From 7d62bd9bf492a787674f042530a072a20de25ce0 Mon Sep 17 00:00:00 2001
From: Graham Percival <graham@percival-music.ca>
Date: Tue, 26 Dec 2006 07:07:21 -0800
Subject: [PATCH] Add info about music functions without arguments.

---
 .../user/programming-interface.itely          | 31 +++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/Documentation/user/programming-interface.itely b/Documentation/user/programming-interface.itely
index 1cadde8f2e..3909b5b65c 100644
--- a/Documentation/user/programming-interface.itely
+++ b/Documentation/user/programming-interface.itely
@@ -27,6 +27,7 @@ This section discusses how to create music functions within LilyPond.
 * Paired substitution functions::  
 * Mathematics in functions::    
 * Void functions::              
+* Functions without arguments::  
 * Overview of available music functions::  
 @end menu
 
@@ -237,6 +238,36 @@ noPointAndClick =
 \noPointAndClick   % disable point and click
 @end example
 
+
+@node Functions without arguments
+@subsection Functions without arguments
+
+In most cases a function without arguments should be written
+with an identifier,
+
+@example
+dolce = \markup@{ \italic \bold dolce @}
+@end example
+
+However, in rare cases it may be useful to create a music function
+without arguments,
+
+@example
+displayBarNum =
+#(define-music-function (parser location) ()
+   (if (eq? #t (ly:get-option display-bar-numbers))
+       #@{ \once \override Score.BarNumber #'break-visibility = ##f #@}
+       #@{#@}))
+@end example
+
+To actually display bar numbers where this function is called,
+invoke lilypond with
+
+@example
+lilypond -d display-bar-numbers FILENAME.ly
+@end example
+
+
 @node Overview of available music functions
 @subsection Overview of available music functions
 
-- 
2.39.5