<!-- header_tag -->
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html401/loose.dtd">
<html>
<!-- Copyright C 1999-2009 by the authors
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.1
or any later version published by the Free Software Foundation;
with no Invariant Sections.
A copy of the license is included in the section entitled "GNU
Free Documentation License".
-->
<!-- Created on December 15, 2009 by texi2html 1.82
texi2html was written by:
Lionel Cons <Lionel.Cons@cern.ch> (original author)
Karl Berry <karl@freefriends.org>
Olaf Bachmann <obachman@mathematik.uni-kl.de>
and many others.
Maintained by: Many creative people.
Send bugs and suggestions to <texi2html-bug@nongnu.org>
-->
<head>
<title>GNU LilyPond Notation Reference: 6.6 Scheme procedures as properties</title>
<meta name="description" content="GNU LilyPond Notation Reference: 6.6 Scheme procedures as properties">
<meta name="keywords" content="GNU LilyPond Notation Reference: 6.6 Scheme procedures as properties">
<meta name="resource-type" content="document">
<meta name="distribution" content="global">
<meta name="Generator" content="texi2html 1.82">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<link href="index.de.html#index" rel="start" title="GNU LilyPond — Notation Reference">
<link href="LilyPond-command-index.de.html#LilyPond-command-index" rel="index" title="F. LilyPond command index">
<link href="index_toc.de.html#SEC_Contents" rel="contents" title="Table of Contents">
<link href="index_abt.de.html#SEC_About" rel="help" title="About This Document">
<link href="Interfaces-for-programmers.de.html#Interfaces-for-programmers" rel="up" title="6. Interfaces for programmers">
<link href="LilyPond-index.de.html#LilyPond-index" rel="next" title="G. LilyPond index">
<link href="Running-a-function-on-all-layout-objects.de.html#Running-a-function-on-all-layout-objects" rel="previous" title="6.5.2 Running a function on all layout objects">
<link rel="stylesheet" type="text/css" title="Patrick McCarty's design" href="lilypond-mccarty.css">
<link rel="alternate stylesheet" type="text/css" href="lilypond.css" title="Andrew Hawryluk's design">
<link rel="alternate stylesheet" type="text/css" href="lilypond-blue.css" title="Kurt Kroon's blue design">
<!--[if lte IE 7]>
<link href="lilypond-ie-fixes.css" rel="stylesheet" type="text/css">
<![endif]-->
</head>
<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
<div id="main">
<a name="Scheme-procedures-as-properties"></a>
<table class="nav_table">
<tr><td valign="middle" align="left" colspan="1">[<a href="Interfaces-for-programmers.de.html#Interfaces-for-programmers" title="Beginning of this chapter or previous chapter"> << Interfaces for programmers </a>]</td><td valign="middle" align="center" colspan="3">[<a href="index.de.html#index" title="Cover (top) of document" rel="start">Top</a>][<a href="index_toc.de.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="LilyPond-command-index.de.html#LilyPond-command-index" title="Index" rel="index">Index</a>][<a href="index_abt.de.html#SEC_About" title="About (help)" rel="help"> ? </a>]</td><td valign="middle" align="right" colspan="1">[<a href="Literature-list.de.html#Literature-list" title="Next chapter"> Literature list >> </a>]</td></tr><tr><td valign="middle" align="left" colspan="2">[<a href="Running-a-function-on-all-layout-objects.de.html#Running-a-function-on-all-layout-objects" title="Previous section in reading order" accesskey="p" rel="previous"> < Running a function on all layout objects </a>]</td><td valign="middle" align="center" colspan="1">[<a href="Interfaces-for-programmers.de.html#Interfaces-for-programmers" title="Up section" accesskey="u" rel="up"> Up : Interfaces for programmers </a>]</td><td valign="middle" align="right" colspan="2">[<a href="Using-Scheme-code-instead-of-_005ctweak.de.html#Using-Scheme-code-instead-of-_005ctweak" title="Next section in reading order" accesskey="n" rel="next"> Using Scheme code instead of \tweak > </a>]</td></tr></table>
<a name="Scheme-procedures-as-properties"></a>
<h2 class="section">6.6 Scheme procedures as properties</h2>
<p>Properties (like thickness, direction, etc.) can be set at fixed values
with \override, e.g.
</p>
<blockquote><pre class="example">\override Stem #'thickness = #2.0
</pre></blockquote>
<p>Properties can also be set to a Scheme procedure,
</p>
<blockquote><pre class="verbatim">\override Stem #'thickness = #(lambda (grob)
(if (= UP (ly:grob-property grob 'direction))
2.0
7.0))
c b a g b a g b
</pre><p>
<a href="../1b/lily-df19cfe2.ly">
<img align="middle"
border="0"
src="../1b/lily-df19cfe2.png"
alt="[image of music]">
</a>
</p>
</blockquote>
<p>In this case, the procedure is executed as soon as the value of the
property is requested during the formatting process.
</p>
<p>Most of the typesetting engine is driven by such callbacks.
Properties that typically use callbacks include
</p>
<dl compact="compact">
<dt> <code>stencil</code></dt>
<dd><p> The printing routine, that constructs a drawing for the symbol
</p></dd>
<dt> <code>X-offset</code></dt>
<dd><p> The routine that sets the horizontal position
</p></dd>
<dt> <code>X-extent</code></dt>
<dd><p> The routine that computes the width of an object
</p></dd>
</dl>
<p>The procedure always takes a single argument, being the grob.
</p>
<p>If routines with multiple arguments must be called, the current grob
can be inserted with a grob closure. Here is a setting from
<code>AccidentalSuggestion</code>,
</p>
<blockquote><pre class="example">(X-offset .
,(ly:make-simple-closure
`(,+
,(ly:make-simple-closure
(list ly:self-alignment-interface::centered-on-x-parent))
,(ly:make-simple-closure
(list ly:self-alignment-interface::x-aligned-on-self)))))
</pre></blockquote>
<p>In this example, both <code>ly:self-alignment-interface::x-aligned-on-self</code> and
<code>ly:self-alignment-interface::centered-on-x-parent</code> are called
with the grob as argument. The results are added with the <code>+</code>
function. To ensure that this addition is properly executed, the whole
thing is enclosed in <code>ly:make-simple-closure</code>.
</p>
<p>In fact, using a single procedure as property value is equivalent to
</p>
<blockquote><pre class="example">(ly:make-simple-closure (ly:make-simple-closure (list <var>proc</var>)))
</pre></blockquote>
<p>The inner <code>ly:make-simple-closure</code> supplies the grob as argument
to <var>proc</var>, the outer ensures that result of the function is
returned, rather than the <code>simple-closure</code> object.
</p>
<hr size="6">
<table class="nav_table">
<tr><td valign="middle" align="left" colspan="1">[<a href="Interfaces-for-programmers.de.html#Interfaces-for-programmers" title="Beginning of this chapter or previous chapter"> << Interfaces for programmers </a>]</td><td valign="middle" align="center" colspan="3">[<a href="index.de.html#index" title="Cover (top) of document" rel="start">Top</a>][<a href="index_toc.de.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="LilyPond-command-index.de.html#LilyPond-command-index" title="Index" rel="index">Index</a>][<a href="index_abt.de.html#SEC_About" title="About (help)" rel="help"> ? </a>]</td><td valign="middle" align="right" colspan="1">[<a href="Literature-list.de.html#Literature-list" title="Next chapter"> Literature list >> </a>]</td></tr><tr><td valign="middle" align="left" colspan="2">[<a href="Running-a-function-on-all-layout-objects.de.html#Running-a-function-on-all-layout-objects" title="Previous section in reading order" accesskey="p" rel="previous"> < Running a function on all layout objects </a>]</td><td valign="middle" align="center" colspan="1">[<a href="Interfaces-for-programmers.de.html#Interfaces-for-programmers" title="Up section" accesskey="u" rel="up"> Up : Interfaces for programmers </a>]</td><td valign="middle" align="right" colspan="2">[<a href="Using-Scheme-code-instead-of-_005ctweak.de.html#Using-Scheme-code-instead-of-_005ctweak" title="Next section in reading order" accesskey="n" rel="next"> Using Scheme code instead of \tweak > </a>]</td></tr></table>
<!-- footer_tag -->
<div class="footer">
<p class="footer_version">
This page is for LilyPond-2.12.3 (stable-branch).
</p>
<p class="footer_report">
Your <a href="http://lilypond.org/web/devel/participating/documentation-adding">suggestions for the documentation</a> are welcome, please report errors to our <a href="http://post.gmane.org/post.php?group=gmane.comp.gnu.lilypond.bugs">bug list</a>.
</p>
</div>
<p id="languages">
Other languages: <a href="Scheme-procedures-as-properties.es.html">español</a>.
<br>
</p>
<!-- FOOTER -->
<!-- end div#main here -->
</div>
<div id="tocframe">
<p class="toc_uplink"><a href="../index.de.html"
title="Documentation Index"><< Back to Documentation Index</a></p>
<h4 class="toc_header"> <a href="index.de.html#index" title="Start of the manual">Notation Reference</a></h4>
<div class="contents">
<ul class="toc">
<li><a name="toc-Musical-notation-1" href="Musical-notation.de.html#Musical-notation">1. Musical notation</a>
<ul class="toc">
<li><a name="toc-Pitches-1" href="Pitches.de.html#Pitches">1.1 Pitches</a> </li>
<li><a name="toc-Rhythms-1" href="Rhythms.de.html#Rhythms">1.2 Rhythms</a> </li>
<li><a name="toc-Expressive-marks-1" href="Expressive-marks.de.html#Expressive-marks">1.3 Expressive marks</a> </li>
<li><a name="toc-Repeats-1" href="Repeats.de.html#Repeats">1.4 Repeats</a> </li>
<li><a name="toc-Simultaneous-notes-1" href="Simultaneous-notes.de.html#Simultaneous-notes">1.5 Simultaneous notes</a> </li>
<li><a name="toc-Staff-notation-1" href="Staff-notation.de.html#Staff-notation">1.6 Staff notation</a> </li>
<li><a name="toc-Editorial-annotations-1" href="Editorial-annotations.de.html#Editorial-annotations">1.7 Editorial annotations</a> </li>
<li><a name="toc-Text-1" href="Text.de.html#Text">1.8 Text</a> </li>
</ul>
</li>
<li><a name="toc-Specialist-notation-1" href="Specialist-notation.de.html#Specialist-notation">2. Specialist notation</a>
<ul class="toc">
<li><a name="toc-Vocal-music-1" href="Vocal-music.de.html#Vocal-music">2.1 Vocal music</a> </li>
<li><a name="toc-Keyboard-and-other-multi_002dstaff-instruments-1" href="Keyboard-and-other-multi_002dstaff-instruments.de.html#Keyboard-and-other-multi_002dstaff-instruments">2.2 Keyboard and other multi-staff instruments</a> </li>
<li><a name="toc-Unfretted-string-instruments-1" href="Unfretted-string-instruments.de.html#Unfretted-string-instruments">2.3 Unfretted string instruments</a> </li>
<li><a name="toc-Fretted-string-instruments-1" href="Fretted-string-instruments.de.html#Fretted-string-instruments">2.4 Fretted string instruments</a> </li>
<li><a name="toc-Percussion-1" href="Percussion.de.html#Percussion">2.5 Percussion</a> </li>
<li><a name="toc-Wind-instruments-1" href="Wind-instruments.de.html#Wind-instruments">2.6 Wind instruments</a> </li>
<li><a name="toc-Chord-notation-1" href="Chord-notation.de.html#Chord-notation">2.7 Chord notation</a> </li>
<li><a name="toc-Ancient-notation-1" href="Ancient-notation.de.html#Ancient-notation">2.8 Ancient notation</a> </li>
<li><a name="toc-World-music-1" href="World-music.de.html#World-music">2.9 World music</a> </li>
</ul>
</li>
<li><a name="toc-General-input-and-output-1" href="General-input-and-output.de.html#General-input-and-output">3. General input and output</a>
<ul class="toc">
<li><a name="toc-Input-structure-1" href="Input-structure.de.html#Input-structure">3.1 Input structure</a> </li>
<li><a name="toc-Titles-and-headers-1" href="Titles-and-headers.de.html#Titles-and-headers">3.2 Titles and headers</a> </li>
<li><a name="toc-Working-with-input-files-1" href="Working-with-input-files.de.html#Working-with-input-files">3.3 Working with input files</a> </li>
<li><a name="toc-Controlling-output-1" href="Controlling-output.de.html#Controlling-output">3.4 Controlling output</a> </li>
<li><a name="toc-MIDI-output-1" href="MIDI-output.de.html#MIDI-output">3.5 MIDI output</a> </li>
</ul>
</li>
<li><a name="toc-Spacing-issues-1" href="Spacing-issues.de.html#Spacing-issues">4. Spacing issues</a>
<ul class="toc">
<li><a name="toc-Paper-and-pages-1" href="Paper-and-pages.de.html#Paper-and-pages">4.1 Paper and pages</a> </li>
<li><a name="toc-Music-layout-1" href="Music-layout.de.html#Music-layout">4.2 Music layout</a> </li>
<li><a name="toc-Breaks-1" href="Breaks.de.html#Breaks">4.3 Breaks</a> </li>
<li><a name="toc-Vertical-spacing-1" href="Vertical-spacing.de.html#Vertical-spacing">4.4 Vertical spacing</a> </li>
<li><a name="toc-Horizontal-spacing-1" href="Horizontal-spacing.de.html#Horizontal-spacing">4.5 Horizontal spacing</a> </li>
<li><a name="toc-Fitting-music-onto-fewer-pages-1" href="Fitting-music-onto-fewer-pages.de.html#Fitting-music-onto-fewer-pages">4.6 Fitting music onto fewer pages</a> </li>
</ul>
</li>
<li><a name="toc-Changing-defaults-1" href="Changing-defaults.de.html#Changing-defaults">5. Changing defaults</a>
<ul class="toc">
<li><a name="toc-Interpretation-contexts-1" href="Interpretation-contexts.de.html#Interpretation-contexts">5.1 Interpretation contexts</a> </li>
<li><a name="toc-Explaining-the-Internals-Reference-1" href="Explaining-the-Internals-Reference.de.html#Explaining-the-Internals-Reference">5.2 Explaining the Internals Reference</a> </li>
<li><a name="toc-Modifying-properties-1" href="Modifying-properties.de.html#Modifying-properties">5.3 Modifying properties</a> </li>
<li><a name="toc-Useful-concepts-and-properties-1" href="Useful-concepts-and-properties.de.html#Useful-concepts-and-properties">5.4 Useful concepts and properties</a> </li>
<li><a name="toc-Advanced-tweaks-1" href="Advanced-tweaks.de.html#Advanced-tweaks">5.5 Advanced tweaks</a> </li>
</ul>
</li>
<li class="toc_current"><a name="toc-Interfaces-for-programmers-1" href="Interfaces-for-programmers.de.html#Interfaces-for-programmers">6. Interfaces for programmers</a>
<ul class="toc">
<li><a name="toc-Music-functions-1" href="Music-functions.de.html#Music-functions">6.1 Music functions</a> </li>
<li><a name="toc-Programmer-interfaces-1" href="Programmer-interfaces.de.html#Programmer-interfaces">6.2 Programmer interfaces</a> </li>
<li><a name="toc-Building-complicated-functions-1" href="Building-complicated-functions.de.html#Building-complicated-functions">6.3 Building complicated functions</a> </li>
<li><a name="toc-Markup-programmer-interface-1" href="Markup-programmer-interface.de.html#Markup-programmer-interface">6.4 Markup programmer interface</a> </li>
<li><a name="toc-Contexts-for-programmers-1" href="Contexts-for-programmers.de.html#Contexts-for-programmers">6.5 Contexts for programmers</a> </li>
<li class="toc_current"><a name="toc-Scheme-procedures-as-properties-1" href="Scheme-procedures-as-properties.de.html#Scheme-procedures-as-properties">6.6 Scheme procedures as properties</a> </li>
<li><a name="toc-Using-Scheme-code-instead-of-_005ctweak-1" href="Using-Scheme-code-instead-of-_005ctweak.de.html#Using-Scheme-code-instead-of-_005ctweak">6.7 Using Scheme code instead of <code>\tweak</code></a> </li>
<li><a name="toc-Difficult-tweaks-1" href="Difficult-tweaks.de.html#Difficult-tweaks">6.8 Difficult tweaks</a> </li>
</ul>
</li>
<li><a name="toc-Literature-list-1" href="Literature-list.de.html#Literature-list">A. Literature list</a> </li>
<li><a name="toc-Notation-manual-tables-1" href="Notation-manual-tables.de.html#Notation-manual-tables">B. Notation manual tables</a>
<ul class="toc">
<li><a name="toc-Chord-name-chart-1" href="Chord-name-chart.de.html#Chord-name-chart">B.1 Chord name chart</a> </li>
<li><a name="toc-Common-chord-modifiers-1" href="Common-chord-modifiers.de.html#Common-chord-modifiers">B.2 Common chord modifiers</a> </li>
<li><a name="toc-Predefined-fretboard-diagrams-1" href="Predefined-fretboard-diagrams.de.html#Predefined-fretboard-diagrams">B.3 Predefined fretboard diagrams</a> </li>
<li><a name="toc-MIDI-instruments-1" href="MIDI-instruments.de.html#MIDI-instruments">B.4 MIDI instruments</a> </li>
<li><a name="toc-List-of-colors-1" href="List-of-colors.de.html#List-of-colors">B.5 List of colors</a> </li>
<li><a name="toc-The-Feta-font-1" href="The-Feta-font.de.html#The-Feta-font">B.6 The Feta font</a> </li>
<li><a name="toc-Note-head-styles-1" href="Note-head-styles.de.html#Note-head-styles">B.7 Note head styles</a> </li>
<li><a name="toc-Text-markup-commands-1" href="Text-markup-commands.de.html#Text-markup-commands">B.8 Text markup commands</a> </li>
<li><a name="toc-Text-markup-list-commands-1" href="Text-markup-list-commands.de.html#Text-markup-list-commands">B.9 Text markup list commands</a> </li>
<li><a name="toc-List-of-articulations-1" href="List-of-articulations.de.html#List-of-articulations">B.10 List of articulations</a> </li>
<li><a name="toc-Percussion-notes-1" href="Percussion-notes.de.html#Percussion-notes">B.11 Percussion notes</a> </li>
<li><a name="toc-All-context-properties-1" href="All-context-properties.de.html#All-context-properties">B.12 All context properties</a> </li>
<li><a name="toc-Layout-properties-1" href="Layout-properties.de.html#Layout-properties">B.13 Layout properties</a> </li>
<li><a name="toc-Identifiers-1" href="Identifiers.de.html#Identifiers">B.14 Identifiers</a> </li>
<li><a name="toc-Scheme-functions-1" href="Scheme-functions.de.html#Scheme-functions">B.15 Scheme functions</a> </li>
</ul>
</li>
<li><a name="toc-Cheat-sheet-1" href="Cheat-sheet.de.html#Cheat-sheet">C. Cheat sheet</a> </li>
<li><a name="toc-LilyPond-grammar-1" href="LilyPond-grammar.de.html#LilyPond-grammar">D. LilyPond grammar</a> </li>
<li><a name="toc-GNU-Free-Documentation-License-1" href="GNU-Free-Documentation-License.de.html#GNU-Free-Documentation-License">E. GNU Free Documentation License</a> </li>
<li><a name="toc-LilyPond-command-index-1" href="LilyPond-command-index.de.html#LilyPond-command-index">F. LilyPond command index</a> </li>
<li><a name="toc-LilyPond-index-1" href="LilyPond-index.de.html#LilyPond-index">G. LilyPond index</a> </li>
</ul>
</div>
</div>
</body>
</html>
