gensym builtin for SWI emulation.

git-svn-id: https://yap.svn.sf.net/svnroot/yap/trunk@1423 b08c6af1-5177-4d33-ba66-4b1c6b8b522a

library/gensym.yap

@@ -0,0 +1,24 @@
+:- module(gensym, [
+	gensym/2,
+	reset_gensym/1,
+	reset_gensym/0
+    ]).
+
+:- dynamic gensym_key/2.
+
+gensym(Atom, New) :-
+	retract(gensym_key(Atom,Id)), !,
+	atomic_concat(Atom,Id,New),
+	NId is Id+1,
+	assert(gensym_key(Atom,NId)).
+gensym(Atom, New) :-
+	atomic_concat(Atom,1,New),
+	assert(gensym_key(Atom,2)).
+
+reset_gensym(Atom) :-
+	retract(gensym_key(Atom,_)).
+
+reset_gensym :-
+	retractall(gensym_key(_,_)).
+
+