Don't allow event receivers to be added twice.

diff --git a/v7/src/runtime/events.scm b/v7/src/runtime/events.scm
index cc2f4b98c80870369b303a6d935901c487291386..327c614b05379ef7d3675936f1fa939762ecf7b1 100644 (file)
--- a/v7/src/runtime/events.scm
+++ b/v7/src/runtime/events.scm
@@ -1,8 +1,8 @@
 #| -*-Scheme-*-
 
-$Id: events.scm,v 14.4 1999/01/02 06:11:34 cph Exp $
+$Id: events.scm,v 14.5 2000/04/07 20:42:30 cph Exp $
 
-Copyright (c) 1988-1999 Massachusetts Institute of Technology
+Copyright (c) 1988-2000 Massachusetts Institute of Technology
 
 This program is free software; you can redistribute it and/or modify
 it under the terms of the GNU General Public License as published by
@@ -72,10 +72,13 @@ Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
                      ((null? receivers))
                    (apply (car receivers) (cdr event))))
                 ((ADD-RECEIVER)
-                 (set-event-distributor/receivers!
-                  event-distributor
-                  (append! (event-distributor/receivers event-distributor)
-                           (list (cdr event)))))
+                 (let ((receiver (cdr event))
+                       (receivers
+                        (event-distributor/receivers event-distributor)))
+                   (if (not (memv receiver receivers))
+                       (set-event-distributor/receivers!
+                        event-distributor
+                        (append! receivers (list receiver))))))
                 ((REMOVE-RECEIVER)
                  (set-event-distributor/receivers!
                   event-distributor