From 069797dc88e3b19e8656d3f7326ef57243ea2977 Mon Sep 17 00:00:00 2001
From: David Thompson <dthompson2@worcester.edu>
Date: Sat, 15 Aug 2015 23:12:02 -0400
Subject: ui: Add leave-if-false.

* shroud/ui.scm (leave-if-false): New procedure.
---
 shroud/ui.scm | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/shroud/ui.scm b/shroud/ui.scm
index bbe0f2a..2fb3708 100644
--- a/shroud/ui.scm
+++ b/shroud/ui.scm
@@ -25,6 +25,7 @@
             program-name
             show-version-and-exit
             leave
+            leave-if-false
             make-user-module
             load*
             shroud-main))
@@ -67,6 +68,11 @@ There is NO WARRANTY, to the extent permitted by law.~%"
   (newline)
   (exit 1))
 
+(define (leave-if-false obj error . args)
+  "Display error message defined by the ERROR string and ARGS if OBJ
+is #f."
+  (or obj (apply leave error args)))
+
 (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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