From dc21dc06718f65e8588149231d5bbf5cac5b46aa Mon Sep 17 00:00:00 2001
From: Brady McDonough <brady.mcd.codes@gmail.com>
Date: Mon, 5 Apr 2021 23:32:31 -0600
Subject: [PATCH] added (display-if-not)

---
 tk/listlogic.scm | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/tk/listlogic.scm b/tk/listlogic.scm
index 801db55..a1797b4 100644
--- a/tk/listlogic.scm
+++ b/tk/listlogic.scm
@@ -1,5 +1,6 @@
 (define-module (tk listlogic)
-  #:export (flatten
+  #:export (display-if-not
+            flatten
             lp&
             l&
             if-some
@@ -57,3 +58,14 @@
   (syntax-rules ()
     ((if-some-else $cond $else)
      (if $cond $cond $else))))
+
+;; Prints the message if condition is #f, otherwise prints nothing
+(define-syntax display-if-not
+  (syntax-rules ()
+    ((display-if-not $cond)
+     (syntax-error "Must provide a string to (display-if-not)"))
+    ((display-if-not $cond $message)
+     (begin (if (not $cond) (display $message))
+            (newline)))
+    ((display-if-not $cond . $messages)
+     (display-if-not $cond (string-concatenate/shared '$messages)))))