68 lines
2.1 KiB
Prolog
68 lines
2.1 KiB
Prolog
:- module(dcgs, [(-->)/2, phrase/2, phrase/3]).
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:- use_module(library(lists), [append/3]).
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:- op(1200, xfx, -->).
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phrase(G, Ls0) :-
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nonvar(G), G = [_|_], !, append(G, _, Ls0).
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phrase(G, Ls0) :-
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nonvar(G), G = (G1, G2), !, phrase(G1, Ls0, Ls1), phrase(G2, Ls1).
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phrase(G, Ls0) :-
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call(G, Ls0, []).
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phrase(G, Ls0, Ls1) :-
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nonvar(G), G = [_|_], !, append(G, Ls1, Ls0).
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phrase(G, Ls0, Ls2) :-
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nonvar(G), G = (G1, G2), !,
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phrase(G1, Ls0, Ls1), phrase(G2, Ls1, Ls2).
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phrase(G, Ls0, Ls1) :-
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call(G, Ls0, Ls1).
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term_expansion(Term0, (ModHead :- ModBody)) :-
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nonvar(Term0),
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Term0 = (Head, [SC | SCs] --> Body),
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!,
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nonvar(Head),
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Head =.. [RuleName | Args],
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append(Args, ['$VAR'(0), '$VAR'(N)], ModArgs), %% problematic line.
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ModHead =.. [RuleName | ModArgs],
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nonvar(Body),
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expand_body(Body, ModBody1, 0, N1),
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expand_body_term([SC | SCs], ModBody2, N1, N),
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ModBody = (ModBody1, ModBody2).
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term_expansion(Term0, (ModHead :- ModBody)) :-
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nonvar(Term0),
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Term0 = (Head --> Body),
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nonvar(Head),
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Head =.. [RuleName | Args],
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append(Args, ['$VAR'(0), '$VAR'(N)], ModArgs),
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ModHead =.. [RuleName | ModArgs],
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nonvar(Body),
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expand_body(Body, ModBody, 0, N).
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expand_body(Term0, (ModTerm, ModTerms), N0, N) :-
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nonvar(Term0), Term0 = (Term, Terms), !,
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expand_body_term(Term, ModTerm, N0, N1),
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expand_body(Terms, ModTerms, N1, N).
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expand_body(Term0, ModTerm, N0, N) :-
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nonvar(Term0), expand_body_term(Term0, ModTerm, N0, N).
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expand_body_term([], true, N, N) :- !.
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expand_body_term([Arg|Args], ModTerm, N0, N) :-
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!, N is N0 + 1,
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append([Arg|Args], '$VAR'(N), ModArgs),
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ModTerm = ('$VAR'(N0) = ModArgs).
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expand_body_term(CommaTerm, ModTerm, N, N) :-
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CommaTerm =.. [{} | BodyTerms], !,
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comma_ify(BodyTerms, ModTerm).
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expand_body_term(GrammarRule, ModTerm, N0, N) :-
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GrammarRule =.. [Name | Args],
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N is N0 + 1,
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append(Args, ['$VAR'(N0), '$VAR'(N)], ModArgs),
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ModTerm =.. [Name | ModArgs].
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comma_ify([Term], Term) :- !.
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comma_ify([Term | Args], (Term, Terms)) :-
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comma_ify(Terms, Args).
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