add call_residue_vars (SWI and SICStus 4 compatibility).

docs/yap.tex

@@ -12097,6 +12097,23 @@ no
 The system only reports one invocation of @code{dif/2} as having
 suspended. 
 
+@item call_residue_vars(:@var{G},@var{L})
+@findex call_residue_vars/2
+@syindex call_residue_vars/2
+@cnindex call_residue_vars/2
+
+Call goal @var{G} and unify @var{L} with a list of all constrained variables created @emph{during} execution of @var{G}:
+
+@example
+  ?- dif(X,Z), call_residue_vars(dif(X,Y),L).
+dif(X,Z), call_residue_vars(dif(X,Y),L).
+L = [Y],
+dif(X,Z),
+dif(X,Y) ? ;
+
+no
+@end example
+
 @end table
 
 @node Attributed Variables, CLPR, Co-routining, Extensions

pl/corout.yap

@@ -560,6 +560,29 @@ frozen(V, LG) :-
 	'$fetch_same_done_goals'(G0, D0, LV, GF).
 
 
+call_residue_vars(Goal,Residue) :-
+	attributes:all_attvars(Vs0),
+	call(Goal),
+	attributes:all_attvars(Vs),
+	% this should not be actually strictly necessary right now.
+	% but it makes it a safe bet.
+	sort(Vs, Vss),
+	sort(Vs0, Vs0s),
+	'$ord_remove'(Vss, Vs0s, Residue).
+
+'$ord_remove'([], _, []).
+'$ord_remove'([V|Vs], [], [V|Vs]).
+'$ord_remove'([V1|Vss], [V2|Vs0s], Residue) :-
+	( V1 == V2 ->
+	  '$ord_remove'(Vss, Vs0s, Residue)
+	;
+	  V1 @< V2 ->
+	  Residue = [V1|ResidueF],
+	  '$ord_remove'(Vss, [V2|Vs0s], ResidueF)
+	;
+	  '$ord_remove'([V1|Vss], Vs0s, Residue)
+	).
+
 call_residue(Goal,Residue) :-
 	var(Goal), !,
 	'$do_error'(instantiation_error,call_residue(Goal,Residue)).

pl/modules.yap

@@ -512,6 +512,7 @@ source_module(Mod) :-
 	call_cleanup(:,:),
 	call_cleanup(:,?,:),
 	call_residue(:,?),
+	call_residue_vars(:,?),
 	catch(:,+,:),
 	clause(:,?),
 	clause(:,?,?),