From: Stephen Adams <edu/mit/csail/zurich/adams>
Date: Thu, 27 Jul 1995 00:22:16 +0000 (+0000)
Subject: Arrange that GLOBAL_ENV is #F and END_OF_CHAIN is different for any
X-Git-Tag: 20090517-FFI~6131
X-Git-Url: https://birchwood-abbey.net/git?a=commitdiff_plain;h=a5545bcd010b6eb92693394a116c577d7d92daa4;p=mit-scheme.git

Arrange that GLOBAL_ENV is #F and END_OF_CHAIN is different for any
representation choice of #F.
---

diff --git a/v7/src/microcode/sdata.h b/v7/src/microcode/sdata.h
index 6667a55d0..18722792d 100644
--- a/v7/src/microcode/sdata.h
+++ b/v7/src/microcode/sdata.h
@@ -30,7 +30,7 @@ Technology nor of any adaptation thereof in any advertising,
 promotional, or sales literature without prior written consent from
 MIT in each case. */
 
-/* $Id: sdata.h,v 9.32 1993/06/24 07:09:46 gjr Exp $
+/* $Id: sdata.h,v 9.33 1995/07/27 00:22:16 adams Exp $
  *
  * Description of the user data objects.  This should parallel the
  * file SDATA.SCM in the runtime system.
@@ -212,10 +212,15 @@ MIT in each case. */
 /* An environment chain always ends in a pointer with type code
    of GLOBAL_ENV.  This will contain an address part which
    either indicates that the lookup should continue on to the
-   true global environment, or terminate at this frame. */
+   true global environment, or terminate at this frame.
 
-#define GO_TO_GLOBAL	0
-#define END_OF_CHAIN	1
+   We arrange for the global environment to be the same as #F, and the
+   end chain to be different by toggling the lowest bit:
+ */
+
+#define GLOBAL_ENV     (OBJECT_TYPE(SHARP_F))
+#define GO_TO_GLOBAL   (OBJECT_DATUM(SHARP_F))
+#define END_OF_CHAIN   ((GO_TO_GLOBAL) ^ 1)
 
 /* Environment extension objects: