From 0cec1f3df906e463d8f0d60fc14a2343b898d08a Mon Sep 17 00:00:00 2001
From: Eli Barzilay <eli@racket-lang.org>
Date: Wed, 6 May 2009 04:08:43 +0000
Subject: [PATCH] forgot the none binding

svn: r14728

original commit: 82d12675539895d277473b065f6ccb324a2f9775
---
 collects/framework/preferences.ss | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/collects/framework/preferences.ss b/collects/framework/preferences.ss
index 000e77b4..78904a57 100644
--- a/collects/framework/preferences.ss
+++ b/collects/framework/preferences.ss
@@ -76,6 +76,9 @@ the state transitions / contracts are:
 ;; this is used as a wrapped to deal with the problem that different procedures might be eq?.
 (define-struct pref-callback (cb))
 
+;; used to detect missing hash entries
+(define none (gensym 'none))
+
 ;; get : symbol -> any
 ;; return the current value of the preference `p'
 ;; exported