<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<!-- header_tag -->
<html lang="en">
<head>
<title>Scheme procedures as properties - GNU LilyPond Notation Reference</title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<meta name="description" content="GNU LilyPond Notation Reference">
<meta name="generator" content="makeinfo 4.11">
<link title="Top" rel="start" href="index.es.html#Top">
<link rel="up" href="Interfaces-for-programmers.es.html#Interfaces-for-programmers" title="Interfaces for programmers">
<link rel="prev" href="Contexts-for-programmers.es.html#Contexts-for-programmers" title="Contexts for programmers">
<link rel="next" href="TODO-moved-into-scheme.es.html#TODO-moved-into-scheme" title="TODO moved into scheme">
<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
<!--
Copyright (C) 1999--2007 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''.
-->
<meta http-equiv="Content-Style-Type" content="text/css">
<style type="text/css"><!--
pre.display { font-family:inherit }
pre.format { font-family:inherit }
pre.smalldisplay { font-family:inherit; font-size:smaller }
pre.smallformat { font-family:inherit; font-size:smaller }
pre.smallexample { font-size:smaller }
pre.smalllisp { font-size:smaller }
span.sc { font-variant:small-caps }
span.roman { font-family:serif; font-weight:normal; }
span.sansserif { font-family:sans-serif; font-weight:normal; }
hr { border:0; height:1; color: #000000; background-color: #000000; }
/* hr {
border: none;
height: 1px;
color: #666666;
background-color: #666666;
}
body {
border-left: 1px solid #666666;
border-right: 1px solid #666666;
color: #332d28;
margin-right: auto;
margin-left: auto;
width: 60em;
list-style-type: square;
font-family: Arial,Helvetica,sans-serif;
padding-right: 1em;
padding-left: 1em;
}
a {
border-bottom: 1px dashed #344242;
text-decoration: none;
color: #344242;
}
a:link {
text-decoration: none;
}
a:visited {
border-bottom: 1px dashed #666666;
color: #666666;
}
a:active {
border-bottom: 1px solid #00cccc;
color: #00cccc;
}
a:hover {
border-bottom: 1px solid #1d7b85;
color: #1d7b85;
}
blockquote {
border: 1px solid #cccccc;
padding: 3px;
width: 40em;
}
.node {
border-left: 1px solid #666666;
margin: -0.5em 0px 1em;
padding: 2px 1px 0px;
font-style: italic;
}
.node a {
border: none;
text-decoration: underline;
font-style: normal;
font-weight: bold;
}
.verbatim {
font-family: "Courier New",Courier,monospace;
}
.unnumberedsubsubsec {
font-size: large;
color: #1d7b85;
}
.subsubheading {
font-size: large;
color: #3b220d;
}
.contents {
border: 1px dashed #339999;
margin: 3px 2em;
list-style-type: square;
padding-right: 1em;
width: 40em;
background-color: #fcfff9;
}
.contents a {
border-bottom: 1px dashed #423d34;
text-decoration: none;
color: #423d34;
}
.contents a:visited {
border-bottom: 1px dashed #666666;
color: #666666;
}
.contents a:active {
border-bottom: 1px solid #f0d86d;
color: #f0d86d;
}
.contents a:hover {
border-bottom: 1px solid #3b220d;
color: #3b220d;
}
.menu {
border-left: 1px dashed #339999;
margin: 3px 2em 1em;
list-style-type: square;
padding-left: 1.4em;
width: 40em;
}
.unnumbered {
}
h2 {
font-size: x-large;
color: #1d7b85;
}
*/
--></style>
</head>
<BODY BGCOLOR=WHITE TEXT=BLACK>
<div class="node">
<p>
<a name="Scheme-procedures-as-properties"></a>
Next: <a rel="next" accesskey="n" href="TODO-moved-into-scheme.es.html#TODO-moved-into-scheme">TODO moved into scheme</a>,
Previous: <a rel="previous" accesskey="p" href="Contexts-for-programmers.es.html#Contexts-for-programmers">Contexts for programmers</a>,
Up: <a rel="up" accesskey="u" href="Interfaces-for-programmers.es.html#Interfaces-for-programmers">Interfaces for programmers</a>
<hr>
</div>
<h3 class="section">6.6 Scheme procedures as properties</h3>
<p>Properties (like thickness, direction, etc.) can be set at fixed values
with \override, e.g.
<pre class="example">\override Stem #'thickness = #2.0
</pre>
<p>Properties can also be set to a Scheme procedure,
<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="../15/lily-a603033b.ly">
<img align="middle"
border="0" src="../15/lily-a603033b.png" alt="[image of music]">
</a>
</p>
</blockquote>
<p class="noindent">In this case, the procedure is executed as soon as the value of the
property is requested during the formatting process.
<p>Most of the typesetting engine is driven by such callbacks.
Properties that typically use callbacks include
<dl>
<dt><code>stencil</code><dd> The printing routine, that constructs a drawing for the symbol
<br><dt><code>X-offset</code><dd> The routine that sets the horizontal position
<br><dt><code>X-extent</code><dd> The routine that computes the width of an object
</dl>
<p>The procedure always takes a single argument, being the grob.
<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>,
<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>
<p class="noindent">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>In fact, using a single procedure as property value is equivalent to
<pre class="example">(ly:make-simple-closure (ly:make-simple-closure (list <var>proc</var>)))
</pre>
<p class="noindent">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.
<!-- footer_tag --><br><hr>
<div class="node">
<p>
Next: <a rel="next" accesskey="n" href="TODO-moved-into-scheme.es.html#TODO-moved-into-scheme">TODO moved into scheme</a>,
Previous: <a rel="previous" accesskey="p" href="Contexts-for-programmers.es.html#Contexts-for-programmers">Contexts for programmers</a>,
Up: <a rel="up" accesskey="u" href="Interfaces-for-programmers.es.html#Interfaces-for-programmers">Interfaces for programmers</a>
</div>
<div style="background-color: #e8ffe8; padding: 2; border: #c0ffc0 1px solid;">
<p>
<font size="-1">
Esta página corresponde a LilyPond-2.11.57 (rama de desarrollo).
<br>
<address>
Informe de los fallos a través de la lista en español <a href="http://es.groups.yahoo.com/group/lilypond-es/">lilypond-es</a>, o en inglés a través de <a href="http://post.gmane.org/post.php?group=gmane.comp.gnu.lilypond.bugs">http://post.gmane.org/post.php?group=gmane.comp.gnu.lilypond.bugs</a>. </address>
<br>
Se agradecen las <a href="http://lilypond.org/web/devel/participating/documentation-adding">sugerencias para la documentación</a>.
</font>
</p>
</div>
</BODY></html>
