From dc856223f5eab57d8a4881782ec0f50abd12afa3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ludovic=20Court=C3=A8s?= <ludo@gnu.org>
Date: Thu, 9 Nov 2017 23:31:18 +0100
Subject: ui: Add an 'unbound-variable' exception printer.

* guix/ui.scm (print-unbound-variable-error): New variable.
Use it as the 'unbound-variable' printer.
---
 guix/ui.scm | 12 ++++++++++++
 1 file changed, 12 insertions(+)

(limited to 'guix/ui.scm')

diff --git a/guix/ui.scm b/guix/ui.scm
index 9f790b6451..05782a537e 100644
--- a/guix/ui.scm
+++ b/guix/ui.scm
@@ -149,6 +149,18 @@ messages."
     (report-error args ...)
     (exit 1)))
 
+(define (print-unbound-variable-error port key args default-printer)
+  ;; Print unbound variable errors more nicely, and in the right language.
+  (match args
+    ((proc message (variable) _ ...)
+     ;; We can always omit PROC because when it's useful (i.e., different from
+     ;; "module-lookup"), it gets displayed before.
+     (format port (G_ "~a: unbound variable") variable))
+    (_
+     (default-printer))))
+
+(set-exception-printer! 'unbound-variable print-unbound-variable-error)
+
 (define (make-user-module modules)
   "Return a new user module with the additional MODULES loaded."
   ;; Module in which the machine description file is loaded.
-- 
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