dcgs dcg.

1 files changed, 34 insertions, 1 deletions

diff --git a/inst/prelude.pl b/inst/prelude.pl
index 34e7853..54246ba 100644
--- a/inst/prelude.pl
+++ b/inst/prelude.pl
@@ -1,9 +1,13 @@
 member(X, [X|_]).
 member(X, [_|T]) :- member(X,T).
 
-append([], X, X).
+append([], [], []) :- !.
+append([], [H|T], [H|T]) :- !.
 append([X|T], Y, [X|TY]) :- append(T,Y,TY).
 
+list([]).
+list([_|_]).
+
 :- op(700, xfx, is),
    op(700, xfx, <),
    op(700, xfx, =<),
@@ -50,3 +54,32 @@ gcd(X,Y,R) :- zero(Y), !, R=X.
 gcd(X,Y,R) :- X1 is X mod Y, gcd(Y,X1,R).
 
 lcm(X,Y,R) :- gcd(X,Y,GCD), R is X*(Y/GCD).
+
+:- op(1200, xfx, -->).
+
+say([], SameState, SameState) :- !.
+say(Tokens, ParsedList, Rest) :-
+  append(Tokens, Rest, ParsedList).
+
+load_expansion(X --> Y, Xp :- Yp) :- !,
+  expand_phrasecall(X, Xp, S0, S),
+  expand_phrase(Y, Yp, S0, S).
+
+expand_phrase((A, B), (Ap, Bp), S0, S) :- !,
+  expand_phrase(A, Ap, S0, S1),
+  expand_phrase(B, Bp, S1, S).
+expand_phrase((A; B), (Ap; Bp), S0, S) :- !,
+  expand_phrase(A, Ap, S0, S),
+  expand_phrase(B, Bp, S0, S).
+expand_phrase(L, say(L, S0, S), S0, S) :- list(L), !.
+expand_phrase({X}, X, S, S) :- !.
+expand_phrase(!, !, S, S) :- !.
+expand_phrase(X, Xp, S0, S) :- expand_phrasecall(X, Xp, S0, S).
+
+expand_phrasecall(X, Xp, S0, S) :-
+  atom(X), !,
+  struct(Xp, X, [S0, S]).
+expand_phrasecall(X, Xp, S0, S) :- !,
+  struct(X, Id, Args),
+  append(Args, [S0, S], Args1),
+  struct(Xp, Id, Args1).