contents/glyph/book/text_editing/conditionals.html
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----- title: "Glyph – Conditional Macros" content-type: page ----- <nav class="navigation"><a href="/glyph/book/text_editing/inclusions.html">← Content Reuse</a> | <a href="/glyph/book/index.html">Contents</a> | <a href="/glyph/book/text_editing/evaluation.html">Simple Programming and Code Evaluation →</a></nav> <p>Sometimes you may want text to be included in a document only if certain conditions are satisfied. For example, you may want to display a disclaimer section only if the document is a draft (see the <a href="/glyph/book/config/document.html#s_document_draft"><code>document.draft</code></a> setting), or use a particular stylesheet only if when you generate a <span class="caps">PDF</span> document.</p> <p>To do so, you can use the <a href="/glyph/book/macros/macros_core.html#m_condition"><code>condition</code></a> macro (aliased by <code>?</code>), and a set of additional macros that can be used as conditional operators i.e.:</p> <ul> <li><a href="/glyph/book/macros/macros_core.html#m_eq"><code>eq</code></a> macro</li> <li><a href="/glyph/book/macros/macros_core.html#m_not"><code>not</code></a> macro</li> <li><a href="/glyph/book/macros/macros_core.html#m_and"><code>and</code></a> macro</li> <li><a href="/glyph/book/macros/macros_core.html#m_or"><code>or</code></a> macro</li> </ul> <p>Consider the following code:</p> <div class="CodeRay"> <div class="code"><pre><span class="line-numbers"><a href="#n1" name="n1">1</a></span>?[$[document.draft]| <span class="line-numbers"><a href="#n2" name="n2">2</a></span>This is a first draft of the Glyph Book| <span class="line-numbers"><a href="#n3" name="n3">3</a></span>This is the official version of the Glyph Book]</pre></div> </div> <p>In this case, if <code>document.draft</code> is set to <code>true</code>, “This is a first draft of the Glyph Book” will be displayed; if not, “This is the official version of the Glyph Book” will be displayed instead.</p> <p>The <a href="/glyph/book/macros/macros_core.html#m_condition"><code>condition</code></a> macro takes up to three parameters:</p> <ol> <li>the condition to evaluate</li> <li>the text to include in the document only if the condition is satisfied.</li> <li><em>(Optional)</em> the text to include in the document if the condition is <em>not</em> satisfied.</li> </ol> <p>Note that <em>all</em> parameters can contain macros, of course, so you can write things like:</p> <div class="CodeRay"> <div class="code"><pre><span class="line-numbers"><a href="#n1" name="n1">1</a></span>?[and[ <span class="line-numbers"><a href="#n2" name="n2">2</a></span> eq[$[document.output]|pdf] <span class="line-numbers"><a href="#n3" name="n3">3</a></span> | <span class="line-numbers"><a href="#n4" name="n4">4</a></span> eq[$[tools.pdf_generator]|prince] <span class="line-numbers"><a href="#n5" name="n5">5</a></span> ] <span class="line-numbers"><a href="#n6" name="n6">6</a></span> | <span class="line-numbers"><a href="#n7" name="n7">7</a></span> style[pagination.css]]</pre></div> </div> <p>In this case, the <code>pagination.css</code> stylesheet is included only when you're generating a PDF document using Prince XML.</p> <section class="section"> <header><h1 id="h_42" class="toc">Results of conditional expressions</h1></header> <p>The <a href="/glyph/book/macros/macros_core.html#m_condition"><code>condition</code></a> macro in Glyph works in a similar way as conditionals in programming languages: if the conditional expression (supplied as first parameter) is satisfied then the second parameter is executed or displayed. But when is a conditional expression satisfied? Glyph is a simple mini-language to perform text manipulation, and has no types, it can only understand text, therefore:</p> <ul> <li>A conditional expression is satisfied if it evaluates to a non-empty string except “false”.</li> <li>A conditional expression is not satisfied if it evaluates to an empty string or the string “false”.</li> </ul> </section> <nav class="navigation"><a href="/glyph/book/text_editing/inclusions.html">← Content Reuse</a> | <a href="/glyph/book/index.html">Contents</a> | <a href="/glyph/book/text_editing/evaluation.html">Simple Programming and Code Evaluation →</a></nav> |