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<h1>A quick look at Glyph's internals</h1>
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<section id="body-text" class="hyphenate">
<nav><a href="/glyph/book/stats/links.html">Link Statistics ←</a><a href="/glyph/book/index.html">Contents</a><a href="/glyph/book/extending/macro_def.html">→ Defining Custom Macros</a></nav>
<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>
<figure><img alt="-" src="images/glyph/document_generation.png" />
<figcaption>A sequence diagram for document generation</figcaption></figure>
<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’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>
<section class="section">
<header><h1 id="h_73">Example: A short note</h1></header>
<p>As an example, consider the following Glyph code:</p>
<div class="CodeRay">
<div class="code"><pre><span class="no">1</span> fmi[something|#test]
<span class="no">2</span> ...
<span class="no">3</span> section[
<span class="no">4</span> @title[Test Section]
<span class="no">5</span> @id[test]
<span class="no">6</span> ...
<span class="no">7</span> ]</pre></div>
</div>
<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>
<div class="CodeRay">
<div class="code"><pre><span class="no"> 1</span> {<span class="sy">:name</span>=><span class="sy"><span class="sy">:</span><span class="dl">"</span><span class="k">--</span><span class="dl">"</span></span>}
<span class="no"> 2</span> {<span class="sy">:name</span>=><span class="sy">:fmi</span>, <span class="sy">:escape</span>=><span class="pc">false</span>}
<span class="no"> 3</span> {<span class="sy">:name</span>=><span class="sy"><span class="sy">:</span><span class="dl">"</span><span class="k">0</span><span class="dl">"</span></span>}
<span class="no"> 4</span> {<span class="sy">:value</span>=><span class="s"><span class="dl">"</span><span class="k">something</span><span class="dl">"</span></span>}
<span class="no"> 5</span> {<span class="sy">:name</span>=><span class="sy"><span class="sy">:</span><span class="dl">"</span><span class="k">1</span><span class="dl">"</span></span>}
<span class="no"> 6</span> {<span class="sy">:value</span>=><span class="s"><span class="dl">"</span><span class="k">#test</span><span class="dl">"</span></span>}
<span class="no"> 7</span> {<span class="sy">:value</span>=><span class="s"><span class="dl">"</span><span class="ch">\n</span><span class="dl">"</span></span>}
<span class="no"> 8</span> {<span class="sy">:value</span>=><span class="s"><span class="dl">"</span><span class="ch">\</span><span class="k">[</span><span class="dl">"</span></span>, <span class="sy">:escaped</span>=><span class="pc">true</span>}
<span class="no"> 9</span> {<span class="sy">:value</span>=><span class="s"><span class="dl">"</span><span class="k">...</span><span class="dl">"</span></span>}
<span class="no"><strong>10</strong></span> {<span class="sy">:value</span>=><span class="s"><span class="dl">"</span><span class="ch">\</span><span class="k">]</span><span class="dl">"</span></span>, <span class="sy">:escaped</span>=><span class="pc">true</span>}
<span class="no">11</span> {<span class="sy">:value</span>=><span class="s"><span class="dl">"</span><span class="ch">\n</span><span class="dl">"</span></span>}
<span class="no">12</span> {<span class="sy">:name</span>=><span class="sy">:section</span>, <span class="sy">:escape</span>=><span class="pc">false</span>}
<span class="no">13</span> {<span class="sy">:name</span>=><span class="sy"><span class="sy">:</span><span class="dl">"</span><span class="k">0</span><span class="dl">"</span></span>}
<span class="no">14</span> {<span class="sy">:value</span>=><span class="s"><span class="dl">"</span><span class="ch">\n</span><span class="ch">\t</span><span class="dl">"</span></span>}
<span class="no">15</span> {<span class="sy">:value</span>=><span class="s"><span class="dl">"</span><span class="ch">\n</span><span class="ch">\t</span><span class="dl">"</span></span>}
<span class="no">16</span> {<span class="sy">:value</span>=><span class="s"><span class="dl">"</span><span class="ch">\n</span><span class="dl">"</span></span>}
<span class="no">17</span> {<span class="sy">:value</span>=><span class="s"><span class="dl">"</span><span class="ch">\</span><span class="k">[</span><span class="dl">"</span></span>, <span class="sy">:escaped</span>=><span class="pc">true</span>}
<span class="no">18</span> {<span class="sy">:value</span>=><span class="s"><span class="dl">"</span><span class="k">...</span><span class="dl">"</span></span>}
<span class="no">19</span> {<span class="sy">:value</span>=><span class="s"><span class="dl">"</span><span class="ch">\</span><span class="k">]</span><span class="dl">"</span></span>, <span class="sy">:escaped</span>=><span class="pc">true</span>}
<span class="no"><strong>20</strong></span> {<span class="sy">:value</span>=><span class="s"><span class="dl">"</span><span class="ch">\n</span><span class="dl">"</span></span>}
<span class="no">21</span> {<span class="sy">:name</span>=><span class="sy">:title</span>, <span class="sy">:escape</span>=><span class="pc">false</span>}
<span class="no">22</span> {<span class="sy">:value</span>=><span class="s"><span class="dl">"</span><span class="k">Test Section</span><span class="dl">"</span></span>}
<span class="no">23</span> {<span class="sy">:name</span>=><span class="sy">:id</span>, <span class="sy">:escape</span>=><span class="pc">false</span>}
<span class="no">24</span> {<span class="sy">:value</span>=><span class="s"><span class="dl">"</span><span class="k">test</span><span class="dl">"</span></span>}</pre></div>
</div>
<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>
<div class="CodeRay">
<div class="code"><pre><span class="no">1</span> <span class="ta"><span</span> <span class="an">class</span>=<span class="s"><span class="dl">"</span><span class="k">fmi</span><span class="dl">"</span></span><span class="ta">></span>for more information on something, see ‡‡‡‡‡PLACEHOLDER ¤ 1‡‡‡‡‡
<span class="no">2</span> <span class="ta"></span></span>
<span class="no">3</span> \.[...\.]
<span class="no">4</span> <span class="ta"><div</span> <span class="an">class</span>=<span class="s"><span class="dl">"</span><span class="k">section</span><span class="dl">"</span></span><span class="ta">></span>
<span class="no">5</span> <span class="ta"><h2</span> <span class="an">id</span>=<span class="s"><span class="dl">"</span><span class="k">test</span><span class="dl">"</span></span><span class="ta">></span>Test Section<span class="ta"></h2></span>
<span class="no">6</span> \.[...\.]
<span class="no">7</span>
<span class="no">8</span> <span class="ta"></div></span></pre></div>
</div>
<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>
<div class="CodeRay">
<div class="code"><pre><span class="no">1</span> <span class="ta"><span</span> <span class="an">class</span>=<span class="s"><span class="dl">"</span><span class="k">fmi</span><span class="dl">"</span></span><span class="ta">></span>for more information on something,
<span class="no">2</span> see <span class="ta"><a</span> <span class="an">href</span>=<span class="s"><span class="dl">"</span><span class="k">#test</span><span class="dl">"</span></span><span class="ta">></span>Test Section<span class="ta"></a></span><span class="ta"></span></span>
<span class="no">3</span> [...]
<span class="no">4</span> <span class="ta"><div</span> <span class="an">class</span>=<span class="s"><span class="dl">"</span><span class="k">section</span><span class="dl">"</span></span><span class="ta">></span>
<span class="no">5</span> <span class="ta"><h2</span> <span class="an">id</span>=<span class="s"><span class="dl">"</span><span class="k">test</span><span class="dl">"</span></span><span class="ta">></span>Test Section<span class="ta"></h2></span>
<span class="no">6</span> [...]
<span class="no">7</span>
<span class="no">8</span> <span class="ta"></div></span></pre></div>
</div>
</section>
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