From 27d7ad1e87da6007a4a1123941114802a74615c3 Mon Sep 17 00:00:00 2001
From: Vincent St-Amour <stamourv@racket-lang.org>
Date: Fri, 1 Jul 2011 15:36:03 -0400
Subject: [PATCH] Have letrec build unions in canonical form.

---
 collects/typed-scheme/typecheck/tc-let-unit.rkt | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/collects/typed-scheme/typecheck/tc-let-unit.rkt b/collects/typed-scheme/typecheck/tc-let-unit.rkt
index 19560a2d4e..85807d7f25 100644
--- a/collects/typed-scheme/typecheck/tc-let-unit.rkt
+++ b/collects/typed-scheme/typecheck/tc-let-unit.rkt
@@ -166,7 +166,9 @@
                                                       (s:member x safe-bindings bound-identifier=?))
                                                    l)
                                            types-from-user
-                                           (map (λ (x) (make-Union (list x -Undefined)))
+                                           (map (λ (x) (make-Union (if (type<? x -Undefined)
+                                                                       (list x -Undefined)
+                                                                       (list -Undefined x))))
                                                 types-from-user)))))
                          names))
                    ;; types the user gave. check against that to error if we could get undefined