Don't attempt to display the name of an undefined environment.

diff --git a/v7/src/edwin/debug.scm b/v7/src/edwin/debug.scm
index 2b7ff441270a6c4c61289588344cad84c986b844..dc5659ef95dc310a606970246484ab9fc4c067e0 100644 (file)
--- a/v7/src/edwin/debug.scm
+++ b/v7/src/edwin/debug.scm
@@ -1,6 +1,6 @@
 ;;; -*-Scheme-*-
 ;;;
-;;;    $Header: /Users/cph/tmp/foo/mit-scheme/mit-scheme/v7/src/edwin/debug.scm,v 1.1 1992/06/05 21:39:12 cph Exp $
+;;;    $Header: /Users/cph/tmp/foo/mit-scheme/mit-scheme/v7/src/edwin/debug.scm,v 1.2 1992/06/08 16:50:57 aragorn Exp $
 ;;;
 ;;;    Copyright (c) 1992 Massachusetts Institute of Technology
 ;;;
@@ -959,8 +959,11 @@ it has been renamed it will not be automatically deleted."
                           port)
             (newline port)
             (write (stack-frame/return-address frame) port))))
-    (newline port)
-    (show-environment-name (subproblem/environment subproblem) port)))
+    (let ((environment (subproblem/environment subproblem)))
+      (if (not (debugging-info/undefined-environment? environment))
+         (begin
+           (newline port)
+           (show-environment-name environment port))))))
 
 (define subexpression-marker
   (string->symbol "###"))