From 4b2c9cfbcc0fbff2c743202112137628ca202cc1 Mon Sep 17 00:00:00 2001
From: Tony Garnock-Jones <tonygarnockjones@gmail.com>
Date: Mon, 8 Jun 2015 10:30:13 -0400
Subject: [PATCH] Add exn->string, following the function of the same name in
 the web-server.

---
 pkgs/racket-doc/scribblings/reference/exns.scrbl | 12 ++++++++++++
 racket/collects/racket/exn.rkt                   | 10 ++++++++++
 2 files changed, 22 insertions(+)
 create mode 100644 racket/collects/racket/exn.rkt

diff --git a/pkgs/racket-doc/scribblings/reference/exns.scrbl b/pkgs/racket-doc/scribblings/reference/exns.scrbl
index 209f1b1095..ea26cdbddc 100644
--- a/pkgs/racket-doc/scribblings/reference/exns.scrbl
+++ b/pkgs/racket-doc/scribblings/reference/exns.scrbl
@@ -960,3 +960,15 @@ property, @racket[#f] otherwise.}
          (exn:missing-module? . -> . module-path?)]{
 
 Returns the @tech{module path}-getting procedure associated with @racket[v].}
+
+@;------------------------------------------------------------------------
+@section{Additional Exception Functions}
+
+@note-lib-only[racket/exn]
+
+@defproc[(exn->string [exn (or/c exn? any/c)]) string?]{
+
+Formats @racket[exn] as a string. If @racket[exn] is an @racket[exn?],
+collects and returns the output from the current
+@racket[(error-display-handler)]; otherwise, simply converts
+@racket[exn] to a string using @racket[(format "~s\n" exn)].}
diff --git a/racket/collects/racket/exn.rkt b/racket/collects/racket/exn.rkt
new file mode 100644
index 0000000000..7d8bc88df8
--- /dev/null
+++ b/racket/collects/racket/exn.rkt
@@ -0,0 +1,10 @@
+#lang racket/base
+
+(provide exn->string)
+
+(define (exn->string exn)
+  (if (exn? exn)
+      (parameterize ([current-error-port (open-output-string)])
+        ((error-display-handler) (exn-message exn) exn)
+        (get-output-string (current-error-port)))
+      (format "~s\n" exn)))