WIP

library/freeze.pl

@@ -1,48 +1,58 @@
-:- module(freeze, [
-	freeze/2,
-	frozen/2
-	]).
+:- module(freeze, [ freeze/2, frozen/2]).
+
+/** Provides the constraint `freeze/2`.
+*/
 
 :- use_module(library(atts)).
 :- use_module(library(dcgs)).
-:- use_module(library(lists, [flatten/2])).
 
 :- meta_predicate(freeze(-, 0)).
 :- attribute frozen/1.
 
-frozen(Term, Goal) :-
-	copy_term(Term, Term2, Gs),
-	Term = Term2,
-	flatten(Gs, Gs2),
-	list_to_conjunction(Gs2, Fresh),
-	Fresh = Goal.
-
-:- help(frozen(@term,-callable), [iso(false),desc('Unify Goal with the goal or conjunction of goals delayed on some attributed variable in Term.')]).
-
 verify_attributes(Var, Other, Goals) :-
-	get_atts(Var, frozen(Fa)), !,       % are we involved?
-	(   var(Other) ->                   % must be attributed then
-		(   get_atts(Other,  frozen(Fb)) % has a pending goal?
-		->  put_atts(Other,  frozen((Fb,Fa))) % rescue conjunction
-		;   put_atts(Other,  frozen(Fa)) % rescue the pending goal
-		),
-		Goals = []
-	;   Goals = [Fa]
-	).
+        get_atts(Var, frozen(Fa)), !,       % are we involved?
+        (   var(Other) ->                   % must be attributed then
+            (   get_atts(Other,  frozen(Fb)) % has a pending goal?
+            ->  put_atts(Other,  frozen((Fb,Fa))) % rescue conjunction
+            ;   put_atts(Other,  frozen(Fa)) % rescue the pending goal
+            ),
+            Goals = []
+        ;   Goals = [Fa]
+        ).
 verify_attributes(_, _, []).
 
-freeze(X, Goal) :-
-	var(X),
-	!,
-	put_atts(Fresh, frozen(Goal)),
-	Fresh = X.
-freeze(_, Goal) :-
-	Goal.
+%% freeze(Var, Goal)
+%
+%  Schedules Goal to be executed when Var is instantiated. This can
+%  be useful to observe the exact moment a variable becomes bound to a
+%  more concrete term, for example when creating animations of search
+%  processes. Higher-level constructs such as `phrase_from_file/2` can
+%  also be implemented with `freeze/2`, by scheduling a goal that
+%  reads additional data from a file as soon as it is needed.
 
-:- help(freeze(+var,:callable), [iso(false),desc('Delay the execution of Goal until Var is bound (i.e., is not a variable or attributed variable).')]).
+freeze(X, Goal) :-
+    put_atts(Fresh, frozen(Goal)),
+    Fresh = X.
 
 attribute_goals(Var) -->
     { get_atts(Var, frozen(Goals)),
       put_atts(Var, -frozen(_)) },
     [freeze(Var, Goals)].
 
+
+
+/** Provides the predicate `frozen/2`.
+*/
+
+:- use_module(library(lists)).
+
+frozen(Term, Goal) :-
+	copy_term(Term, Term2, Gs),
+	Term = Term2,
+	flatten(Gs, Gs2),
+	list_to_conjunction(Gs2, Fresh),
+	Fresh = Goal.
+
+:- help(freeze(+var,:callable), [iso(false),desc('Delay the execution of Goal until Var is bound (i.e., is not a variable or attributed variable).')]).
+:- help(frozen(@term,-callable), [iso(false),desc('Unify Goal with the goal or conjunction of goals delayed on some attributed variable in Term.')]).
+