From 894c531f6c379d73caa6f7c69cc63ef2f398f681 Mon Sep 17 00:00:00 2001
From: Mike Sperber <sperber@deinprogramm.de>
Date: Sat, 15 Jan 2011 13:07:33 +0100
Subject: [PATCH] Make DMdA's fold more robust.

---
 collects/deinprogramm/DMdA.rkt | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/collects/deinprogramm/DMdA.rkt b/collects/deinprogramm/DMdA.rkt
index c8a524d9b4..c36ad846f6 100644
--- a/collects/deinprogramm/DMdA.rkt
+++ b/collects/deinprogramm/DMdA.rkt
@@ -429,7 +429,15 @@
       ((empty? lis) unit)
       ((pair? lis) 
        (combine (first lis)
-                (fold unit combine (rest lis)))))))
+                (fold unit combine (rest lis))))
+      (else
+       (raise
+	(make-exn:fail:contract
+	 (string->immutable-string
+	  (format "Argument zu fold keine Liste, sondern ~e; andere Argumente: ~e ~e"
+		  lis
+		  unit combine))
+	 (current-continuation-marks)))))))
 
 ;; This is copied from collects/lang/private/beginner-funs.ss
 ;; Test-suite support (require is really an effect