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<h1>Parameters and Attributes</h1>
<h2>Glyph</h2>
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<nav 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></nav>
<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>
<section class="section">
<header><h1 id="expanded_values">Accessing Expanded Values</h1></header>
<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>
</section>
<section class="section">
<header><h1 id="h_89">Accessing Raw Values</h1></header>
<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>
<div class="CodeRay">
<div class="code"><pre><span class="no"> 1</span> macro <span class="sy">:nest_section</span> <span class="r">do</span>
<span class="no"> 2</span> interpret <span class="s"><span class="dl">%{</span><span class="k">section[
<span class="no"> 3</span> @title[A]
<span class="no"> 4</span> section[
<span class="no"> 5</span> @title[B]
<span class="no"> 6</span> </span><span class="il"><span class="idl">#{</span>value<span class="idl">}</span></span><span class="k">
<span class="no"> 7</span> ]
<span class="no"> 8</span> ]</span><span class="dl">}</span></span>
<span class="no"> 9</span> <span class="r">end</span></pre></div>
</div>
<p>And suppose to use it as follows:</p>
<div class="CodeRay">
<div class="code"><pre><span class="no">1</span> nest_section[
<span class="no">2</span> section[
<span class="no">3</span> <span class="iv">@title</span>[<span class="co">Inner</span> <span class="co">Section</span>]
<span class="no">4</span> ...
<span class="no">5</span> ]
<span class="no">6</span> ]</pre></div>
</div>
<p>It produces the following HTML code:</p>
<div class="CodeRay">
<div class="code"><pre><span class="no"> 1</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"> 2</span> <span class="ta"><h2</span> <span class="an">id</span>=<span class="s"><span class="dl">"</span><span class="k">h_2</span><span class="dl">"</span></span><span class="ta">></span>A<span class="ta"></h2></span>
<span class="no"> 3</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"> 4</span> <span class="ta"><h3</span> <span class="an">id</span>=<span class="s"><span class="dl">"</span><span class="k">h_3</span><span class="dl">"</span></span><span class="ta">></span>B<span class="ta"></h3></span>
<span class="no"> 5</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"> 6</span> <span class="ta"><h2</span> <span class="an">id</span>=<span class="s"><span class="dl">"</span><span class="k">h_1</span><span class="dl">"</span></span><span class="ta">></span>Inner Section<span class="ta"></h2></span>
<span class="no"> 7</span> ...
<span class="no"> 8</span> <span class="ta"></div></span>
<span class="no"> 9</span> <span class="ta"></div></span>
<span class="no"><strong>10</strong></span> <span class="ta"></div></span></pre></div>
</div>
<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>
<aside class="tip">
<span class="note-title">Tip</span>To be on the safe side, always use <code>raw_*</code> methods when interpreting.
</aside>
<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>
</section>
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