From 2cf0ea0dbbd5a43a62dadb81948ee29898585dd7 Mon Sep 17 00:00:00 2001
From: Ludovic Courtès <ludo@gnu.org>
Date: Thu, 17 Jul 2014 15:40:06 +0200
Subject: gexp: Gracefully handle printing of gexps with spliced references.

* guix/gexp.scm (write-gexp): Wrap 'write' call in
  'false-if-exception'.
* tests/gexp.scm ("printer", "printer vs. ungexp-splicing"): New tests.
---
 guix/gexp.scm | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

(limited to 'guix/gexp.scm')

diff --git a/guix/gexp.scm b/guix/gexp.scm
index 260118affa..c9f6cbe99a 100644
--- a/guix/gexp.scm
+++ b/guix/gexp.scm
@@ -60,7 +60,12 @@
 (define (write-gexp gexp port)
   "Write GEXP on PORT."
   (display "#<gexp " port)
-  (write (apply (gexp-proc gexp) (gexp-references gexp)) port)
+
+  ;; Try to write the underlying sexp.  Now, this trick doesn't work when
+  ;; doing things like (ungexp-splicing (gexp ())) because GEXP's procedure
+  ;; tries to use 'append' on that, which fails with wrong-type-arg.
+  (false-if-exception
+   (write (apply (gexp-proc gexp) (gexp-references gexp)) port))
   (format port " ~a>"
           (number->string (object-address gexp) 16)))
 
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