content/glyph/book/extending/interpreting.html
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<h1>Interpreting Glyph Code</h1>
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<nav><a href="/glyph/book/extending/validators.html">Using Validators ←</a><a href="/glyph/book/index.html">Contents</a><a href="/glyph/book/extending/layouts.html">→ Layouts</a></nav>
<p>What if you need to evaluate some Glyph code <em>within</em> a macro? Say for example you want to transform a parameter in a link, and you want to make sure that link gets validated exactly like the others, in this case, you can use the <code>interpret</code> method, as follows:</p>
<div class="CodeRay">
<div class="code"><pre><span class="no">1</span> macro <span class="sy">:fmi</span> <span class="r">do</span>
<span class="no">2</span> topic, href = <span class="iv">@params</span>
<span class="no">3</span> link = placeholder <span class="r">do</span> |document|
<span class="no">4</span> interpret <span class="s"><span class="dl">"</span><span class="k">link[</span><span class="il"><span class="idl">#{</span>href<span class="idl">}</span></span><span class="k">]</span><span class="dl">"</span></span>
<span class="no">5</span> <span class="r">end</span>
<span class="no">6</span> <span class="s"><span class="dl">%{</span><span class="k"><span class="fmi">for more information on </span><span class="il"><span class="idl">#{</span>topic<span class="idl">}</span></span><span class="k">, see </span><span class="il"><span class="idl">#{</span>link<span class="idl">}</span></span><span class="k"></span></span><span class="dl">}</span></span>
<span class="no">7</span> <span class="r">end</span></pre></div>
</div>
<p>When the <code>interpret</code> method is called, the following happens:</p>
<ol>
<li>A new Glyph document is created from the <code>String</code> passed to the method.</li>
<li>The bookmarks, headers and placeholders are passed from the main document to the new one. Because they are stored in arrays and hashes, they are passed by reference, so for example any new bookmark stored in the new document will also become available in the main document.</li>
<li>Any macro included in the <code>String</code> is evaluated, and the resulting text is returned by the method. Note that this new document does not get finalized: in other words, placeholders will be left as they are, and they’ll eventually be replaced when <em>the main document</em> is finalized.</li>
</ol>
<section class="section">
<header><h1 id="rewriting">Rewriting</h1></header>
<p>While the <code>interpret</code> method is useful to evaluate Glyph code in a macro while performing other actions (storing a bookmark, checking for the presence of an anchor, etc.), in some cases it may not be necessary. If you simply want your macro to be converted into existing Glyph macro without performing any action excepting parameter substitution, you can just use the <a href="/glyph/book/macros/macros_core.html#m_rewrite_"><code>rewrite:</code></a> macro within youy Glyph document</p>
<p>Consider the following macro definition:</p>
<div class="CodeRay">
<div class="code"><pre><span class="no">1</span> macro <span class="sy">:issue</span> <span class="r">do</span>
<span class="no">2</span> interpret <span class="s"><span class="dl">%{</span><span class="k">
<span class="no">3</span> tr[
<span class="no">4</span> td[.=>[http://github.com/h3rald/glyph/issues/closed#issue/</span><span class="il"><span class="idl">#{</span>param[<span class="i">0</span>]<span class="idl">}</span></span><span class="k">|#</span><span class="il"><span class="idl">#{</span>param(<span class="i">0</span>)<span class="idl">}</span></span><span class="k">]]
<span class="no">5</span> td[txt[</span><span class="il"><span class="idl">#{</span>param(<span class="i">1</span>)<span class="idl">}</span></span><span class="k">]]
<span class="no">6</span> ]
<span class="no">7</span> </span><span class="dl">}</span></span>
<span class="no">8</span> <span class="r">end</span></pre></div>
</div>
<p>The <code>issue</code> macro is only rewriting existing Glyph code around the two parameters provided. In this case, it is possible to do exactly the same thing using the <a href="/glyph/book/macros/macros_core.html#m_rewrite_"><code>rewrite:</code></a> macro:</p>
<div class="CodeRay">
<div class="code"><pre><span class="no">1</span> rewrite:[issue|
<span class="no">2</span> tr[
<span class="no">3</span> td[.=<span class="er">></span>[http://github.com/h3rald/glyph/issues/closed#issue/{{0}}|#{{0}}]]
<span class="no">4</span> td[txt[{{1}}]]
<span class="no">5</span> ]
<span class="no">6</span> ]</pre></div>
</div>
<p>Within the <a href="/glyph/book/macros/macros_core.html#m_rewrite_"><code>rewrite:</code></a> macro, it is possible to use a special syntax to call the <code>raw_attr</code> or <code>raw_param</code> methods: <br />
<code>{{</code><em>parameter_number</em> or <em>attribute_name</em><code>}}</code></p>
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