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pl:prolog:pllib:evaluator [2019/06/27 15:50] (aktualna)
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 +====== Evaluator ======
 +{{tag>​math arithmetic}}
 +===== Description =====
 +Evaluator which traverses the structure of the evaluated term, where variables are represented by Prolog atoms like a, b or c, so they do not correspond to Prolog variables.
 +
 +**Source**: ​ Guide to Prolog Programming (on-line tutorial)
 +===== Download =====
 +Program source code: {{evaluator.pl}}
 +===== Listing =====
 +<code prolog>
 +eval(A+B,​CV):​-eval(A,​AV),​eval(B,​BV),​CV is AV+BV.
 +eval(A-B,​CV):​-eval(A,​AV),​eval(B,​BV),​CV is AV-BV.
 +eval(A*B,​CV):​-eval(A,​AV),​eval(B,​BV),​CV is AV*BV.
 +eval(Num,​Num):​-number(Num).
 +
 +eval_v(A+B,​CV,​Vars):​-eval_v(A,​AV,​Vars),​eval_v(B,​BV,​Vars),​CV is AV+BV.
 +eval_v(A-B,​CV,​Vars):​-eval_v(A,​AV,​Vars),​eval_v(B,​BV,​Vars),​CV is AV-BV.
 +eval_v(A*B,​CV,​Vars):​-eval_v(A,​AV,​Vars),​eval_v(B,​BV,​Vars),​CV is AV*BV.
 +eval_v(Num,​Num,​Vars):​-number(Num).
 +eval_v(Var,​Value,​Vars):​-atom(Var),​member(Var/​Value,​Vars).
 +
 +% Try ?​-eval_v(2*a+b,​Val,​[a/​1,​b/​5]) to test the above program.</​code>​
 +===== Comments =====
  
pl/prolog/pllib/evaluator.txt · ostatnio zmienione: 2019/06/27 15:50 (edycja zewnętrzna)
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