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pl:prolog:pllib:dcg_interpreter_counting_words [2019/06/27 15:50] (aktualna) |
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| + | ====== Dcg interpreter counting words ====== | ||
| + | {{tag>DCG interpreter counting}} | ||
| + | ===== Description ===== | ||
| + | A DCG interpreter that counts words | ||
| + | |||
| + | **Source**: The Art of Prolog | ||
| + | ===== Download ===== | ||
| + | Program source code: {{dcg_interpreter_counting_words.pl}} | ||
| + | ===== Listing ===== | ||
| + | <code prolog> | ||
| + | /* | ||
| + | parse(Start,Tokens,N) :- | ||
| + | The sequence of tokens Tokens, represented as a difference-list, | ||
| + | can be reached by applying the grammar rules defined by -->/2, | ||
| + | starting from Start, and N tokens are found. | ||
| + | */ | ||
| + | |||
| + | :- op( 800, xfx, -->). | ||
| + | :- op(40,xfx,\). | ||
| + | |||
| + | parse(A,Tokens,N) :- | ||
| + | nonterminal(A), A --> B, parse(B,Tokens,N). | ||
| + | parse((A,B),Tokens\Xs,N) :- | ||
| + | parse(A,Tokens\Tokens1,NA), parse(B,Tokens1\Xs,NB), | ||
| + | N is NA+NB. | ||
| + | |||
| + | parse(A,Tokens,N) :- terminals(A), connect(A,Tokens), length(A,N). | ||
| + | parse({A},Xs\Xs,0) :- A. | ||
| + | |||
| + | terminals(Xs) :- list(Xs). | ||
| + | |||
| + | list([]). | ||
| + | list([X|Xs]) :- list(Xs). | ||
| + | |||
| + | connect([ ],Xs\Xs). | ||
| + | connect([W|Ws],[W|Xs]\Ys) :- connect(Ws,Xs\Ys). | ||
| + | |||
| + | length([X|Xs],N) :- length(Xs,N1), N is N1+1. | ||
| + | length([],0). | ||
| + | |||
| + | % Program 19.5: A DCG interpreter that counts words | ||
| + | </code> | ||
| + | ===== Comments ===== | ||
