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variables.html
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<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml" lang="" xml:lang="">
<head>
<meta charset="utf-8" />
<meta name="generator" content="pandoc" />
<meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=yes" />
<title>variables</title>
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<body>
<h1 id="global-variables">Global variables</h1>
<div class="sourceCode" id="cb1"><pre class="sourceCode commonlisp"><code class="sourceCode commonlisp"><a class="sourceLine" id="cb1-1" title="1">(<span class="kw">defparameter</span><span class="fu"> *a* </span><span class="st">"intitial"</span>)</a>
<a class="sourceLine" id="cb1-2" title="2"><span class="co">;; => *A*</span></a>
<a class="sourceLine" id="cb1-3" title="3"></a>
<a class="sourceLine" id="cb1-4" title="4">(<span class="kw">princ</span> *a*)</a>
<a class="sourceLine" id="cb1-5" title="5"><span class="co">;; => intitial</span></a>
<a class="sourceLine" id="cb1-6" title="6"><span class="co">;;</span></a>
<a class="sourceLine" id="cb1-7" title="7"><span class="co">;; "intitial"</span></a></code></pre></div>
<ul>
<li>the surrounding asterisks (or ‘earmuffs’) are a convention to indicate that the variable is DYNAMIC or SPECIAL. More later.</li>
</ul>
<div class="sourceCode" id="cb2"><pre class="sourceCode commonlisp"><code class="sourceCode commonlisp"><a class="sourceLine" id="cb2-1" title="1">(<span class="kw">setf</span> *a* <span class="st">"updated"</span>)</a>
<a class="sourceLine" id="cb2-2" title="2"><span class="co">;; => "updated"</span></a>
<a class="sourceLine" id="cb2-3" title="3"></a>
<a class="sourceLine" id="cb2-4" title="4">(<span class="kw">princ</span> *a*)</a>
<a class="sourceLine" id="cb2-5" title="5"><span class="co">;; => updated</span></a>
<a class="sourceLine" id="cb2-6" title="6"><span class="co">;;</span></a>
<a class="sourceLine" id="cb2-7" title="7"><span class="co">;; "updated"</span></a></code></pre></div>
<ul>
<li>A variable can be updated by using <code>setf</code>.</li>
</ul>
<div class="sourceCode" id="cb3"><pre class="sourceCode commonlisp"><code class="sourceCode commonlisp"><a class="sourceLine" id="cb3-1" title="1">(<span class="kw">setf</span> *a* <span class="dv">42</span>)</a>
<a class="sourceLine" id="cb3-2" title="2"><span class="co">;; => 42</span></a>
<a class="sourceLine" id="cb3-3" title="3"></a>
<a class="sourceLine" id="cb3-4" title="4">(<span class="kw">princ</span> *a*)</a>
<a class="sourceLine" id="cb3-5" title="5"><span class="co">;; => 42</span></a>
<a class="sourceLine" id="cb3-6" title="6"><span class="co">;;</span></a>
<a class="sourceLine" id="cb3-7" title="7"><span class="co">;; 42</span></a></code></pre></div>
<ul>
<li>Common lisp is dynamically typed so we are free to change variables to different types</li>
</ul>
</body>
</html>