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pl:prolog:pllib:unification_2 [2019/06/27 15:50] (aktualna)
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 +====== Unification 2 ======
 +{{tag>​terms}}
 +===== Description =====
 +Unification with the occurs check
 +
 +**Source**: ​ The Art of Prolog
 +===== Download =====
 +Program source code: {{unification_2.pl}}
 +===== Listing =====
 +<code prolog>
 +/*
 +   ​unify(Term1,​Term2) :- Term1 and Term2 are unified with the occurs check.
 +*/
 +   ​unify(X,​Y) :-
 + var(X), var(Y), X=Y.
 +   ​unify(X,​Y) :-
 + var(X), nonvar(Y), not_occurs_in(X,​Y),​ X=Y.
 +   ​unify(X,​Y) :-
 + var(Y), nonvar(X), not_occurs_in(Y,​X),​ Y=X.
 +   ​unify(X,​Y) :-
 + nonvar(X), nonvar(Y), constant(X),​ constant(Y),​ X=Y.
 +   ​unify(X,​Y) :-
 + nonvar(X), nonvar(Y), compound(X),​ compound(Y),​ term_unify(X,​Y).
 +
 +   ​not_occurs_in(X,​Y) :-
 + var(Y), X \== Y.
 +   ​not_occurs_in(X,​Y) :- 
 + nonvar(Y), constant(Y).
 +   ​not_occurs_in(X,​Y) :-
 + nonvar(Y), compound(Y),​ functor(Y,​F,​N),​ not_occurs_in(N,​X,​Y).
 +
 +   ​not_occurs_in(N,​X,​Y) :-
 + N > 0, arg(N,​Y,​Arg),​ not_occurs_in(X,​Arg),​ N1 is N-1, 
 + not_occurs_in(N1,​X,​Y).
 +   ​not_occurs_in(0,​X,​Y).
 +
 +   ​term_unify(X,​Y) :-
 + functor(X,​F,​N),​ functor(Y,​F,​N),​ unify_args(N,​X,​Y).
 +
 +   ​unify_args(N,​X,​Y) :-
 + N > 0, unify_arg(N,​X,​Y),​ N1 is N-1, unify_args(N1,​X,​Y).
 +   ​unify_args(0,​X,​Y).
 +
 +   ​unify_arg(N,​X,​Y) :-
 + arg(N,​X,​ArgX),​ arg(N,​Y,​ArgY),​ unify(ArgX,​ArgY).
 +
 +%  Program 10.6    Unification with the occurs check
 +
 +</​code>​
 +===== Comments =====
  
pl/prolog/pllib/unification_2.txt · ostatnio zmienione: 2019/06/27 15:50 (edycja zewnętrzna)
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