remove vestigial prolog/ directory (#444)

src/lib/freeze.pl

@@ -0,0 +1,28 @@
+:- module(freeze, [freeze/2]).
+
+:- use_module(library(atts)).
+:- use_module(library(dcgs)).
+
+:- attribute frozen/1.
+
+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]
+        ).
+verify_attributes(_, _, []).
+
+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)].
+