enable meta_predicate/1 declarations

src/lib/assoc.pl

@@ -63,11 +63,8 @@ Assocs are Key-Value associations implemented as  a balanced binary tree
 @author         R.A.O'Keefe, L.Damas, V.S.Costa and Jan Wielemaker
 */
 
-/*
+:- meta_predicate map_assoc(1, ?).
-:- meta_predicate
+:- meta_predicate map_assoc(2, ?, ?).
-    map_assoc(1, ?),
-    map_assoc(2, ?, ?).
-*/
 
 %!  empty_assoc(?Assoc) is semidet.
 %