add preliminary support for DCGs.

src/prolog/lib/dcgs.pl

@@ -0,0 +1,66 @@
+:- module(dcgs, [(-->)/2, phrase/2, phrase/3]).
+
+:- use_module(library(lists), [append/3]).
+
+:- op(1200, xfx, -->).
+
+phrase(G, Ls0) :-
+    nonvar(G), G = [_|_], !, append(G, _, Ls0).
+phrase(G, Ls0) :-
+    nonvar(G), G = (G1, G2), !, phrase(G1, Ls0, Ls1), phrase(G2, Ls1).
+phrase(G, Ls0) :-
+    call(G, Ls0, _).
+
+phrase(G, Ls0, Ls1) :-
+    nonvar(G), G = [_|_], !, append(G, Ls1, Ls0).
+phrase(G, Ls0, Ls2) :-
+    nonvar(G), G = (G1, G2), !,
+    phrase(G1, Ls0, Ls1), phrase(G2, Ls1, Ls2).
+phrase(G, Ls0, Ls1) :-
+    call(G, Ls0, Ls1).
+
+term_expansion(Term0, (ModHead :- ModBody)) :-
+    nonvar(Term0),
+    Term0 = (Head, [SC | SCs] --> Body),
+    !,
+    nonvar(Head),
+    Head =.. [RuleName | Args],
+    append(Args, ['$VAR'(0), '$VAR'(N)], ModArgs),
+    ModHead =.. [RuleName | ModArgs],
+    nonvar(Body),
+    expand_body(Body, ModBody1, 0, N1),
+    expand_body_term([SC | SCs], ModBody2, N1, N),
+    ModBody = (ModBody1, ModBody2).
+term_expansion(Term0, (ModHead :- ModBody)) :-
+    nonvar(Term0),
+    Term0 = (Head --> Body),
+    nonvar(Head),
+    Head =.. [RuleName | Args],
+    append(Args, ['$VAR'(0), '$VAR'(N)], ModArgs),
+    ModHead =.. [RuleName | ModArgs],
+    nonvar(Body),
+    expand_body(Body, ModBody, 0, N).
+
+expand_body((Term, Terms), (ModTerm, ModTerms), N0, N) :-
+    !, expand_body_term(Term, ModTerm, N0, N1),
+    expand_body(Terms, ModTerms, N1, N).
+expand_body(Term, ModTerm, N0, N) :-
+    expand_body_term(Term, ModTerm, N0, N).
+
+expand_body_term([], true, N, N) :- !.
+expand_body_term([Arg|Args], ModTerm, N0, N) :-
+    !, N is N0 + 1,
+    append([Arg|Args], '$VAR'(N), ModArgs),
+    ModTerm = ('$VAR'(N0) = ModArgs).
+expand_body_term(CommaTerm, ModTerm, N, N) :-
+    CommaTerm =.. [{} | BodyTerms], !,
+    comma_ify(BodyTerms, ModTerm).
+expand_body_term(GrammarRule, ModTerm, N0, N) :-
+    GrammarRule =.. [Name | Args],
+    N is N0 + 1,
+    append(Args, ['$VAR'(N0), '$VAR'(N)], ModArgs),
+    ModTerm =.. [Name | ModArgs].
+
+comma_ify([Term], Term) :- !.
+comma_ify([Term | Args], (Term, Terms)) :-
+    comma_ify(Terms, Args).