From 27883d274967c599f6fddd12711e30a1d7ab85c8 Mon Sep 17 00:00:00 2001
From: Matthew Flatt <mflatt@racket-lang.org>
Date: Mon, 6 Jan 2020 04:35:26 -0700
Subject: [PATCH] another repair to `bitwise-arithmetic-shift`/`ash` folding

Fuzz testing exposed a problem with the example

   (bitwise-arithmetic-shift-left -1 -1)

original commit: fc6f411ffc65f436d54979dfc0455ae771f3375d
---
 s/cp0.ss | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/s/cp0.ss b/s/cp0.ss
index d4464e8a61..a2f75207fe 100644
--- a/s/cp0.ss
+++ b/s/cp0.ss
@@ -2419,9 +2419,10 @@
             (and xval
                  yval
                  (let ([r (guard (c [#t #f]) (op xval yval))])
-                   (when r
-                     (residualize-seq '() (list x y) ctxt)
-                     `(quote ,r))))))
+                   (cond
+                    [r (residualize-seq '() (list x y) ctxt)
+                       `(quote ,r)]
+                    [else #f])))))
         (define-syntax define-inline-ash-op
           (syntax-rules ()
             [(_ op)