From ffad42a1b7ac60ed236c74d43217b25aeed02fe7 Mon Sep 17 00:00:00 2001
From: Chris Hanson <org/chris-hanson/cph>
Date: Tue, 2 Jun 1987 11:26:07 +0000
Subject: [PATCH] `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.

---
 v7/src/runtime/histry.scm | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/v7/src/runtime/histry.scm b/v7/src/runtime/histry.scm
index acdd5dc0e..8373f9a73 100644
--- 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)))))
 	      '()))))
 
-- 
2.25.1