content/glyph/book/extending/internals.html
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<h2>A quick look at Glyph's internals</h2>
<hr />
<div id="content-body">
<div class="navigation"><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></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’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>=><span class="Constant"><span class="Constant">:"</span>--<span class="Constant">"</span></span>}
<span class="line-numbers"> 2 </span> {<span class="Constant"><span class="Constant">:</span>name</span>=><span class="Constant"><span class="Constant">:</span>fmi</span>, <span class="Constant"><span class="Constant">:</span>escape</span>=><span class="Constant">false</span>}
<span class="line-numbers"> 3 </span> {<span class="Constant"><span class="Constant">:</span>name</span>=><span class="Constant"><span class="Constant">:"</span>0<span class="Constant">"</span></span>}
<span class="line-numbers"> 4 </span> {<span class="Constant"><span class="Constant">:</span>value</span>=><span class="String"><span class="String">"</span>something<span class="String">"</span></span>}
<span class="line-numbers"> 5 </span> {<span class="Constant"><span class="Constant">:</span>name</span>=><span class="Constant"><span class="Constant">:"</span>1<span class="Constant">"</span></span>}
<span class="line-numbers"> 6 </span> {<span class="Constant"><span class="Constant">:</span>value</span>=><span class="String"><span class="String">"</span>#test<span class="String">"</span></span>}
<span class="line-numbers"> 7 </span> {<span class="Constant"><span class="Constant">:</span>value</span>=><span class="String"><span class="String">"</span><span class="Constant">\n</span><span class="String">"</span></span>}
<span class="line-numbers"> 8 </span> {<span class="Constant"><span class="Constant">:</span>value</span>=><span class="String"><span class="String">"</span><span class="Constant">\</span>[<span class="String">"</span></span>, <span class="Constant"><span class="Constant">:</span>escaped</span>=><span class="Constant">true</span>}
<span class="line-numbers"> 9 </span> {<span class="Constant"><span class="Constant">:</span>value</span>=><span class="String"><span class="String">"</span>...<span class="String">"</span></span>}
<span class="line-numbers"> 10 </span> {<span class="Constant"><span class="Constant">:</span>value</span>=><span class="String"><span class="String">"</span><span class="Constant">\</span>]<span class="String">"</span></span>, <span class="Constant"><span class="Constant">:</span>escaped</span>=><span class="Constant">true</span>}
<span class="line-numbers"> 11 </span> {<span class="Constant"><span class="Constant">:</span>value</span>=><span class="String"><span class="String">"</span><span class="Constant">\n</span><span class="String">"</span></span>}
<span class="line-numbers"> 12 </span> {<span class="Constant"><span class="Constant">:</span>name</span>=><span class="Constant"><span class="Constant">:</span>section</span>, <span class="Constant"><span class="Constant">:</span>escape</span>=><span class="Constant">false</span>}
<span class="line-numbers"> 13 </span> {<span class="Constant"><span class="Constant">:</span>name</span>=><span class="Constant"><span class="Constant">:"</span>0<span class="Constant">"</span></span>}
<span class="line-numbers"> 14 </span> {<span class="Constant"><span class="Constant">:</span>value</span>=><span class="String"><span class="String">"</span><span class="Constant">\n</span><span class="Constant">\t</span><span class="String">"</span></span>}
<span class="line-numbers"> 15 </span> {<span class="Constant"><span class="Constant">:</span>value</span>=><span class="String"><span class="String">"</span><span class="Constant">\n</span><span class="Constant">\t</span><span class="String">"</span></span>}
<span class="line-numbers"> 16 </span> {<span class="Constant"><span class="Constant">:</span>value</span>=><span class="String"><span class="String">"</span><span class="Constant">\n</span><span class="String">"</span></span>}
<span class="line-numbers"> 17 </span> {<span class="Constant"><span class="Constant">:</span>value</span>=><span class="String"><span class="String">"</span><span class="Constant">\</span>[<span class="String">"</span></span>, <span class="Constant"><span class="Constant">:</span>escaped</span>=><span class="Constant">true</span>}
<span class="line-numbers"> 18 </span> {<span class="Constant"><span class="Constant">:</span>value</span>=><span class="String"><span class="String">"</span>...<span class="String">"</span></span>}
<span class="line-numbers"> 19 </span> {<span class="Constant"><span class="Constant">:</span>value</span>=><span class="String"><span class="String">"</span><span class="Constant">\</span>]<span class="String">"</span></span>, <span class="Constant"><span class="Constant">:</span>escaped</span>=><span class="Constant">true</span>}
<span class="line-numbers"> 20 </span> {<span class="Constant"><span class="Constant">:</span>value</span>=><span class="String"><span class="String">"</span><span class="Constant">\n</span><span class="String">"</span></span>}
<span class="line-numbers"> 21 </span> {<span class="Constant"><span class="Constant">:</span>name</span>=><span class="Constant"><span class="Constant">:</span>title</span>, <span class="Constant"><span class="Constant">:</span>escape</span>=><span class="Constant">false</span>}
<span class="line-numbers"> 22 </span> {<span class="Constant"><span class="Constant">:</span>value</span>=><span class="String"><span class="String">"</span>Test Section<span class="String">"</span></span>}
<span class="line-numbers"> 23 </span> {<span class="Constant"><span class="Constant">:</span>name</span>=><span class="Constant"><span class="Constant">:</span>id</span>, <span class="Constant"><span class="Constant">:</span>escape</span>=><span class="Constant">false</span>}
<span class="line-numbers"> 24 </span> {<span class="Constant"><span class="Constant">:</span>value</span>=><span class="String"><span class="String">"</span>test<span class="String">"</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"><</span><span class="MetaTag">span</span> <span class="MetaTag">class</span>=<span class="String"><span class="String">"</span>fmi<span class="String">"</span></span><span class="MetaTag">></span></span>for more information on something, see ‡‡‡‡‡PLACEHOLDER ¤ 1‡‡‡‡‡
<span class="line-numbers"> 2 </span> <span class="MetaTag"><span class="MetaTag"></</span><span class="MetaTag">span</span><span class="MetaTag">></span></span>
<span class="line-numbers"> 3 </span> [...]
<span class="line-numbers"> 4 </span> <span class="MetaTag"><span class="MetaTag"><</span><span class="MetaTag">div</span> <span class="MetaTag">class</span>=<span class="String"><span class="String">"</span>section<span class="String">"</span></span><span class="MetaTag">></span></span>
<span class="line-numbers"> 5 </span> <span class="MetaTag"><span class="MetaTag"><</span><span class="MetaTag">h2</span> <span class="MetaTag"><span class="MetaTag">id</span><span class="MetaTag">=</span><span class="String"><span class="String">"</span><span class="String">test</span><span class="String">"</span></span></span><span class="MetaTag">></span></span>Test Section<span class="MetaTag"><span class="MetaTag"></</span><span class="MetaTag">h2</span><span class="MetaTag">></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"></</span><span class="MetaTag">div</span><span class="MetaTag">></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"><</span><span class="MetaTag">span</span> <span class="MetaTag">class</span>=<span class="String"><span class="String">"</span>fmi<span class="String">"</span></span><span class="MetaTag">></span></span>for more information on something,
<span class="line-numbers"> 2 </span> see <span class="MetaTag"><span class="MetaTag"><</span><span class="MetaTag">a</span> <span class="MetaTag">href</span>=<span class="String"><span class="String">"</span>#test<span class="String">"</span></span><span class="MetaTag">></span></span>Test Section<span class="MetaTag"><span class="MetaTag"></</span><span class="MetaTag">a</span><span class="MetaTag">></span></span><span class="MetaTag"><span class="MetaTag"></</span><span class="MetaTag">span</span><span class="MetaTag">></span></span>
<span class="line-numbers"> 3 </span> [...]
<span class="line-numbers"> 4 </span> <span class="MetaTag"><span class="MetaTag"><</span><span class="MetaTag">div</span> <span class="MetaTag">class</span>=<span class="String"><span class="String">"</span>section<span class="String">"</span></span><span class="MetaTag">></span></span>
<span class="line-numbers"> 5 </span> <span class="MetaTag"><span class="MetaTag"><</span><span class="MetaTag">h2</span> <span class="MetaTag"><span class="MetaTag">id</span><span class="MetaTag">=</span><span class="String"><span class="String">"</span><span class="String">test</span><span class="String">"</span></span></span><span class="MetaTag">></span></span>Test Section<span class="MetaTag"><span class="MetaTag"></</span><span class="MetaTag">h2</span><span class="MetaTag">></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"></</span><span class="MetaTag">div</span><span class="MetaTag">></span></span>
</pre>
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