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<?xml version="1.0" encoding="utf-8"?>
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		<title>Glyph - A quick look at Glyph's internals</title>
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						<h2>A quick look at Glyph's internals</h2>
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							<div class="navigation"><a href="/glyph/book/stats/links.html">Link Statistics &larr;</a><a href="/glyph/book/index.html">Contents</a><a href="/glyph/book/extending/macro_def.html">&rarr; Defining Custom Macros</a></div>
								<p>If you plan on extending Glyph, knowing how it works inside helps. It is not mandatory by any means, but it definitely helps, especially when creating complex macros.</p>
	<p>What happens behind the scenes when you call <code>glyph compile</code>? Glyph's code is parsed, analyzed and then translated into text, and here's how:</p>
	<div class="figure"><img alt="-" src="/glyph/book/images/glyph/document_generation.png" />
					<div class="caption">A sequence diagram for document generation</div></div>
	<p>From the diagram, it is possible to divide the document generation process into three phases:</p>
<ul>
	<li>The <em>Parsing Phase</em> starts when a chunk of Glyph code is passed (by the <code>generate:document</code> Rake task, for example) to a <a href="http://yardoc.org/docs/h3rald-glyph/Glyph/Interpreter"><code>Glyph::Interpreter</code></a>. The interpreter initializes a <a href="http://yardoc.org/docs/h3rald-glyph/Glyph/Parser"><code>Glyph::Parser</code></a> that parses the code and returns an <em>Abstract Syntax Tree</em> (<span class="caps">AST</span>) of <a href="http://yardoc.org/docs/h3rald-glyph/Glyph/SyntaxNode"><code>Glyph::SyntaxNode</code></a> objects.</li>
	<li>The <em>Analysis Phase</em> (Processing) starts when the interpreter method calls the <code>analyze</code> method, instantiating a new <a href="http://yardoc.org/docs/h3rald-glyph/Glyph/Document"><code>Glyph::Document</code></a>. The <code>Glyph::Document</code> object evaluates the <span class="caps">AST</span> expanding all macro nodesth (that&#8217;s when macros are executed) and generates string.</li>
	<li>The <em>Finalization Phase</em> (Post-Processing) starts when the interpreter calls the <code>finalyze</code> method, causing the <code>Glyph::Document</code> object to perform a series of finalizations on the string obtained after analysis, i.e. it replaces escape sequences and placeholders.</li>
</ul>
	<div class="section">
<h4 id="h_73">Example: A short note</h4>
<p>As an example, consider the following Glyph code:</p>
		<pre class="lazy"><span class="line-numbers">   1 </span> fmi[something|#test]
<span class="line-numbers">   2 </span> ...
<span class="line-numbers">   3 </span> section[
<span class="line-numbers">   4 </span>   @title[Test Section]
<span class="line-numbers">   5 </span>   @id[test]
<span class="line-numbers">   6 </span> ...
<span class="line-numbers">   7 </span> ]
</pre>
		<p>This simple snippet uses the <a href="/glyph/book/macros/macros_inline.html#m_fmi"><code>fmi</code></a> macro to link to a section later on in the document. When parsed, the produced AST is the following:</p>
		<pre class="lazy"><span class="line-numbers">   1 </span> {<span class="Constant"><span class="Constant">:</span>name</span>=&gt;<span class="Constant"><span class="Constant">:&quot;</span>--<span class="Constant">&quot;</span></span>}
<span class="line-numbers">   2 </span>   {<span class="Constant"><span class="Constant">:</span>name</span>=&gt;<span class="Constant"><span class="Constant">:</span>fmi</span>, <span class="Constant"><span class="Constant">:</span>escape</span>=&gt;<span class="Constant">false</span>}
<span class="line-numbers">   3 </span>     {<span class="Constant"><span class="Constant">:</span>name</span>=&gt;<span class="Constant"><span class="Constant">:&quot;</span>0<span class="Constant">&quot;</span></span>}
<span class="line-numbers">   4 </span>       {<span class="Constant"><span class="Constant">:</span>value</span>=&gt;<span class="String"><span class="String">&quot;</span>something<span class="String">&quot;</span></span>}
<span class="line-numbers">   5 </span>     {<span class="Constant"><span class="Constant">:</span>name</span>=&gt;<span class="Constant"><span class="Constant">:&quot;</span>1<span class="Constant">&quot;</span></span>}
<span class="line-numbers">   6 </span>       {<span class="Constant"><span class="Constant">:</span>value</span>=&gt;<span class="String"><span class="String">&quot;</span>#test<span class="String">&quot;</span></span>}
<span class="line-numbers">   7 </span>   {<span class="Constant"><span class="Constant">:</span>value</span>=&gt;<span class="String"><span class="String">&quot;</span><span class="Constant">\n</span><span class="String">&quot;</span></span>}
<span class="line-numbers">   8 </span>   {<span class="Constant"><span class="Constant">:</span>value</span>=&gt;<span class="String"><span class="String">&quot;</span><span class="Constant">\</span>[<span class="String">&quot;</span></span>, <span class="Constant"><span class="Constant">:</span>escaped</span>=&gt;<span class="Constant">true</span>}
<span class="line-numbers">   9 </span>   {<span class="Constant"><span class="Constant">:</span>value</span>=&gt;<span class="String"><span class="String">&quot;</span>...<span class="String">&quot;</span></span>}
<span class="line-numbers">  10 </span>   {<span class="Constant"><span class="Constant">:</span>value</span>=&gt;<span class="String"><span class="String">&quot;</span><span class="Constant">\</span>]<span class="String">&quot;</span></span>, <span class="Constant"><span class="Constant">:</span>escaped</span>=&gt;<span class="Constant">true</span>}
<span class="line-numbers">  11 </span>   {<span class="Constant"><span class="Constant">:</span>value</span>=&gt;<span class="String"><span class="String">&quot;</span><span class="Constant">\n</span><span class="String">&quot;</span></span>}
<span class="line-numbers">  12 </span>   {<span class="Constant"><span class="Constant">:</span>name</span>=&gt;<span class="Constant"><span class="Constant">:</span>section</span>, <span class="Constant"><span class="Constant">:</span>escape</span>=&gt;<span class="Constant">false</span>}
<span class="line-numbers">  13 </span>     {<span class="Constant"><span class="Constant">:</span>name</span>=&gt;<span class="Constant"><span class="Constant">:&quot;</span>0<span class="Constant">&quot;</span></span>}
<span class="line-numbers">  14 </span>       {<span class="Constant"><span class="Constant">:</span>value</span>=&gt;<span class="String"><span class="String">&quot;</span><span class="Constant">\n</span><span class="Constant">\t</span><span class="String">&quot;</span></span>}
<span class="line-numbers">  15 </span>       {<span class="Constant"><span class="Constant">:</span>value</span>=&gt;<span class="String"><span class="String">&quot;</span><span class="Constant">\n</span><span class="Constant">\t</span><span class="String">&quot;</span></span>}
<span class="line-numbers">  16 </span>       {<span class="Constant"><span class="Constant">:</span>value</span>=&gt;<span class="String"><span class="String">&quot;</span><span class="Constant">\n</span><span class="String">&quot;</span></span>}
<span class="line-numbers">  17 </span>       {<span class="Constant"><span class="Constant">:</span>value</span>=&gt;<span class="String"><span class="String">&quot;</span><span class="Constant">\</span>[<span class="String">&quot;</span></span>, <span class="Constant"><span class="Constant">:</span>escaped</span>=&gt;<span class="Constant">true</span>}
<span class="line-numbers">  18 </span>       {<span class="Constant"><span class="Constant">:</span>value</span>=&gt;<span class="String"><span class="String">&quot;</span>...<span class="String">&quot;</span></span>}
<span class="line-numbers">  19 </span>       {<span class="Constant"><span class="Constant">:</span>value</span>=&gt;<span class="String"><span class="String">&quot;</span><span class="Constant">\</span>]<span class="String">&quot;</span></span>, <span class="Constant"><span class="Constant">:</span>escaped</span>=&gt;<span class="Constant">true</span>}
<span class="line-numbers">  20 </span>       {<span class="Constant"><span class="Constant">:</span>value</span>=&gt;<span class="String"><span class="String">&quot;</span><span class="Constant">\n</span><span class="String">&quot;</span></span>}
<span class="line-numbers">  21 </span>     {<span class="Constant"><span class="Constant">:</span>name</span>=&gt;<span class="Constant"><span class="Constant">:</span>title</span>, <span class="Constant"><span class="Constant">:</span>escape</span>=&gt;<span class="Constant">false</span>}
<span class="line-numbers">  22 </span>       {<span class="Constant"><span class="Constant">:</span>value</span>=&gt;<span class="String"><span class="String">&quot;</span>Test Section<span class="String">&quot;</span></span>}
<span class="line-numbers">  23 </span>     {<span class="Constant"><span class="Constant">:</span>name</span>=&gt;<span class="Constant"><span class="Constant">:</span>id</span>, <span class="Constant"><span class="Constant">:</span>escape</span>=&gt;<span class="Constant">false</span>}
<span class="line-numbers">  24 </span>       {<span class="Constant"><span class="Constant">:</span>value</span>=&gt;<span class="String"><span class="String">&quot;</span>test<span class="String">&quot;</span></span>}
</pre>
		<p>This output is produced by calling the <code>inspect</code> method on the AST. Each <a href="http://yardoc.org/docs/h3rald-glyph/Glyph/SyntaxNode"><code>Glyph::SyntaxNode</code></a> object in the tree is basically an ordinary Glyph Hash with a parent and 0 or more chidren, so the code snippets above shows how the syntax nodes are nested.</p>
		<p>The AST contains information about macro, parameter and attribute names, and escaping, and raw text values (the nodes without a <code>:name</code> key), but nothing more.</p>
		<p>When the AST is analyzed, the resulting textual output is the following:</p>
		<pre class="lazy"><span class="line-numbers">   1 </span> <span class="MetaTag"><span class="MetaTag">&lt;</span><span class="MetaTag">span</span> <span class="MetaTag">class</span>=<span class="String"><span class="String">&quot;</span>fmi<span class="String">&quot;</span></span><span class="MetaTag">&gt;</span></span>for more information on something, see ‡‡‡‡‡PLACEHOLDER ¤ 1‡‡‡‡‡
<span class="line-numbers">   2 </span> <span class="MetaTag"><span class="MetaTag">&lt;/</span><span class="MetaTag">span</span><span class="MetaTag">&gt;</span></span>
<span class="line-numbers">   3 </span> [...]
<span class="line-numbers">   4 </span> <span class="MetaTag"><span class="MetaTag">&lt;</span><span class="MetaTag">div</span> <span class="MetaTag">class</span>=<span class="String"><span class="String">&quot;</span>section<span class="String">&quot;</span></span><span class="MetaTag">&gt;</span></span>
<span class="line-numbers">   5 </span> <span class="MetaTag"><span class="MetaTag">&lt;</span><span class="MetaTag">h2</span> <span class="MetaTag"><span class="MetaTag">id</span><span class="MetaTag">=</span><span class="String"><span class="String">&quot;</span><span class="String">test</span><span class="String">&quot;</span></span></span><span class="MetaTag">&gt;</span></span>Test Section<span class="MetaTag"><span class="MetaTag">&lt;/</span><span class="MetaTag">h2</span><span class="MetaTag">&gt;</span></span>
<span class="line-numbers">   6 </span> [...]
<span class="line-numbers">   7 </span> 
<span class="line-numbers">   8 </span> <span class="MetaTag"><span class="MetaTag">&lt;/</span><span class="MetaTag">div</span><span class="MetaTag">&gt;</span></span>
</pre>
		<p>This looks almost perfect, except that:</p>
		<ul><li>There's a nasty placeholder instead of a link: this is due to the fact that when the link is processed, there is no <code>#text</code> anchor in the document, but there may be one afterwards (and there will be).</li>
			<li>There are some escaped brackets.</li></ul>
		<p>Finally, when the document is finalized, placeholders and escape sequences are removed and the final result is the following:</p>
		<pre class="lazy"><span class="line-numbers">   1 </span> <span class="MetaTag"><span class="MetaTag">&lt;</span><span class="MetaTag">span</span> <span class="MetaTag">class</span>=<span class="String"><span class="String">&quot;</span>fmi<span class="String">&quot;</span></span><span class="MetaTag">&gt;</span></span>for more information on something, 
<span class="line-numbers">   2 </span>   see <span class="MetaTag"><span class="MetaTag">&lt;</span><span class="MetaTag">a</span> <span class="MetaTag">href</span>=<span class="String"><span class="String">&quot;</span>#test<span class="String">&quot;</span></span><span class="MetaTag">&gt;</span></span>Test Section<span class="MetaTag"><span class="MetaTag">&lt;/</span><span class="MetaTag">a</span><span class="MetaTag">&gt;</span></span><span class="MetaTag"><span class="MetaTag">&lt;/</span><span class="MetaTag">span</span><span class="MetaTag">&gt;</span></span>
<span class="line-numbers">   3 </span> [...]
<span class="line-numbers">   4 </span> <span class="MetaTag"><span class="MetaTag">&lt;</span><span class="MetaTag">div</span> <span class="MetaTag">class</span>=<span class="String"><span class="String">&quot;</span>section<span class="String">&quot;</span></span><span class="MetaTag">&gt;</span></span>
<span class="line-numbers">   5 </span> <span class="MetaTag"><span class="MetaTag">&lt;</span><span class="MetaTag">h2</span> <span class="MetaTag"><span class="MetaTag">id</span><span class="MetaTag">=</span><span class="String"><span class="String">&quot;</span><span class="String">test</span><span class="String">&quot;</span></span></span><span class="MetaTag">&gt;</span></span>Test Section<span class="MetaTag"><span class="MetaTag">&lt;/</span><span class="MetaTag">h2</span><span class="MetaTag">&gt;</span></span>
<span class="line-numbers">   6 </span> [...]
<span class="line-numbers">   7 </span> 
<span class="line-numbers">   8 </span> <span class="MetaTag"><span class="MetaTag">&lt;/</span><span class="MetaTag">div</span><span class="MetaTag">&gt;</span></span>
</pre>

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