From 206638e92bf98c5f954e3aa28e76f4a04e3889e3 Mon Sep 17 00:00:00 2001
From: Vitor Santos Costa <vsc@dcc.fc.up.pt>
Date: Fri, 24 Sep 2010 12:37:36 +0100
Subject: [PATCH] fix checking on_signal/3 (obs from Theo Mantadelis).

---
 pl/signals.yap | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/pl/signals.yap b/pl/signals.yap
index 1a925ff12..2ba46821e 100644
--- a/pl/signals.yap
+++ b/pl/signals.yap
@@ -210,6 +210,18 @@
 '$signal_def'(sig_alarm, true). 
 
 
+'$signal'(sig_hup).
+'$signal'(sig_usr1).
+'$signal'(sig_usr2).
+'$signal'(sig_pipe).
+'$signal'(sig_alarm).
+'$signal'(sig_vtalarm).
+
+on_signal(Signal,OldAction,NewAction) :-
+	var(Signal), !,
+	(nonvar(OldAction) -> throw(error(instantiation_error,on_signal/3)) ; true),
+        '$signal'(Signal),
+	on_signal(Signal, OldAction, NewAction).
 on_signal(Signal,OldAction,default) :-
 	'$reset_signal'(Signal, OldAction).
 on_signal(Signal,OldAction,Action) :-
@@ -219,7 +231,7 @@ on_signal(Signal,OldAction,Action) :-
 	Action = (_:Goal),
 	var(Goal), !,
 	'$check_signal'(Signal, OldAction),
-	Action = OldAction.
+	Goal = OldAction.
 on_signal(Signal,OldAction,Action) :-
 	'$reset_signal'(Signal, OldAction),
         % 13211-2 speaks only about callable