`history-transform' was returning '() at the end of a chain of

subproblems, instead of the value of `the-empty-history'.  This caused
the debugger to signal an error when walking past the end of the
history.

diff --git a/v7/src/runtime/histry.scm b/v7/src/runtime/histry.scm
index acdd5dc0eb59c0646a1567f00ef72a8ca9874f9d..8373f9a7316e225e40ecf7fab4785e1c3ff00492 100644 (file)
--- a/v7/src/runtime/histry.scm
+++ b/v7/src/runtime/histry.scm
@@ -1,6 +1,6 @@
 ;;; -*-Scheme-*-
 ;;;
-;;;    $Header: /Users/cph/tmp/foo/mit-scheme/mit-scheme/v7/src/runtime/histry.scm,v 13.45 1987/04/17 00:54:28 cph Exp $
+;;;    $Header: /Users/cph/tmp/foo/mit-scheme/mit-scheme/v7/src/runtime/histry.scm,v 13.46 1987/06/02 11:26:07 cph Exp $
 ;;;
 ;;;    Copyright (c) 1987 Massachusetts Institute of Technology
 ;;;
@@ -208,7 +208,7 @@
                    (delay
                     (let ((next (shallower-vertebra current)))
                       (if (eq? next history)
-                          '()
+                          the-empty-history
                           (loop next)))))
              '()))))