From f85d18aed67965d8f8f5f7f80fc04360522afb52 Mon Sep 17 00:00:00 2001
From: Matthew Flatt <mflatt@racket-lang.org>
Date: Tue, 1 Jan 2019 13:58:48 -0700
Subject: [PATCH] io: fix printing of '||

---
 pkgs/racket-test-core/tests/racket/print.rktl |  1 +
 racket/src/io/print/symbol.rkt                | 11 +++++++++--
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/pkgs/racket-test-core/tests/racket/print.rktl b/pkgs/racket-test-core/tests/racket/print.rktl
index b9fb7e03cd..d475a7c70a 100644
--- a/pkgs/racket-test-core/tests/racket/print.rktl
+++ b/pkgs/racket-test-core/tests/racket/print.rktl
@@ -60,6 +60,7 @@
   (ptest "#\\x" #\x)
   (ptest "'apple" 'apple)
   (ptest "'|apple banana|" '|apple banana|)
+  (ptest "'||" '||)
   (ptest "'#:apple" '#:apple)
   (ptest "\"apple\"" "apple")
   (ptest "#\"apple\"" #"apple")
diff --git a/racket/src/io/print/symbol.rkt b/racket/src/io/print/symbol.rkt
index f1bc8b4b9f..9d97a35a5f 100644
--- a/racket/src/io/print/symbol.rkt
+++ b/racket/src/io/print/symbol.rkt
@@ -56,12 +56,19 @@
      (cond
        [(or for-keyword?
             for-type?
-            (not (string->number? str)))
+            (and (not (string->number? str))
+                 (not (string=? str ""))))
         str]
        ;; Remaining two cases add some form of quoting to
        ;; protect against a symbol looking like a number
        [(and config (not (config-get config read-accept-bar-quote)))
-        (string-append "\\" str)]
+        (cond
+          [(string=? str "")
+           ;; There's no good answer in this case. Traditionally, Racket
+           ;; just prints an empty string, anyway.
+           str]
+          [else
+           (string-append "\\" str)])]
        [else
         (string-append "|" str "|")])]
     [(or (and config (not (config-get config read-accept-bar-quote)))