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<h2>Parameters and Attributes</h2>
<hr />
<div id="content-body">
<div class="navigation"><a href="/glyph/book/extending/macro_def.html">Defining Custom Macros ←</a><a href="/glyph/book/index.html">Contents</a><a href="/glyph/book/extending/bookmarks_headers.html">→ Bookmarks and Headers</a></div>
<p>Perhaps the most common things to do in a macro definition is accessing parameters and attributes. When doing so, it is important to consider whether we want to retrieve the <em>raw value</em> of and attribute or parameter or its <em>expanded value</em>. The difference between the two will become clearer in the following sections and also in the <a href="/glyph/book/extending/interpreting.html#interpreting">Interpreting Glyph Code</a> section.</p>
<div class="section">
<h5 id="expanded_values">Accessing Expanded Values</h5>
<p>Normally, you just want to get the value of an attribute or parameter and use it in the macro. This means, in other words, its <em>expanded</em> value, i.e. the value resulting from the expansion of the macros (if any) within the attribute or parameter.</p>
<p>To access expanded values, use the following methods:</p>
<ul>
<li><code>parameter</code> (or <code>param</code>): Returns the expanded value of the parameter specified by number. Other parameters are not expanded.</li>
<li><code>value</code>: Returns the expanded value of the first parameter (i.e. like <code>parameter(0)</code>).</li>
<li><code>attribute</code> (or <code>attr</code>): Returns the expanded value of the attribute specified by name. Other attributes are not expanded.</li>
<li><code>parameters</code> (or <code>params</code>): Returns an array of expanded parameters.</li>
<li><code>attributes</code> (or <code>attrs</code>): Returns a hash of expanded attributes.</li>
</ul>
</div>
<div class="section">
<h5 id="h_77">Accessing Raw Values</h5>
<p>While accessing expanded values is simple and immediate, in some cases it may not produce the desired results. Consider the following macro definition:</p>
<pre class="lazy"><span class="line-numbers"> 1 </span> macro <span class="Constant"><span class="Constant">:</span>nest_section</span> <span class="Keyword">do</span>
<span class="line-numbers"> 2 </span> interpret <span class="String"><span class="String">%{</span>section[</span>
<span class="line-numbers"> 3 </span> <span class="String"> @title[A]</span>
<span class="line-numbers"> 4 </span> <span class="String"> section[</span>
<span class="line-numbers"> 5 </span> <span class="String"> @title[B]</span>
<span class="line-numbers"> 6 </span> <span class="String"> <span class="String"><span class="String">#{</span>value<span class="String">}</span></span></span>
<span class="line-numbers"> 7 </span> <span class="String"> ]</span>
<span class="line-numbers"> 8 </span> <span class="String"> ]<span class="String">}</span></span>
<span class="line-numbers"> 9 </span> <span class="Keyword">end</span>
</pre>
<p>And suppose to use it as follows:</p>
<pre class="lazy"><span class="line-numbers"> 1 </span> nest_section[
<span class="line-numbers"> 2 </span> section[
<span class="line-numbers"> 3 </span> <span class="Variable"><span class="Variable">@</span>title</span>[<span class="Variable">Inner</span> <span class="Variable">Section</span>]
<span class="line-numbers"> 4 </span> ...
<span class="line-numbers"> 5 </span> ]
<span class="line-numbers"> 6 </span> ]
</pre>
<p>It produces the following HTML code:</p>
<pre class="lazy"><span class="line-numbers"> 1 </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"> 2 </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">h_2</span><span class="String">"</span></span></span><span class="MetaTag">></span></span>A<span class="MetaTag"><span class="MetaTag"></</span><span class="MetaTag">h2</span><span class="MetaTag">></span></span>
<span class="line-numbers"> 3 </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"> 4 </span> <span class="MetaTag"><span class="MetaTag"><</span><span class="MetaTag">h3</span> <span class="MetaTag"><span class="MetaTag">id</span><span class="MetaTag">=</span><span class="String"><span class="String">"</span><span class="String">h_3</span><span class="String">"</span></span></span><span class="MetaTag">></span></span>B<span class="MetaTag"><span class="MetaTag"></</span><span class="MetaTag">h3</span><span class="MetaTag">></span></span>
<span class="line-numbers"> 5 </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"> 6 </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">h_1</span><span class="String">"</span></span></span><span class="MetaTag">></span></span>Inner Section<span class="MetaTag"><span class="MetaTag"></</span><span class="MetaTag">h2</span><span class="MetaTag">></span></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>
<span class="line-numbers"> 9 </span> <span class="MetaTag"><span class="MetaTag"></</span><span class="MetaTag">div</span><span class="MetaTag">></span></span>
<span class="line-numbers"> 10 </span> <span class="MetaTag"><span class="MetaTag"></</span><span class="MetaTag">div</span><span class="MetaTag">></span></span>
</pre>
<p>Everything is fine <em>except</em> for the header level: the heading "Inner Section" is of level 2, but it should be level 4!</p>
<p>This happens because the inner section is evaluated <em>before</em> the <code>nest_section</code> macro: after all, we ask for it ourselves when we call the <code>value</code> method inside the macro definition. When the value is expanded, there are no outer sections <em>yet</em>.</p>
<p>To avoid this unwanted behavior, we can use the <code>raw_value</code> method instead, that returns the first parameter converted back to a Glyph code string.</p>
<div class="tip">
<span class="note-title">Tip</span>To be on the safe side, always use <code>raw_*</code> methods when interpreting.
</div>
<p>To access raw values, use the following methods:</p>
<ul>
<li><code>raw_parameter</code> (or <code>raw_param</code>): Returns the raw parameter value of the parameter specified by number.</li>
<li><code>raw_value</code>: Returns the first raw parameter value (i.e. like <code>raw_parameter(0)</code>).</li>
<li><code>raw_attribute</code> (or <code>raw_attr</code>): Returns the attribute value of the attribute specified by name.</li>
</ul>
</div>
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