contents/glyph/book/text_editing/macro_composition.html
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title: "Glyph - Macro Composition"
content-type: page
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<p>Glyph macros can be <em>composed</em> with other using the <code>/</code> character. Macro composition can be used
instead of nesting, provided that macro containers (also called <em>dispatchers</em> in certain situations) take only
one parameter and no attributes.</p>
<p>For example, the following code:</p>
<div class="CodeRay">
<div class="code">
<pre><span class="line-numbers"><a href="#n1" name="n1">1</a></span>?[
<span class="line-numbers"><a href="#n2" name="n2">2</a></span> not[output?[pdf]]|
<span class="line-numbers"><a href="#n3" name="n3">3</a></span> ...
<span class="line-numbers"><a href="#n4" name="n4">4</a></span>]</pre>
</div>
</div>
<p>Can be written like this:</p>
<div class="CodeRay">
<div class="code">
<pre><span class="line-numbers"><a href="#n1" name="n1">1</a></span>?[
<span class="line-numbers"><a href="#n2" name="n2">2</a></span> not/output?[pdf]|
<span class="line-numbers"><a href="#n3" name="n3">3</a></span> ...
<span class="line-numbers"><a href="#n4" name="n4">4</a></span>]</pre>
</div>
</div>
<p>In this case, the <a href="/glyph/book/macros/macros_core.html#m_not"><code>not</code></a> macro was composed with
the <a href="/glyph/book/macros/macros_core.html#m_output_"><code>output?</code></a> macro, thus removing one level of
nesting.</p>
<p>Composition can be useful to simplify complex Glyph macro constructs, but also for <em>macro dispatching</em>.
Currently, Glyph supports two <em>dispatchers</em>:</p>
<ul>
<li>The <a href="/glyph/book/macros/macros_core.html#m_s"><code>s</code></a> macro, used to call almost any method of
the Ruby String class.</li>
<li>The <a href="/glyph/book/macros/macros_core.html#m_xml"><code>xml</code></a> macro, used to render raw <span
class="caps">XML</span> tags.</li>
</ul>
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