span class="s">$</span><span class="nb">|</span><span class="s">$</span> <span class="nb">&amp;</span> complete <span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l1516" class="code_block">  undef   <span class="nb">&amp;</span> undef:- tnot(undef)<span class="s">$</span><span class="nb">|</span><span class="s">$</span> <span class="nb">&amp;</span> complete <span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l1517" class="code_block"><span class="k">\end</span><span class="nb">{</span>tabular<span class="nb">}</span> <span class="k">\\</span>
</div><div id="l1518" class="code_block"><span class="k">\vspace*</span><span class="nb">{</span>-2ex<span class="nb">}</span> <span class="k">\\</span> <span class="k">\hline</span> <span class="k">\hline</span>
</div><div id="l1519" class="code_block"><span class="k">\end</span><span class="nb">{</span>tabular<span class="nb">}</span>
</div><div id="l1520" class="code_block"><span class="k">\end</span><span class="nb">{</span>center<span class="nb">}</span>
</div><div id="l1521" class="code_block"><span class="k">\caption</span><span class="nb">{</span>Example for Deleting Tables (Call-Variance)<span class="nb">}</span> <span class="k">\label</span><span class="nb">{</span>ex:deletion<span class="nb">}</span>
</div><div id="l1522" class="code_block"><span class="k">\end</span><span class="nb">{</span>figure<span class="nb">}</span>
</div><div id="l1523" class="code_block">
</div><div id="l1524" class="code_block">
</div><div id="l1525" class="code_block">In the multi-threaded engine abolishing tables private to a thread
</div><div id="l1526" class="code_block">behaves exactly as in the sequential engine, regardless of whether the
</div><div id="l1527" class="code_block">tables are complete or incomplete, or contain conditional answers.  In
</div><div id="l1528" class="code_block">addition, when a thread <span class="s">$</span><span class="nb">T</span><span class="s">$</span> exits (by normal termination or via an
</div><div id="l1529" class="code_block">exception), tables private to <span class="s">$</span><span class="nb">T</span><span class="s">$</span> are abolished automatically and
</div><div id="l1530" class="code_block">their space reclaimed, as are any incomplete shared tables owned by
</div><div id="l1531" class="code_block"><span class="s">$</span><span class="nb">T</span><span class="s">$</span> in local evaluation.  Shared tables can be abolished by the user
</div><div id="l1532" class="code_block">at any time, but their space will not be reclaimed until there is a
</div><div id="l1533" class="code_block">single active thread.
</div><div id="l1534" class="code_block">
</div><div id="l1535" class="code_block">As mentioned above, during normal execution, an incomplete tabled
</div><div id="l1536" class="code_block">subgoal may not be abolished by the user, a restriction that is made
</div><div id="l1537" class="code_block">to ensure correct evaluations.  Accordingly, calling an <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1538" class="code_block">  abolish<span class="k">\_xxx</span><span class="nb">}</span> predicate when tables are incomplete raises an error.
</div><div id="l1539" class="code_block">However, we note that any incomplete tables are abolished
</div><div id="l1540" class="code_block"><span class="k">\emph</span><span class="nb">{</span>automatically<span class="nb">}</span> by the system on exceptions (by the default
</div><div id="l1541" class="code_block">system error handler) when the interpreter level is resumed.
</div><div id="l1542" class="code_block">
</div><div id="l1543" class="code_block"><span class="c">% - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
</div><div id="l1544" class="code_block"><span class="k">\subsubsection</span><span class="nb">{</span>Table Deletion Predicates<span class="nb">}</span>
</div><div id="l1545" class="code_block">
</div><div id="l1546" class="code_block"><span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l1547" class="code_block"><span class="k">\index</span><span class="nb">{</span>tabling!incremental<span class="nb">}</span>
</div><div id="l1548" class="code_block"><span class="k">\ourstandarditem</span><span class="nb">{</span>abolish<span class="k">\_table\_pred</span>(+Pred)<span class="nb">}{</span>abolish<span class="k">\_table\_pred</span>/1<span class="nb">}{</span>Tabling<span class="nb">}</span>
</div><div id="l1549" class="code_block"><span class="c">%</span>
</div><div id="l1550" class="code_block">Invalidates all tabled subgoals for the predicate denoted by the
</div><div id="l1551" class="code_block">predicate or term indicator <span class="k">\code</span><span class="nb">{</span>Pred<span class="nb">}</span>.  If any subgoal for <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1552" class="code_block">  Pred<span class="nb">}</span> contains an answer <span class="s">$</span><span class="nb">A</span><span class="s">$</span> that is active in the current
</div><div id="l1553" class="code_block">enviornment, <span class="nb">{</span><span class="k">\tt</span> Pred<span class="nb">}</span> space reclamation for the <span class="nb">{</span><span class="k">\tt</span> Pred<span class="nb">}</span> tables
</div><div id="l1554" class="code_block">will be delayed until <span class="s">$</span><span class="nb">A</span><span class="s">$</span> is no longer active; otherwise the space for
</div><div id="l1555" class="code_block">the <span class="nb">{</span><span class="k">\tt</span> Pred<span class="nb">}</span> tables will be reclaimed immediately.  
</div><div id="l1556" class="code_block">
</div><div id="l1557" class="code_block"><span class="k">\index</span><span class="nb">{</span>Prolog flags!<span class="nb">{</span><span class="k">\tt</span> table<span class="k">\_gc\_action</span><span class="nb">}}</span>
</div><div id="l1558" class="code_block">If <span class="nb">{</span><span class="k">\tt</span> Pred<span class="nb">}</span> has a subgoal that contains a conditional answer, the
</div><div id="l1559" class="code_block">default behavior will be to transitively abolish any tabled predicates
</div><div id="l1560" class="code_block">with subgoals having answers that depend on any conditional answers of
</div><div id="l1561" class="code_block"><span class="s">$</span><span class="nb">S</span><span class="s">$</span>.  This default may be changed either by setting a Prolog flag:
</div><div id="l1562" class="code_block"><span class="c">%</span>
</div><div id="l1563" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1564" class="code_block">?- set<span class="nb">_</span>xsb<span class="nb">_</span>flag(table<span class="nb">_</span>gc<span class="nb">_</span>action,abolish<span class="nb">_</span>tables<span class="nb">_</span>singly).
</div><div id="l1565" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1566" class="code_block"><span class="c">% </span>
</div><div id="l1567" class="code_block">or by calling <span class="nb">{</span><span class="k">\tt</span> abolish<span class="k">\_table\_pred</span>/2<span class="nb">}</span> with the appropriate
</div><div id="l1568" class="code_block">option.  If the transitive abolishes are turned off, and <span class="nb">{</span><span class="k">\tt</span> Pred<span class="nb">}</span>
</div><div id="l1569" class="code_block">contains a conditional answer, the warning
</div><div id="l1570" class="code_block">
</div><div id="l1571" class="code_block"><span class="nb">{</span><span class="k">\tt</span> abolish<span class="k">\_table\_pred</span>/[1,2] is deleting a table with
</div><div id="l1572" class="code_block">  conditional<span class="k">\</span> answers: <span class="k">\\</span> delay dependencies may be corrupted.<span class="nb">}</span>
</div><div id="l1573" class="code_block">
</div><div id="l1574" class="code_block">will be issued.  
</div><div id="l1575" class="code_block">
</div><div id="l1576" class="code_block">In the multi-threaded engine, if <span class="nb">{</span><span class="k">\tt</span> Pred<span class="nb">}</span> is shared, reclamation for
</div><div id="l1577" class="code_block"><span class="nb">{</span><span class="k">\tt</span> Pred<span class="nb">}</span> will be delayed until there is a single active thread and
</div><div id="l1578" class="code_block">no answer in <span class="nb">{</span><span class="k">\tt</span> Pred<span class="nb">}</span> is active in the current execution
</div><div id="l1579" class="code_block">environment.  Otherwise, the behavior of <span class="nb">{</span><span class="k">\tt</span> abolish<span class="k">\_table\_pred</span>/1<span class="nb">}</span>
</div><div id="l1580" class="code_block">is the same as in the sequential engine.
</div><div id="l1581" class="code_block">
</div><div id="l1582" class="code_block">Finally, <span class="nb">{</span><span class="k">\tt</span> abolish<span class="k">\_table\_pred</span>/1<span class="nb">}</span> will throw an error if the
</div><div id="l1583" class="code_block">predicate to be abolished is incremental.  This is because abolishing
</div><div id="l1584" class="code_block">some incremental tables but not others will leave dangling pointers in
</div><div id="l1585" class="code_block">the data structures used for uncremental updates.  Until <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1586" class="code_block">  abolish<span class="k">\_table\_pred</span>/[1,2]<span class="nb">}</span> is extended to support incremental
</div><div id="l1587" class="code_block">tables, use <span class="nb">{</span><span class="k">\tt</span> abolish<span class="k">\_table\_call</span>/[1,2]<span class="nb">}</span> or <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1588" class="code_block">  abolish<span class="k">\_all\_tables</span>/0<span class="nb">}</span>.
</div><div id="l1589" class="code_block">
</div><div id="l1590" class="code_block"><span class="nb">{</span><span class="k">\bf</span> Error Cases<span class="nb">}</span>
</div><div id="l1591" class="code_block"><span class="k">\bi</span>
</div><div id="l1592" class="code_block"><span class="c">%</span>
</div><div id="l1593" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> Pred<span class="nb">}</span> is not instantiated
</div><div id="l1594" class="code_block"> <span class="k">\bi</span> 
</div><div id="l1595" class="code_block"> <span class="k">\item</span> 	<span class="nb">{</span><span class="k">\tt</span> instantiation<span class="k">\_error</span><span class="nb">}</span>
</div><div id="l1596" class="code_block"> <span class="k">\ei</span>
</div><div id="l1597" class="code_block"><span class="c">%</span>
</div><div id="l1598" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> PredSpec<span class="nb">}</span> is not a predicate<span class="k">\_indicator</span> or a term<span class="k">\_indicator</span>
</div><div id="l1599" class="code_block"> <span class="k">\bi</span>
</div><div id="l1600" class="code_block"> <span class="k">\item</span> 	<span class="nb">{</span><span class="k">\tt</span> domain<span class="k">\_error</span>(predicate<span class="k">\_or\_term\_indicator</span>,Pred)<span class="nb">}</span>
</div><div id="l1601" class="code_block"> <span class="k">\ei</span>
</div><div id="l1602" class="code_block"><span class="c">%</span>
</div><div id="l1603" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> PredSpec<span class="nb">}</span> does not indicate a tabled predicate or indicates
</div><div id="l1604" class="code_block">  an incrementally tabled predicate.
</div><div id="l1605" class="code_block">  <span class="k">\bi</span>
</div><div id="l1606" class="code_block"> <span class="k">\item</span> 	<span class="nb">{</span><span class="k">\tt</span> table<span class="k">\_error</span><span class="nb">}</span>
</div><div id="l1607" class="code_block"> <span class="k">\ei</span>
</div><div id="l1608" class="code_block"><span class="c">%</span>
</div><div id="l1609" class="code_block"><span class="k">\item</span> There is currently an incomplete table for an atomic subgoal of
</div><div id="l1610" class="code_block">  <span class="nb">{</span><span class="k">\tt</span> Pred<span class="nb">}</span>
</div><div id="l1611" class="code_block"> <span class="k">\bi</span>
</div><div id="l1612" class="code_block"> <span class="k">\item</span> 	<span class="nb">{</span><span class="k">\tt</span> table<span class="k">\_error</span><span class="nb">}</span>
</div><div id="l1613" class="code_block"> <span class="k">\ei</span>
</div><div id="l1614" class="code_block"><span class="c">%</span>
</div><div id="l1615" class="code_block"><span class="k">\ei</span>
</div><div id="l1616" class="code_block">
</div><div id="l1617" class="code_block"><span class="k">\index</span><span class="nb">{</span>Prolog flags!<span class="nb">{</span><span class="k">\tt</span> table<span class="k">\_gc\_action</span><span class="nb">}}</span>
</div><div id="l1618" class="code_block"><span class="k">\ourstandarditem</span><span class="nb">{</span>abolish<span class="k">\_table\_pred</span>(+CallTerm,+Options)<span class="nb">}{</span>abolish<span class="k">\_table\_pred</span>/2<span class="nb">}{</span>Tabling<span class="nb">}</span>
</div><div id="l1619" class="code_block"><span class="c">%</span>
</div><div id="l1620" class="code_block">Behaves as <span class="nb">{</span>abolish<span class="k">\_table\_pred</span>/1<span class="nb">}</span>, but allows the default <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1621" class="code_block">  table<span class="k">\_gc\_action</span><span class="nb">}</span> to be over-ridden with a flag, which can be either 
</div><div id="l1622" class="code_block"><span class="nb">{</span><span class="k">\tt</span> abolish<span class="k">\_tables\_transitively</span><span class="nb">}</span> or <span class="nb">{</span><span class="k">\tt</span> abolish<span class="k">\_tables\_singly</span><span class="nb">}</span>.
</div><div id="l1623" class="code_block">
</div><div id="l1624" class="code_block"><span class="nb">{</span><span class="k">\bf</span> Error Cases<span class="nb">}</span> Error cases are the same as <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1625" class="code_block">  abolish<span class="k">\_table\_pred</span>/1<span class="nb">}</span> but with the additions: 
</div><div id="l1626" class="code_block"><span class="k">\bi</span>
</div><div id="l1627" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> Options<span class="nb">}</span> is a variable, or contains a variable as an element
</div><div id="l1628" class="code_block"><span class="k">\bi</span>
</div><div id="l1629" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> instantiation<span class="k">\_error</span><span class="nb">}</span>
</div><div id="l1630" class="code_block"><span class="k">\ei</span>
</div><div id="l1631" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> Options<span class="nb">}</span> is not a list
</div><div id="l1632" class="code_block"><span class="k">\bi</span>
</div><div id="l1633" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> type<span class="k">\_error</span>(list,Options)<span class="nb">}</span>
</div><div id="l1634" class="code_block"><span class="k">\ei</span>
</div><div id="l1635" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> Options<span class="nb">}</span> contains an option <span class="nb">{</span><span class="k">\tt</span> O<span class="nb">}</span> that is not a
</div><div id="l1636" class="code_block">  table abolish option.
</div><div id="l1637" class="code_block"><span class="k">\bi</span>
</div><div id="l1638" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> domain<span class="k">\_error</span>([abolish<span class="k">\_tables\_transitively</span>, abolish<span class="k">\_tables\_singly</span>,O)<span class="nb">}</span>
</div><div id="l1639" class="code_block"><span class="k">\ei</span>
</div><div id="l1640" class="code_block"><span class="k">\ei</span>
</div><div id="l1641" class="code_block"><span class="c">% - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
</div><div id="l1642" class="code_block">
</div><div id="l1643" class="code_block"><span class="k">\ourstandarditem</span><span class="nb">{</span>abolish<span class="k">\_table\_call</span>(+CallTerm)<span class="nb">}{</span>abolish<span class="k">\_table\_call</span>/1<span class="nb">}{</span>Tabling<span class="nb">}</span>
</div><div id="l1644" class="code_block"><span class="c">%</span>
</div><div id="l1645" class="code_block">Invalidates all entries from the table for any subgoals that unify
</div><div id="l1646" class="code_block">with <span class="nb">{</span><span class="k">\tt</span> CallTerm<span class="nb">}</span>.  If a subgoal <span class="s">$</span><span class="nb">S</span><span class="s">$</span> unifying with <span class="nb">{</span><span class="k">\tt</span> CallTerm<span class="nb">}</span>
</div><div id="l1647" class="code_block">contains an answer <span class="s">$</span><span class="nb">A</span><span class="s">$</span> that is active in the current enviornment, the
</div><div id="l1648" class="code_block">table entry for <span class="s">$</span><span class="nb">S</span><span class="s">$</span> will not be reclaimed until <span class="s">$</span><span class="nb">A</span><span class="s">$</span> is no longer
</div><div id="l1649" class="code_block">active; otherwise the space for <span class="s">$</span><span class="nb">S</span><span class="s">$</span> will be reclaimed immediately.
</div><div id="l1650" class="code_block">
</div><div id="l1651" class="code_block"><span class="k">\index</span><span class="nb">{</span>Prolog flags!<span class="nb">{</span><span class="k">\tt</span> table<span class="k">\_gc\_action</span><span class="nb">}}</span>
</div><div id="l1652" class="code_block">If <span class="s">$</span><span class="nb">S</span><span class="s">$</span> contains a conditional answer, the default behavior will be to
</div><div id="l1653" class="code_block">transitively abolish any subgoals that depend on any conditional
</div><div id="l1654" class="code_block">answers of <span class="s">$</span><span class="nb">S</span><span class="s">$</span>.  This default may be changed either by setting an XSB
</div><div id="l1655" class="code_block">flag:
</div><div id="l1656" class="code_block"><span class="c">%</span>
</div><div id="l1657" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1658" class="code_block">?- set<span class="nb">_</span>xsb<span class="nb">_</span>flag(table<span class="nb">_</span>gc<span class="nb">_</span>action,abolish<span class="nb">_</span>tables<span class="nb">_</span>singly).
</div><div id="l1659" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1660" class="code_block"><span class="c">% </span>
</div><div id="l1661" class="code_block">or by calling <span class="nb">{</span><span class="k">\tt</span> abolish<span class="k">\_table\_call</span>/2<span class="nb">}</span> with the appropriate
</div><div id="l1662" class="code_block">option.  If the transitive abolishes are turned off, and <span class="s">$</span><span class="nb">S</span><span class="s">$</span> contains
</div><div id="l1663" class="code_block">a conditional answer, the warning
</div><div id="l1664" class="code_block">
</div><div id="l1665" class="code_block"><span class="nb">{</span><span class="k">\tt</span> abolish<span class="k">\_table\_call</span>/1 is deleting a table with
</div><div id="l1666" class="code_block">  conditional<span class="k">\</span> answers: <span class="k">\\</span> delay dependencies may be corrupted.<span class="nb">}</span>
</div><div id="l1667" class="code_block">
</div><div id="l1668" class="code_block">will be issued.  
</div><div id="l1669" class="code_block">
</div><div id="l1670" class="code_block">In the multi-threaded engine, if <span class="s">$</span><span class="nb">S</span><span class="s">$</span> is a subgoal for a predicate that
</div><div id="l1671" class="code_block">is shared, reclamation for <span class="s">$</span><span class="nb">S</span><span class="s">$</span> will be delayed until there is a single
</div><div id="l1672" class="code_block">active thread and no answer in <span class="s">$</span><span class="nb">S</span><span class="s">$</span> is active in the current execution
</div><div id="l1673" class="code_block">environment.  Otherwise, the behavior of <span class="nb">{</span><span class="k">\tt</span> abolish<span class="k">\_table\_call</span>/1<span class="nb">}</span>
</div><div id="l1674" class="code_block">is the same as in the sequential engine on tabled predicates that are
</div><div id="l1675" class="code_block">thread-private.
</div><div id="l1676" class="code_block">
</div><div id="l1677" class="code_block"><span class="nb">{</span><span class="k">\tt</span> abolish<span class="k">\_table\_call</span>/[1,2]<span class="nb">}</span> also cascades abolishes for
</div><div id="l1678" class="code_block">incremental tables.  If a call <span class="s">$</span><span class="nb">G</span><span class="s">$</span> is abolished, all calls that <span class="s">$</span><span class="nb">G</span><span class="s">$</span>
</div><div id="l1679" class="code_block">depends on will also be abolished, so that the dependency structures
</div><div id="l1680" class="code_block">that support incremental tabling will remain in a consistent state.
</div><div id="l1681" class="code_block">
</div><div id="l1682" class="code_block"><span class="nb">{</span><span class="k">\bf</span> Error Cases<span class="nb">}</span>
</div><div id="l1683" class="code_block"><span class="k">\bi</span>
</div><div id="l1684" class="code_block"><span class="k">\item</span> The term spec <span class="nb">{</span><span class="k">\tt</span> CallTerm<span class="nb">}</span> does not correspond to a tabled predicate:
</div><div id="l1685" class="code_block"><span class="k">\bi</span>
</div><div id="l1686" class="code_block"><span class="k">\item</span> 	<span class="nb">{</span><span class="k">\tt</span> table<span class="k">\_error</span><span class="nb">}</span>
</div><div id="l1687" class="code_block"><span class="k">\ei</span>
</div><div id="l1688" class="code_block"><span class="k">\item</span> The term spec <span class="nb">{</span><span class="k">\tt</span> CallTerm<span class="nb">}</span> unifies with a tabled subgoal that is incomplete:
</div><div id="l1689" class="code_block"><span class="k">\bi</span>
</div><div id="l1690" class="code_block"><span class="k">\item</span> 	<span class="nb">{</span><span class="k">\tt</span> table<span class="k">\_error</span><span class="nb">}</span>
</div><div id="l1691" class="code_block"><span class="k">\ei</span>
</div><div id="l1692" class="code_block"><span class="k">\item</span> The term spec <span class="nb">{</span><span class="k">\tt</span> CallTerm<span class="nb">}</span> is a cyclic term::
</div><div id="l1693" class="code_block"><span class="k">\bi</span>
</div><div id="l1694" class="code_block"><span class="k">\item</span> 	<span class="nb">{</span><span class="k">\tt</span> table<span class="k">\_error</span><span class="nb">}</span>
</div><div id="l1695" class="code_block"><span class="k">\ei</span>
</div><div id="l1696" class="code_block"><span class="c">%\item {\tt CallTerm} unifies with a table that is formed from a</span>
</div><div id="l1697" class="code_block"><span class="c">%  predicate that does not use variant tabling.  </span>
</div><div id="l1698" class="code_block"><span class="c">%\bi</span>
</div><div id="l1699" class="code_block"><span class="c">%\item 	{\tt table\_error}</span>
</div><div id="l1700" class="code_block"><span class="c">%t\ei</span>
</div><div id="l1701" class="code_block"><span class="k">\ei</span>
</div><div id="l1702" class="code_block"><span class="c">%</span>
</div><div id="l1703" class="code_block">
</div><div id="l1704" class="code_block"><span class="k">\index</span><span class="nb">{</span>Prolog flags!<span class="nb">{</span><span class="k">\tt</span> table<span class="k">\_gc\_action</span><span class="nb">}}</span>
</div><div id="l1705" class="code_block"><span class="k">\ourstandarditem</span><span class="nb">{</span>abolish<span class="k">\_table\_call</span>(+CallTerm,+Options)<span class="nb">}{</span>abolish<span class="k">\_table\_call</span>/2<span class="nb">}{</span>Tabling<span class="nb">}</span>
</div><div id="l1706" class="code_block"><span class="c">%</span>
</div><div id="l1707" class="code_block">Behaves as <span class="nb">{</span>abolish<span class="k">\_table\_call</span>/1<span class="nb">}</span>, but allows the default <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1708" class="code_block">  table<span class="k">\_gc\_action</span><span class="nb">}</span> to be over-ridden with a flag, which can be either 
</div><div id="l1709" class="code_block"><span class="nb">{</span><span class="k">\tt</span> abolish<span class="k">\_tables\_transitively</span><span class="nb">}</span> or <span class="nb">{</span><span class="k">\tt</span> abolish<span class="k">\_tables\_singly</span><span class="nb">}</span>.
</div><div id="l1710" class="code_block">
</div><div id="l1711" class="code_block"><span class="nb">{</span><span class="k">\bf</span> Error Cases<span class="nb">}</span> Error cases are the same as <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1712" class="code_block">  abolish<span class="k">\_table\_call</span>/1<span class="nb">}</span> but with the additions: 
</div><div id="l1713" class="code_block"><span class="k">\bi</span>
</div><div id="l1714" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> Options<span class="nb">}</span> is a variable, or contains a variable as an element
</div><div id="l1715" class="code_block"><span class="k">\bi</span>
</div><div id="l1716" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> instantiation<span class="k">\_error</span><span class="nb">}</span>
</div><div id="l1717" class="code_block"><span class="k">\ei</span>
</div><div id="l1718" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> Options<span class="nb">}</span> is not a list
</div><div id="l1719" class="code_block"><span class="k">\bi</span>
</div><div id="l1720" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> type<span class="k">\_error</span>(list,Options)<span class="nb">}</span>
</div><div id="l1721" class="code_block"><span class="k">\ei</span>
</div><div id="l1722" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> Options<span class="nb">}</span> contains an option <span class="nb">{</span><span class="k">\tt</span> O<span class="nb">}</span> that is not a
</div><div id="l1723" class="code_block">  table abolish option.
</div><div id="l1724" class="code_block"><span class="k">\bi</span>
</div><div id="l1725" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> domain<span class="k">\_error</span>([abolish<span class="k">\_tables\_transitively</span>, abolish<span class="k">\_tables\_singly</span>,O)<span class="nb">}</span>
</div><div id="l1726" class="code_block"><span class="k">\ei</span>
</div><div id="l1727" class="code_block"><span class="k">\ei</span>
</div><div id="l1728" class="code_block">
</div><div id="l1729" class="code_block">
</div><div id="l1730" class="code_block">
</div><div id="l1731" class="code_block"><span class="c">% - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
</div><div id="l1732" class="code_block">
</div><div id="l1733" class="code_block"><span class="k">\ourstandarditem</span><span class="nb">{</span>abolish<span class="k">\_all\_tables</span><span class="nb">}{</span>abolish<span class="k">\_all\_tables</span>/0<span class="nb">}{</span>Tabling<span class="nb">}</span>
</div><div id="l1734" class="code_block"><span class="c">%</span>
</div><div id="l1735" class="code_block">In the single-threaded engine, removes all tables presently in the
</div><div id="l1736" class="code_block">system and frees all the memory held by XSB for these structures.
</div><div id="l1737" class="code_block">Predicates that have been declared tabled remain so, but information
</div><div id="l1738" class="code_block">in their table is deleted.  <span class="nb">{</span><span class="k">\tt</span> abolish<span class="k">\_all\_tables</span>/0<span class="nb">}</span> works
</div><div id="l1739" class="code_block">directly on the memory structures allocated for table space.  This
</div><div id="l1740" class="code_block">makes it very fast for abolishing a large amount of tables, and to
</div><div id="l1741" class="code_block">maintain its speed it throws an error if any completed answer <span class="s">$</span><span class="nb">A</span><span class="s">$</span> is
</div><div id="l1742" class="code_block">active in the current execution environment.  <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1743" class="code_block">  abolish<span class="k">\_all\_tables</span>/0<span class="nb">}</span> can be used regardless of whether there are
</div><div id="l1744" class="code_block">incremental tables, or tables that use call or answer subsumption.
</div><div id="l1745" class="code_block">
</div><div id="l1746" class="code_block">In the multi-threaded engine <span class="nb">{</span><span class="k">\tt</span> abolish<span class="k">\_all\_tables</span>/0<span class="nb">}</span> raises an
</div><div id="l1747" class="code_block">error unless it is called when there is a single active thread.  In
</div><div id="l1748" class="code_block">that case, all shared tables are abolished as well as all private
</div><div id="l1749" class="code_block">tables for the main thread.  An error will be thrown if any completed
</div><div id="l1750" class="code_block">answer <span class="s">$</span><span class="nb">A</span><span class="s">$</span> is active in the current environment, regardless of whether
</div><div id="l1751" class="code_block"><span class="s">$</span><span class="nb">A</span><span class="s">$</span> is thread-private or thread-shared.  
</div><div id="l1752" class="code_block">
</div><div id="l1753" class="code_block">
</div><div id="l1754" class="code_block">
</div><div id="l1755" class="code_block"><span class="nb">{</span><span class="k">\bf</span> Error Cases<span class="nb">}</span>
</div><div id="l1756" class="code_block"><span class="k">\bi</span>
</div><div id="l1757" class="code_block"><span class="k">\item</span> There are incomplete tables at the time of the predicate&#39;s call;
</div><div id="l1758" class="code_block"><span class="k">\bi</span>
</div><div id="l1759" class="code_block"><span class="k">\item</span> 	<span class="nb">{</span><span class="k">\tt</span> table<span class="k">\_error</span><span class="nb">}</span>
</div><div id="l1760" class="code_block"><span class="k">\ei</span>
</div><div id="l1761" class="code_block"><span class="k">\item</span> The current execution environment has an active answer <span class="s">$</span><span class="nb">A</span><span class="s">$</span>
</div><div id="l1762" class="code_block"><span class="k">\bi</span>
</div><div id="l1763" class="code_block"><span class="k">\item</span> 	<span class="nb">{</span><span class="k">\tt</span> table<span class="k">\_error</span><span class="nb">}</span>
</div><div id="l1764" class="code_block"><span class="k">\ei</span>
</div><div id="l1765" class="code_block"><span class="k">\item</span> (Multi-threaded engine only) More than one thread is active:
</div><div id="l1766" class="code_block"><span class="k">\bi</span>
</div><div id="l1767" class="code_block"><span class="k">\item</span> 	<span class="nb">{</span><span class="k">\tt</span> table<span class="k">\_error</span><span class="nb">}</span>
</div><div id="l1768" class="code_block"><span class="k">\ei</span>
</div><div id="l1769" class="code_block"><span class="c">%</span>
</div><div id="l1770" class="code_block"><span class="c">%</span>
</div><div id="l1771" class="code_block"><span class="k">\ei</span>
</div><div id="l1772" class="code_block">
</div><div id="l1773" class="code_block"><span class="c">% - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
</div><div id="l1774" class="code_block">
</div><div id="l1775" class="code_block"><span class="k">\ourstandarditem</span><span class="nb">{</span>abolish<span class="k">\_all\_private\_tables</span><span class="nb">}{</span>abolish<span class="k">\_all\_private\_tables</span>/0<span class="nb">}{</span>Tabling<span class="nb">}</span>
</div><div id="l1776" class="code_block"><span class="c">%</span>
</div><div id="l1777" class="code_block">In the multi-threaded engine, removes all tables private to the thread
</div><div id="l1778" class="code_block">and frees all the memory held by XSB for these structures, including
</div><div id="l1779" class="code_block">space for conditional answers.  Predicates that have been declared
</div><div id="l1780" class="code_block">tabled remain so, but information in their table is deleted.  <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1781" class="code_block">  abolish<span class="k">\_all\_private\_tables</span>/0<span class="nb">}</span> works directly on the memory
</div><div id="l1782" class="code_block">structures allocated for table space.  This makes it very fast for
</div><div id="l1783" class="code_block">abolishing a large amount of tables, and to maintain its speed it
</div><div id="l1784" class="code_block">throws an error if any completed answer <span class="s">$</span><span class="nb">A</span><span class="s">$</span> for a private table is
</div><div id="l1785" class="code_block">active in the current execution environment.
</div><div id="l1786" class="code_block">
</div><div id="l1787" class="code_block"><span class="c">%In the single-threaded engine, {\tt abolish\_all\_private\_tables/0}</span>
</div><div id="l1788" class="code_block"><span class="c">%is defined as {\tt abolish\_all\_tables/0}.</span>
</div><div id="l1789" class="code_block">
</div><div id="l1790" class="code_block"><span class="nb">{</span><span class="k">\bf</span> Error Cases<span class="nb">}</span>
</div><div id="l1791" class="code_block"><span class="k">\bi</span>
</div><div id="l1792" class="code_block"><span class="k">\item</span> There are incomplete tables at the time of the predicate&#39;s call;
</div><div id="l1793" class="code_block"><span class="k">\bi</span>
</div><div id="l1794" class="code_block"><span class="k">\item</span> 	<span class="nb">{</span><span class="k">\tt</span> table<span class="k">\_error</span><span class="nb">}</span>
</div><div id="l1795" class="code_block"><span class="k">\ei</span>
</div><div id="l1796" class="code_block"><span class="k">\item</span> The current execution environment for the thread has an active
</div><div id="l1797" class="code_block">  answer <span class="s">$</span><span class="nb">A</span><span class="s">$</span> for a private table.  
</div><div id="l1798" class="code_block"><span class="k">\bi</span>
</div><div id="l1799" class="code_block"><span class="k">\item</span> 	<span class="nb">{</span><span class="k">\tt</span> table<span class="k">\_error</span><span class="nb">}</span>
</div><div id="l1800" class="code_block"><span class="k">\ei</span>
</div><div id="l1801" class="code_block"><span class="c">%</span>
</div><div id="l1802" class="code_block"><span class="k">\ei</span>
</div><div id="l1803" class="code_block">
</div><div id="l1804" class="code_block"><span class="c">% - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
</div><div id="l1805" class="code_block">
</div><div id="l1806" class="code_block"><span class="k">\ourstandarditem</span><span class="nb">{</span>abolish<span class="k">\_all\_shared\_tables</span><span class="nb">}{</span>abolish<span class="k">\_all\_shared\_tables</span>/0<span class="nb">}{</span>Tabling<span class="nb">}</span>
</div><div id="l1807" class="code_block"><span class="c">%</span>
</div><div id="l1808" class="code_block">In the multi-threaded engine, removes all tables private to the thread
</div><div id="l1809" class="code_block">and frees all the memory held by XSB for these structures, including
</div><div id="l1810" class="code_block">space for conditional answers.  Predicates that have been declared
</div><div id="l1811" class="code_block">tabled remain so, but information in their table is deleted.  <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1812" class="code_block">  abolish<span class="k">\_all\_private\_tables</span>/0<span class="nb">}</span> works directly on the memory
</div><div id="l1813" class="code_block">structures allocated for table space.  This makes it very fast for
</div><div id="l1814" class="code_block">abolishing a large amount of tables, and to maintain its speed it
</div><div id="l1815" class="code_block">throws an error if any completed answer <span class="s">$</span><span class="nb">A</span><span class="s">$</span> for a private table is
</div><div id="l1816" class="code_block">active in the current execution environment.  <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1817" class="code_block">  abolish<span class="k">\_all\_shared\_tables</span>/0<span class="nb">}</span> raises an error unless it is called
</div><div id="l1818" class="code_block">when there is a single active thread.  In that case, all shared tables
</div><div id="l1819" class="code_block">are abolished, but private tables for the main thread are unaffected.
</div><div id="l1820" class="code_block">
</div><div id="l1821" class="code_block"><span class="nb">{</span><span class="k">\bf</span> Error Cases<span class="nb">}</span>
</div><div id="l1822" class="code_block"><span class="k">\bi</span>
</div><div id="l1823" class="code_block"><span class="k">\item</span> There are incomplete tables at the time of the predicate&#39;s call;
</div><div id="l1824" class="code_block"><span class="k">\bi</span>
</div><div id="l1825" class="code_block"><span class="k">\item</span> 	<span class="nb">{</span><span class="k">\tt</span> table<span class="k">\_error</span><span class="nb">}</span>
</div><div id="l1826" class="code_block"><span class="k">\ei</span>
</div><div id="l1827" class="code_block"><span class="k">\item</span> The current execution environment has an active answer <span class="s">$</span><span class="nb">A</span><span class="s">$</span>
</div><div id="l1828" class="code_block"><span class="k">\bi</span>
</div><div id="l1829" class="code_block"><span class="k">\item</span> 	<span class="nb">{</span><span class="k">\tt</span> table<span class="k">\_error</span><span class="nb">}</span>
</div><div id="l1830" class="code_block"><span class="k">\ei</span>
</div><div id="l1831" class="code_block"><span class="k">\item</span> More than one thread is active:
</div><div id="l1832" class="code_block"><span class="k">\bi</span>
</div><div id="l1833" class="code_block"><span class="k">\item</span> 	<span class="nb">{</span><span class="k">\tt</span> table<span class="k">\_error</span><span class="nb">}</span>
</div><div id="l1834" class="code_block"><span class="k">\ei</span>
</div><div id="l1835" class="code_block"><span class="c">%</span>
</div><div id="l1836" class="code_block"><span class="c">%</span>
</div><div id="l1837" class="code_block"><span class="k">\ei</span>
</div><div id="l1838" class="code_block">
</div><div id="l1839" class="code_block"><span class="c">% - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
</div><div id="l1840" class="code_block"><span class="k">\comment</span><span class="nb">{</span>
</div><div id="l1841" class="code_block"><span class="c">% \ournewitem{abolish\_tables(+OptionsList)}{Tabling}</span>
</div><div id="l1842" class="code_block"><span class="c">% \index{\texttt{abolish\_tables/1}}</span>
</div><div id="l1843" class="code_block">
</div><div id="l1844" class="code_block"><span class="c">% Removes tables as specified by options in {\tt OptionsList}, which is</span>
</div><div id="l1845" class="code_block"><span class="c">% a list of terms of the form:</span>
</div><div id="l1846" class="code_block">
</div><div id="l1847" class="code_block"><span class="c">% \begin{itemize}</span>
</div><div id="l1848" class="code_block">
</div><div id="l1849" class="code_block"><span class="c">% \item {\tt private} In the multi-threaded engine, this option</span>
</div><div id="l1850" class="code_block"><span class="c">%   abolishes all tables private to the calling thread.  In the</span>
</div><div id="l1851" class="code_block"><span class="c">%   sequential engine, this option abolishes all tables.</span>
</div><div id="l1852" class="code_block">
</div><div id="l1853" class="code_block"><span class="c">% \item {\tt shared} In the multi-threaded engine, this option abolishes</span>
</div><div id="l1854" class="code_block"><span class="c">%   all thread-shared tables.  Space reclamation for thread-shared</span>
</div><div id="l1855" class="code_block"><span class="c">%   tables may not be performed until there is a single active thread.</span>
</div><div id="l1856" class="code_block"><span class="c">%   In the sequential engine, this option has no effect.</span>
</div><div id="l1857" class="code_block">
</div><div id="l1858" class="code_block"><span class="c">% \item {\tt module(+Module)} Abolishes all tables in a given module,</span>
</div><div id="l1859" class="code_block"><span class="c">%   whether they are shared or private.  If {\tt Module} is set to {\tt</span>
</div><div id="l1860" class="code_block"><span class="c">%     usermod}, all tables not explicitly placed into a module are</span>
</div><div id="l1861" class="code_block"><span class="c">%   abolished.</span>
</div><div id="l1862" class="code_block">
</div><div id="l1863" class="code_block"><span class="c">% \item {\tt pred(+PredSpecifier)} Abolishes the tabled predicate</span>
</div><div id="l1864" class="code_block"><span class="c">%   referred to by {\tt PredSpecifier}, regardless of whether it is</span>
</div><div id="l1865" class="code_block"><span class="c">%   shared or private.  </span>
</div><div id="l1866" class="code_block">
</div><div id="l1867" class="code_block"><span class="c">% \end{itemize}</span>
</div><div id="l1868" class="code_block">
</div><div id="l1869" class="code_block"><span class="c">% When {\tt OptionsList} contains several options, the options are taken</span>
</div><div id="l1870" class="code_block"><span class="c">% to be disjunctive in that any table that is covered by at least one of</span>
</div><div id="l1871" class="code_block"><span class="c">% the options will be abolished.  For instance</span>
</div><div id="l1872" class="code_block"><span class="c">% \begin{verbatim}</span>
</div><div id="l1873" class="code_block"><span class="c">%     abolish_tables([private,module(cdf),predicate(f/2)])</span>
</div><div id="l1874" class="code_block"><span class="c">% \end{verbatim}</span>
</div><div id="l1875" class="code_block"><span class="c">% abolishes all tables that are private {\em or} in the module {\tt cdf}</span>
</div><div id="l1876" class="code_block"><span class="c">% {\em or} have been created by calls to the predicate {\tt f/2}.</span>
</div><div id="l1877" class="code_block"><span class="nb">}</span>
</div><div id="l1878" class="code_block"><span class="c">% - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
</div><div id="l1879" class="code_block"><span class="k">\ourstandarditem</span><span class="nb">{</span>abolish<span class="k">\_module\_tables</span>(+Module)<span class="nb">}{</span>abolish<span class="k">\_module\_tables</span>/1<span class="nb">}{</span>Tabling<span class="nb">}</span>
</div><div id="l1880" class="code_block"><span class="c">%</span>
</div><div id="l1881" class="code_block">Given a module name (or the default module, <span class="nb">{</span><span class="k">\tt</span> usermod<span class="nb">}</span>), this
</div><div id="l1882" class="code_block">predicate abolishes all tables for each tabled predicate in <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1883" class="code_block">  Module<span class="nb">}</span>.  It is implemented using a series of calls to <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1884" class="code_block">  abolish<span class="k">\_table\_pred</span>/1<span class="nb">}</span> and so inherits the behavior of that
</div><div id="l1885" class="code_block">predicate.
</div><div id="l1886" class="code_block">
</div><div id="l1887" class="code_block"><span class="c">% - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
</div><div id="l1888" class="code_block">
</div><div id="l1889" class="code_block"><span class="k">\ourstandarditem</span><span class="nb">{</span>gc<span class="k">\_tables</span>(-Number)<span class="nb">}{</span>gc<span class="k">\_tables</span>/1<span class="nb">}{</span>Tabling<span class="nb">}</span>
</div><div id="l1890" class="code_block"><span class="k">\index</span><span class="nb">{</span>garbage collection!tables<span class="nb">}</span>
</div><div id="l1891" class="code_block"><span class="c">%</span>
</div><div id="l1892" class="code_block">When a tabled subgoal or predicate is abolished, reclamation of its
</div><div id="l1893" class="code_block">space may be postponed if the subgoal or predicate has an answer that
</div><div id="l1894" class="code_block">is active in the current environment.  A garbage collection routine is
</div><div id="l1895" class="code_block">called at various points in execution to check which answers are
</div><div id="l1896" class="code_block">active in the current environment, and to reclaim the space for
</div><div id="l1897" class="code_block">subgoals and predicates with no active answers.  In particular, space
</div><div id="l1898" class="code_block">for all abolished tables is reclaimed whenever the engine re-executes
</div><div id="l1899" class="code_block">the main command-line or C thread interpreter code.  However for
</div><div id="l1900" class="code_block">certain applications this strategy may not be adequate.  For this
</div><div id="l1901" class="code_block">reason, the user can explicitly call the table garbage collector
</div><div id="l1902" class="code_block">to reclaim space for any deleted tabled predicates or subgoals that no
</div><div id="l1903" class="code_block">longer have active answers.
</div><div id="l1904" class="code_block">
</div><div id="l1905" class="code_block"><span class="nb">{</span><span class="k">\tt</span> gc<span class="k">\_tables</span>/1<span class="nb">}</span> always succeeds, unifying <span class="nb">{</span><span class="k">\tt</span> Number<span class="nb">}</span> to <span class="s">$</span><span class="o">-</span><span class="m">1</span><span class="s">$</span> if
</div><div id="l1906" class="code_block">garbage collection was not attempted (due to multiple active threads)
</div><div id="l1907" class="code_block">and otherwise to the number of tables still unreclaimed at the end of
</div><div id="l1908" class="code_block">garbage collection.
</div><div id="l1909" class="code_block">
</div><div id="l1910" class="code_block"><span class="nb">{</span><span class="k">\bf</span> Error Cases<span class="nb">}</span>
</div><div id="l1911" class="code_block"><span class="k">\bi</span>
</div><div id="l1912" class="code_block"><span class="k">\item</span> <span class="nb">{</span><span class="k">\tt</span> Number<span class="nb">}</span> is not a variable
</div><div id="l1913" class="code_block"><span class="k">\bi</span>
</div><div id="l1914" class="code_block"><span class="k">\item</span> 	<span class="nb">{</span><span class="k">\tt</span> type<span class="k">\_error</span>(variable)<span class="nb">}</span>
</div><div id="l1915" class="code_block"><span class="k">\ei</span>
</div><div id="l1916" class="code_block"><span class="k">\ei</span>
</div><div id="l1917" class="code_block">
</div><div id="l1918" class="code_block"><span class="c">% - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
</div><div id="l1919" class="code_block">
</div><div id="l1920" class="code_block"><span class="k">\ourstandarditem</span><span class="nb">{</span>delete<span class="k">\_return</span>(+TableEntryHandle,+ReturnHandle)<span class="nb">}{</span>delete<span class="k">\_returns</span>/2<span class="nb">}{</span>Tabling<span class="nb">}</span>
</div><div id="l1921" class="code_block"><span class="c">%</span>
</div><div id="l1922" class="code_block">Removes the answer indicated by <span class="k">\code</span><span class="nb">{</span>ReturnHandle<span class="nb">}</span> from the table
</div><div id="l1923" class="code_block">entry referenced by <span class="k">\code</span><span class="nb">{</span>TableEntryHandle<span class="nb">}</span>.  The value of each
</div><div id="l1924" class="code_block">argument should be obtained from some previous invocation of a
</div><div id="l1925" class="code_block">table-inspection predicate.
</div><div id="l1926" class="code_block">
</div><div id="l1927" class="code_block">This predicate is low-level so no error checking is done.  In <span class="k">\version</span>
</div><div id="l1928" class="code_block">, this predicate does not reclaim space for deleted returns, but
</div><div id="l1929" class="code_block">simply marks the returns as invalid.
</div><div id="l1930" class="code_block">
</div><div id="l1931" class="code_block"><span class="nb">{</span><span class="k">\em</span> Warning: <span class="nb">}</span> While useful for purposes such as tabled aggregation,
</div><div id="l1932" class="code_block"><span class="nb">{</span><span class="k">\tt</span> delete<span class="k">\_return</span>/2<span class="nb">}</span> can be difficult to use, both from an
</div><div id="l1933" class="code_block">implementation and semantic perspective.  
</div><div id="l1934" class="code_block">
</div><div id="l1935" class="code_block"><span class="c">% - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
</div><div id="l1936" class="code_block">
</div><div id="l1937" class="code_block"><span class="k">\ourstandarditem</span><span class="nb">{</span>invalidate<span class="k">\_tables\_for</span>(+DynamicPredGoal,+Mode)<span class="nb">}{</span>invalidate<span class="k">\_tables\_for</span>/2<span class="nb">}{</span>Tabling<span class="nb">}</span>
</div><div id="l1938" class="code_block"><span class="c">%</span>
</div><div id="l1939" class="code_block">This predicate supports invalidation of tables.  Tables may become
</div><div id="l1940" class="code_block">invalid if dynamic predicates on which they depend change, due to
</div><div id="l1941" class="code_block">asserts or retracts.  By default XSB does not change or delete tables
</div><div id="l1942" class="code_block">when they become invalid; it is the user&#39;s responsibility to know when
</div><div id="l1943" class="code_block">a table is no longer valid and to use the <span class="nb">{</span><span class="k">\tt</span> abolish<span class="k">\_table\_*</span><span class="nb">}</span>
</div><div id="l1944" class="code_block">primitives to delete any table when its contents become invalid.
</div><div id="l1945" class="code_block">
</div><div id="l1946" class="code_block">This predicate gives the XSB programmer some support in managing
</div><div id="l1947" class="code_block">tables and deleting them when they become invalid.  To use this
</div><div id="l1948" class="code_block">predicate, the user must have previously added clauses to the dynamic
</div><div id="l1949" class="code_block">predicate, <span class="nb">{</span><span class="k">\tt</span> invalidate<span class="k">\_table\_for</span>/2<span class="nb">}</span>.  That predicate should be
</div><div id="l1950" class="code_block">defined to take a goal for a dynamic predicate and a mode indicator
</div><div id="l1951" class="code_block">and abolish (some) tables (or table calls) that might depend on (any
</div><div id="l1952" class="code_block">instance of) that fact.  <span class="k">\\</span> <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1953" class="code_block">invalidate<span class="k">\_tables\_for</span>(+DynamicPredGoal),+Mode<span class="nb">}</span> simply backtracks
</div><div id="l1954" class="code_block">through calls to all unifying clauses of <span class="k">\\</span> <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1955" class="code_block">invalidate<span class="k">\_table\_for</span>(+DynamicPredGoal,+Mode)<span class="nb">}</span>.  The <span class="nb">{</span><span class="k">\tt</span> Mode<span class="nb">}</span>
</div><div id="l1956" class="code_block">indicator can be any term as long as the two predicates agree on how
</div><div id="l1957" class="code_block">they should be used.  The intention is that <span class="nb">{</span><span class="k">\tt</span> Mode<span class="nb">}</span> will be either
</div><div id="l1958" class="code_block">&#39;assert&#39; or &#39;retract&#39; indicating the kind of database change being
</div><div id="l1959" class="code_block">made.
</div><div id="l1960" class="code_block">
</div><div id="l1961" class="code_block">Consider a simple example of the use of these predicates: Assume the
</div><div id="l1962" class="code_block">definition of tabled predicate <span class="nb">{</span><span class="k">\tt</span> ptab/3<span class="nb">}</span> depends on dynamic predicate
</div><div id="l1963" class="code_block"><span class="nb">{</span><span class="k">\tt</span> qdyn/2<span class="nb">}</span>.  In this case, the user could initially call:
</div><div id="l1964" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1965" class="code_block">      :- assert((invalidate<span class="nb">_</span>table<span class="nb">_</span>for(qdyn(<span class="nb">_</span>,<span class="nb">_</span>),<span class="nb">_</span>) :-
</div><div id="l1966" class="code_block">                    abolish<span class="nb">_</span>table<span class="nb">_</span>pred(ptab(<span class="nb">_</span>,<span class="nb">_</span>,<span class="nb">_</span>)))).
</div><div id="l1967" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1968" class="code_block">to declare that when <span class="nb">{</span><span class="k">\tt</span> qdyn/2<span class="nb">}</span> changes (in any way), the table for <span class="nb">{</span><span class="k">\tt</span> ptab/3<span class="nb">}</span>
</div><div id="l1969" class="code_block">should be abolished.  Then each time a fact such as <span class="nb">{</span><span class="k">\tt</span> qdyn(A,B)<span class="nb">}</span> is
</div><div id="l1970" class="code_block">asserted to, or retracted from, <span class="nb">{</span><span class="k">\tt</span> qdyn/2<span class="nb">}</span>, the user could call
</div><div id="l1971" class="code_block"><span class="k">\begin</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1972" class="code_block">      :- invalidate<span class="nb">_</span>table<span class="nb">_</span>for(qdyn(A,B),<span class="nb">_</span>).
</div><div id="l1973" class="code_block"><span class="k">\end</span><span class="nb">{</span>verbatim<span class="nb">}</span>
</div><div id="l1974" class="code_block">
</div><div id="l1975" class="code_block">The user could use the hook mechanisms in XSB (Chapter~<span class="k">\ref</span><span class="nb">{</span>hooks<span class="nb">}</span>) to
</div><div id="l1976" class="code_block">automatically invoke <span class="k">\\</span> <span class="nb">{</span><span class="k">\tt</span> invalidate<span class="k">\_tables\_for</span><span class="nb">}</span> whenever <span class="nb">{</span><span class="k">\tt</span>
</div><div id="l1977" class="code_block">  assert<span class="nb">}</span> and/or <span class="nb">{</span><span class="k">\tt</span> retract<span class="nb">}</span> is called.
</div><div id="l1978" class="code_block">
</div><div id="l1979" class="code_block"><span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l1980" class="code_block">
</div><div id="l1981" class="code_block">
</div><div id="l1982" class="code_block"><span class="c">%==========================================================================</span>
</div><div id="l1983" class="code_block">
</div><div id="l1984" class="code_block"><span class="c">%%%</span>
</div><div id="l1985" class="code_block"><span class="c">%%% OLD JUNK</span>
</div><div id="l1986" class="code_block"><span class="c">%%%</span>
</div><div id="l1987" class="code_block">
</div><div id="l1988" class="code_block"><span class="k">\comment</span><span class="nb">{</span>
</div><div id="l1989" class="code_block">
</div><div id="l1990" class="code_block"><span class="c">%\ournewitem{table\_prop(?Pred\_indicator,+Type,?Old\_val,+New\_val)}{Tabling}</span>
</div><div id="l1991" class="code_block"><span class="c">%\index{\texttt{table\_prop/4}}</span>
</div><div id="l1992" class="code_block"><span class="c">%This predicate is described together with the following one.</span>
</div><div id="l1993" class="code_block">
</div><div id="l1994" class="code_block"><span class="c">%\ournewitem{table\_prop(?Pred\_indicator,+Type,-Value)}{Tabling}\index{\texttt{table\_prop/3}}</span>
</div><div id="l1995" class="code_block"><span class="c">%This predicate is used either to provide information about a table</span>
</div><div id="l1996" class="code_block"><span class="c">%property, or to reset one of properties to a particular value.  These</span>
</div><div id="l1997" class="code_block"><span class="c">%values can also be set by the table declarations in the source code.</span>
</div><div id="l1998" class="code_block"><span class="c">%{\tt table\_prop} provides a method for doing so without having to</span>
</div><div id="l1999" class="code_block"><span class="c">%recompile code.</span>
</div><div id="l2000" class="code_block"><span class="c">%</span>
</div><div id="l2001" class="code_block"><span class="c">%In previous versions {\tt table\_prop} was used to reset hash sizes for</span>
</div><div id="l2002" class="code_block"><span class="c">%calls and returns.  It is not used in \version, but is maintained since</span>
</div><div id="l2003" class="code_block"><span class="c">%in future versions {\tt table\_prop} may be used for other table</span>
</div><div id="l2004" class="code_block"><span class="c">%properties such as subgoal subsumption.</span>
</div><div id="l2005" class="code_block">
</div><div id="l2006" class="code_block"><span class="nb">}</span>
</div><div id="l2007" class="code_block">
</div><div id="l2008" class="code_block"><span class="c">%In \version\ the properties visible to the user are the call and return</span>
</div><div id="l2009" class="code_block"><span class="c">%hash sizes.  Each tabled predicate contains two types of hash tables.</span>
</div><div id="l2010" class="code_block"><span class="c">%A {\em call hash table} is used to find whether the variant of a call</span>
</div><div id="l2011" class="code_block"><span class="c">%to a tabled predicate has occurred before in the course of a</span>
</div><div id="l2012" class="code_block"><span class="c">%computation.  Each tabled call has a {\em return hash table} which is</span>
</div><div id="l2013" class="code_block"><span class="c">%used during a computation to determine whether a given return needs to</span>
</div><div id="l2014" class="code_block"><span class="c">%be added to the table.  Appropriate indexing for call and return</span>
</div><div id="l2015" class="code_block"><span class="c">%lookup, including proper hash table sizes, is crucial to good</span>
</div><div id="l2016" class="code_block"><span class="c">%performance.  </span>
</div><div id="l2017" class="code_block">
</div><div id="l2018" class="code_block"><span class="c">%Hash table sizes are non-negative integers denoting the number of</span>
</div><div id="l2019" class="code_block"><span class="c">%buckets in the hash table.  When {\tt Pred\_indicator} denotes a</span>
</div><div id="l2020" class="code_block"><span class="c">%tabled predicate, the predicate can take one of two modes depending on</span>
</div><div id="l2021" class="code_block"><span class="c">%its arity.  In {\tt table\_prop/4}, the {\tt New\_value} is provided by</span>
</div><div id="l2022" class="code_block"><span class="c">%the user and {\tt Old\_value} is unified with the precious value of</span>
</div><div id="l2023" class="code_block"><span class="c">%the table property.  In {\tt table\_prop/3} the present value of the </span>
</div><div id="l2024" class="code_block"><span class="c">%property is returned.</span>
</div><div id="l2025" class="code_block">
</div><div id="l2026" class="code_block"><span class="c">%Presently, the hash table sizes can only be reset when there are no tabled</span>
</div><div id="l2027" class="code_block"><span class="c">%calls to {\tt Pred\_indicator}.  This can be ensured by a call to </span>
</div><div id="l2028" class="code_block"><span class="c">%{\tt abolish\_table\_pred/1}</span>
</div><div id="l2029" class="code_block"><span class="c">%</span>
</div><div id="l2030" class="code_block"><span class="c">%Future versions of \ourprolog\ may include additional indexing</span>
</div><div id="l2031" class="code_block"><span class="c">%strategies as configurable table properties.</span>
</div><div id="l2032" class="code_block">
</div><div id="l2033" class="code_block"><span class="k">\comment</span><span class="nb">{</span>
</div><div id="l2034" class="code_block">
</div><div id="l2035" class="code_block">    Exceptions:
</div><div id="l2036" class="code_block">    <span class="k">\begin</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l2037" class="code_block"><span class="c">%    \item[{\tt table\_error}]</span>
</div><div id="l2038" class="code_block"><span class="c">%       Attempt to reset hash table size for predicate with tabled calls.</span>
</div><div id="l2039" class="code_block">    <span class="k">\item</span><span class="na">[{\tt table\_error}]</span>
</div><div id="l2040" class="code_block">        Argument 1 is not a tabled predicate.
</div><div id="l2041" class="code_block">    <span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l2042" class="code_block">
</div><div id="l2043" class="code_block"><span class="nb">}</span>
</div><div id="l2044" class="code_block"><span class="c">%\ounewitem{table\_copy(+From,-To)} \index{\texttt{table\_copy/2}}</span>
</div><div id="l2045" class="code_block"><span class="c">%Table copy provides an explicit mechanism for the user to reduce the</span>
</div><div id="l2046" class="code_block"><span class="c">%amount of copying into and out of a table.  {\tt table\_copy/2}</span>
</div><div id="l2047" class="code_block"><span class="c">%succeeds when {\tt From} is ground, and returns a copy of that</span>
</div><div id="l2048" class="code_block"><span class="c">%structure (or list) in the table space.  No copying of that structure</span>
</div><div id="l2049" class="code_block"><span class="c">%will be required when calls or returns containing it are tabled, and</span>
</div><div id="l2050" class="code_block"><span class="c">%no copying will be necessary when returns using it are resolved with</span>
</div><div id="l2051" class="code_block"><span class="c">%goals. </span>
</div><div id="l2052" class="code_block"><span class="c">%</span>
</div><div id="l2053" class="code_block"><span class="c">%For an example of the use of table copy, see Section~\ref{dcg_tabling}</span>
</div><div id="l2054" class="code_block">
</div><div id="l2055" class="code_block"><span class="k">\comment</span><span class="nb">{</span>
</div><div id="l2056" class="code_block">
</div><div id="l2057" class="code_block"><span class="c">%\ournewitem{breg\_retskel(+Breg,+Arity,-ReturnSkeleton,-SubgoalStructurePtr)}</span>
</div><div id="l2058" class="code_block"><span class="c">%\index{\texttt{breg\_retskel/4}}</span>
</div><div id="l2059" class="code_block"><span class="c">%If Breg is bound to a pointer to the tabling choice point and </span>
</div><div id="l2060" class="code_block"><span class="c">%Arity is bound to the arity of the predicate corresponding to </span>
</div><div id="l2061" class="code_block"><span class="c">%the choice point, {\tt breg\_retskel} succeeds after binding </span>
</div><div id="l2062" class="code_block"><span class="c">%{\tt ReturnSkeleton} to ret/n as in {\tt get\_calls/3} and </span>
</div><div id="l2063" class="code_block"><span class="c">%{\tt SubgoalStructurePtr} to the pointer to the subgoal structure.</span>
</div><div id="l2064" class="code_block">
</div><div id="l2065" class="code_block"><span class="c">%Warning:This built-in works for tabling predicates only.</span>
</div><div id="l2066" class="code_block">
</div><div id="l2067" class="code_block"><span class="nb">}</span>
</div><div id="l2068" class="code_block">
</div><div id="l2069" class="code_block"><span class="c">%========================================================</span>
</div><div id="l2070" class="code_block">
</div><div id="l2071" class="code_block"><span class="k">\end</span><span class="nb">{</span>description<span class="nb">}</span>
</div><div id="l2072" class="code_block">
</div><div id="l2073" class="code_block">
</div><div id="l2074" class="code_block">
</div><div id="l2075" class="code_block"><span class="c">%%% Local Variables: </span>
</div><div id="l2076" class="code_block"><span class="c">%%% mode: latex</span>
</div><div id="l2077" class="code_block"><span class="c">%%% TeX-master: &quot;manual1&quot;</span>
</div><div id="l2078" class="code_block"><span class="c">%%% End: </span>
</div></pre></div></td></tr></table></div>

      
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