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pl:prolog:pllib:all_solutions [2019/06/27 15:50] (aktualna) |
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| + | ====== All solutions ====== | ||
| + | {{tag>searching knowledge_base}} | ||
| + | ===== Description ===== | ||
| + | Implementing an all-solutions predicate using difference-lists, assert and retract | ||
| + | |||
| + | **Source**: The Art of Prolog | ||
| + | ===== Download ===== | ||
| + | Program source code: {{all_solutions.pl}} | ||
| + | ===== Listing ===== | ||
| + | <code prolog> | ||
| + | /* | ||
| + | find_all_dl(X,Goal,Instances) :- Instances is the multiset | ||
| + | of instances of X for which Goal is true. The multiplicity | ||
| + | of an element is the number of different ways Goal can be | ||
| + | proved with it as an instance of X. | ||
| + | */ | ||
| + | :- op(40,xfx,\). | ||
| + | |||
| + | find_all_dl(X,Goal,Xs) :- | ||
| + | asserta('$instance'('$mark')), | ||
| + | Goal, | ||
| + | asserta('$instance'(X)), | ||
| + | fail. | ||
| + | find_all_dl(X,Goal,Xs\Ys) :- | ||
| + | retract('$instance'(X)), | ||
| + | reap(X,Xs\Ys), !. | ||
| + | |||
| + | reap(X,Xs\Ys) :- | ||
| + | X \== '$mark', | ||
| + | retract('$instance'(X1)), ! , | ||
| + | reap(X1,Xs\[X|Ys]). | ||
| + | reap('$mark',Xs\Xs). | ||
| + | |||
| + | % Program 16.3 : Implementing an all-solutions predicate using | ||
| + | % difference-lists, assert and retract | ||
| + | |||
| + | </code> | ||
| + | ===== Comments ===== | ||
