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loop combinator handles ambiguity. 

remove some old notes.
This commit is contained in:
Simon Forman 2019-08-04 09:28:01 -07:00
parent a3f863ff18
commit 0048ee212d
1 changed files with 7 additions and 25 deletions
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32
thun/thun.pl
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@ -223,6 +223,13 @@ combo(branch, [T, F, Expr|S], S, Ei, Eo) :-
combo(loop, [_, false|S], S, E, E ).
combo(loop, [B, true|S], S, Ei, Eo) :- append(B, [B, loop|Ei], Eo).
combo(loop, [B, Expr|S], S, Ei, Eo) :-
\+ Expr = true, \+ Expr = false,
catch( % Try Expr and do one or the other,
(Expr -> append(B, [B, loop|Ei], Eo) ; Ei=Eo),
_, % If Expr don't grok, try both branches.
(Ei=Eo ; append(B, [B, loop|Ei], Eo))
).
combo(step, [_, []|S], S, E, E ).
combo(step, [P, [X]|S], [X|S], Ei, Eo) :- !, append(P, Ei, Eo).
@ -309,28 +316,3 @@ to_fixed_point(DCG, Ei, Eo) :-
grow(Ei, Eo) :- to_fixed_point(rebo(expando, grow ), Ei, Eo).
shrink(Ei, Eo) :- to_fixed_point(rebo(contracto, shrink), Ei, Eo).
/*
?- E=[foo,bar,swap,cons,baz],phrase(shrink, E, ExprOut).
E = [foo, bar, swap, cons, baz],
ExprOut = [foo, bar, swons, baz].
?- E=[foo, bar, swons, baz],phrase(grow, E, ExprOut).
E = [foo, bar, swons, baz],
ExprOut = [foo, bar, swap, cons, baz].
*/
% ... --> [] | [_], ... .
% for the ellipsis operator
% http://swi-prolog.996271.n3.nabble.com/DCG-idioms-td3117.html which references:
% David B. Searls, Investigating the Linguistics of DNA with Definite Clause Grammars. NACLP 1989.
% phrase(expando, ExprIn, ExprOut).
% E=[foo,bar,swap,cons,baz],phrase((...,contracto,...), E, ExprOut).
% E = [foo, bar, swap, cons, baz],
% ExprOut = [swons, baz]