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<!DOCTYPE html>
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<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>values</title>
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<body>
<h1 id="values">Values</h1>
<div class="sourceCode" id="cb1"><pre class="sourceCode lisp"><code class="sourceCode commonlisp"><a class="sourceLine" id="cb1-1" title="1">(<span class="kw">princ</span> (<span class="kw">concatenate</span> 'string <span class="st">"hello, "</span> <span class="st">"world"</span>))</a>
<a class="sourceLine" id="cb1-2" title="2"><span class="co">;; => hello, world</span></a>
<a class="sourceLine" id="cb1-3" title="3"><span class="co">;;</span></a>
<a class="sourceLine" id="cb1-4" title="4"><span class="co">;; "hello, world"</span></a></code></pre></div>
<ul>
<li><code>concatenate</code> can be used with different types, we need to specify the output type with the <code>'string</code> symbol.</li>
</ul>
<div class="sourceCode" id="cb2"><pre class="sourceCode lisp"><code class="sourceCode commonlisp"><a class="sourceLine" id="cb2-1" title="1">(<span class="kw">princ</span> (<span class="kw">format</span> <span class="kw">nil</span> <span class="st">"1 + 1 = ~a"</span> (<span class="op">+</span> <span class="dv">1</span> <span class="dv">1</span>)))</a>
<a class="sourceLine" id="cb2-2" title="2"><span class="co">;; => 1 + 1 = 2</span></a>
<a class="sourceLine" id="cb2-3" title="3"><span class="co">;;</span></a>
<a class="sourceLine" id="cb2-4" title="4"><span class="co">;; "1 + 1 = 2"</span></a></code></pre></div>
<ul>
<li><code>format</code> is a function for creating formatted strings</li>
<li><code>nil</code> tells <code>format</code> to evaluate to the string it creates</li>
<li><code>~a</code> is a <em>format directive</em>. It prints the next argument to <code>format</code> _a_esthetically.</li>
<li>All <code>format</code> directives start with <code>~</code></li>
</ul>
<div class="sourceCode" id="cb3"><pre class="sourceCode lisp"><code class="sourceCode commonlisp"><a class="sourceLine" id="cb3-1" title="1">(<span class="kw">format</span> <span class="kw">t</span> <span class="st">"~a"</span> (<span class="op">/</span> <span class="fl">4.0</span> <span class="fl">5.0</span>))</a>
<a class="sourceLine" id="cb3-2" title="2"><span class="co">;; => 0.8</span></a>
<a class="sourceLine" id="cb3-3" title="3"><span class="co">;;</span></a>
<a class="sourceLine" id="cb3-4" title="4"><span class="co">;; NIL</span></a></code></pre></div>
<ul>
<li>floating point numbers have a <code>.</code> in them</li>
<li>when the second argument to <code>format</code> is <code>t</code> it prints the string to standard out</li>
<li>in this case <code>format</code> evaluates to <code>nil</code></li>
</ul>
<div class="sourceCode" id="cb4"><pre class="sourceCode lisp"><code class="sourceCode commonlisp"><a class="sourceLine" id="cb4-1" title="1">(<span class="op">+</span> <span class="dv">1</span>/<span class="dv">2</span> <span class="dv">1</span>/<span class="dv">4</span>)</a>
<a class="sourceLine" id="cb4-2" title="2"><span class="co">;; => 3/4</span></a></code></pre></div>
<ul>
<li>Lisp has rational numbers as a separate type - they are written with a <code>/</code> between the numerator and the denomenator.</li>
</ul>
<div class="sourceCode" id="cb5"><pre class="sourceCode lisp"><code class="sourceCode commonlisp"><a class="sourceLine" id="cb5-1" title="1">(<span class="kw">and</span> <span class="kw">t</span> <span class="kw">nil</span>)</a>
<a class="sourceLine" id="cb5-2" title="2"><span class="co">;; => NIL</span></a>
<a class="sourceLine" id="cb5-3" title="3"></a>
<a class="sourceLine" id="cb5-4" title="4">(<span class="kw">and</span> <span class="st">"ada"</span> <span class="dv">5</span> <span class="st">"alonzo"</span>)</a>
<a class="sourceLine" id="cb5-5" title="5"><span class="co">;; => "alonzo"</span></a>
<a class="sourceLine" id="cb5-6" title="6"></a>
<a class="sourceLine" id="cb5-7" title="7">(<span class="kw">and</span>)</a>
<a class="sourceLine" id="cb5-8" title="8"><span class="co">;; => T</span></a>
<a class="sourceLine" id="cb5-9" title="9"></a>
<a class="sourceLine" id="cb5-10" title="10">(<span class="kw">or</span> <span class="kw">t</span> <span class="kw">nil</span>)</a>
<a class="sourceLine" id="cb5-11" title="11"><span class="co">;; => T</span></a>
<a class="sourceLine" id="cb5-12" title="12"></a>
<a class="sourceLine" id="cb5-13" title="13">(<span class="kw">or</span> <span class="kw">nil</span> <span class="st">"lucy"</span> <span class="kw">nil</span>)</a>
<a class="sourceLine" id="cb5-14" title="14"><span class="co">;; => "barry"</span></a>
<a class="sourceLine" id="cb5-15" title="15"></a>
<a class="sourceLine" id="cb5-16" title="16">(<span class="kw">or</span>)</a>
<a class="sourceLine" id="cb5-17" title="17"><span class="co">;; => NIL</span></a>
<a class="sourceLine" id="cb5-18" title="18"></a>
<a class="sourceLine" id="cb5-19" title="19">(<span class="kw">not</span> <span class="kw">nil</span>)</a>
<a class="sourceLine" id="cb5-20" title="20"><span class="co">;; => T</span></a>
<a class="sourceLine" id="cb5-21" title="21"></a>
<a class="sourceLine" id="cb5-22" title="22">(<span class="kw">not</span> <span class="st">"amy"</span>)</a>
<a class="sourceLine" id="cb5-23" title="23"><span class="co">;; => NIL</span></a></code></pre></div>
<ul>
<li>There is no true or false - only <code>t</code> and <code>nil</code></li>
<li><code>t</code> and <code>nil</code> are special symbols; they always evaluate to themselves</li>
<li>anything that’s not <code>nil</code> is treated as true!</li>
<li><code>and</code> and <code>or</code> can take multiple values</li>
<li><code>and</code> returns the first <code>nil</code> or the last non-<code>nil</code> argument</li>
<li><code>or</code> returns the first non-<code>nil</code> argument</li>
<li><code>not</code> will return <code>nil</code> for all non-<code>nil</code> values, and <code>t</code> for <code>nil</code></li>
</ul>
<h3 id="see-also">See also</h3>
<p><a href="http://www.lispworks.com/documentation/lw50/CLHS/Body/f_format.htm">Common Lisp Hyperspec: FORMAT</a> <a href="http://www.lispworks.com/documentation/lw50/CLHS/Body/22_c.htm">Common Lisp Hyperspec: Formatted output</a> <a href="http://www.gigamonkeys.com/book/a-few-format-recipes.html">Practical Common Lisp: A Few Format Recipes</a></p>
</body>
</html>