From dabc5b302ebbc07ea9d116095550634eb515c74b Mon Sep 17 00:00:00 2001
From: Chris Hanson <org/chris-hanson/cph>
Date: Sun, 15 Apr 2018 19:16:38 -0700
Subject: [PATCH] Change guarantee to show context of error.

---
 src/runtime/boot.scm | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/runtime/boot.scm b/src/runtime/boot.scm
index 0a36e5200..7ac9cd8fd 100644
--- a/src/runtime/boot.scm
+++ b/src/runtime/boot.scm
@@ -403,9 +403,9 @@ USA.
       (set-predicate<=! p1 p2))))
 
 (define (guarantee predicate object #!optional caller)
-  (if (predicate object)
-      object
-      (error:not-a predicate object caller)))
+  (if (not (predicate object))
+      (error:not-a predicate object caller))
+  object)
 
 (define (error:not-a predicate object #!optional caller)
   (error:wrong-type-argument object (predicate-description predicate) caller))
-- 
2.25.1