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lists.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>lists</title>
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<h1 id="lists">Lists</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">list</span> <span class="dv">1</span> <span class="dv">2</span> <span class="dv">3</span>)</a>
<a class="sourceLine" id="cb1-2" title="2"><span class="co">;; => (1 2 3)</span></a>
<a class="sourceLine" id="cb1-3" title="3"></a>
<a class="sourceLine" id="cb1-4" title="4">(<span class="kw">cons</span> <span class="dv">4</span> (<span class="kw">list</span> <span class="dv">1</span> <span class="dv">2</span> <span class="dv">3</span>))</a>
<a class="sourceLine" id="cb1-5" title="5"><span class="co">;; => (4 1 2 3)</span></a>
<a class="sourceLine" id="cb1-6" title="6"></a>
<a class="sourceLine" id="cb1-7" title="7">(<span class="kw">cons</span> <span class="dv">1</span> ())</a>
<a class="sourceLine" id="cb1-8" title="8"><span class="co">;; => (1)</span></a>
<a class="sourceLine" id="cb1-9" title="9"></a>
<a class="sourceLine" id="cb1-10" title="10">(<span class="kw">cons</span> <span class="dv">1</span> (<span class="kw">cons</span> <span class="dv">2</span> ()))</a>
<a class="sourceLine" id="cb1-11" title="11"><span class="co">;; => (1 2)</span></a></code></pre></div>
<p>You can create lists with <code>list</code></p>
<p>Lists internally are “cons cells”. You can see how we can construct a list manually by calling <code>cons</code>.</p>
<p>You can think of cons cells as a box that you can put two things in.</p>
<div class="sourceCode" id="cb2"><pre class="sourceCode commonlisp"><code class="sourceCode commonlisp"><a class="sourceLine" id="cb2-1" title="1">(<span class="kw">first</span> (<span class="kw">list</span> <span class="dv">7</span> <span class="dv">8</span> <span class="dv">9</span>))</a>
<a class="sourceLine" id="cb2-2" title="2"><span class="co">;; => 7</span></a>
<a class="sourceLine" id="cb2-3" title="3"></a>
<a class="sourceLine" id="cb2-4" title="4">(<span class="kw">last</span> (<span class="kw">list</span> <span class="dv">8</span> <span class="dv">5</span> <span class="st">"foobar"</span>))</a>
<a class="sourceLine" id="cb2-5" title="5"><span class="co">;; => ("foobar")</span></a>
<a class="sourceLine" id="cb2-6" title="6"></a>
<a class="sourceLine" id="cb2-7" title="7">(<span class="kw">butlast</span> (<span class="kw">list</span> <span class="dv">1</span> <span class="dv">2</span> <span class="dv">3</span>))</a>
<a class="sourceLine" id="cb2-8" title="8"><span class="co">;; => (1 2)</span></a>
<a class="sourceLine" id="cb2-9" title="9"></a>
<a class="sourceLine" id="cb2-10" title="10">(<span class="kw">first</span> (<span class="kw">last</span> (<span class="kw">list</span> <span class="st">"Chris"</span> <span class="st">"Alex"</span> <span class="st">"Dave"</span>)))</a>
<a class="sourceLine" id="cb2-11" title="11"><span class="co">;; => "Dave"</span></a>
<a class="sourceLine" id="cb2-12" title="12"></a>
<a class="sourceLine" id="cb2-13" title="13">(<span class="kw">rest</span> (<span class="kw">list</span> <span class="dv">1</span> <span class="dv">2</span> <span class="dv">3</span>))</a>
<a class="sourceLine" id="cb2-14" title="14"><span class="co">;; => (2 3)</span></a>
<a class="sourceLine" id="cb2-15" title="15"></a>
<a class="sourceLine" id="cb2-16" title="16">(<span class="kw">third</span> (<span class="kw">list</span> <span class="dv">1</span> <span class="dv">2</span>))</a>
<a class="sourceLine" id="cb2-17" title="17"><span class="co">;; => NIL</span></a>
<a class="sourceLine" id="cb2-18" title="18"></a>
<a class="sourceLine" id="cb2-19" title="19">(<span class="kw">nth</span> <span class="dv">3</span> (<span class="kw">list</span> <span class="dv">3</span> <span class="dv">4</span> <span class="dv">5</span> <span class="dv">6</span>))</a>
<a class="sourceLine" id="cb2-20" title="20"><span class="co">;; => 6</span></a></code></pre></div>
<p>There are convenient accessor functions.</p>
<div class="sourceCode" id="cb3"><pre class="sourceCode commonlisp"><code class="sourceCode commonlisp"><a class="sourceLine" id="cb3-1" title="1">(<span class="kw">append</span> (<span class="kw">list</span> <span class="dv">1</span> <span class="dv">2</span> <span class="dv">3</span>) (<span class="kw">list</span> <span class="dv">4</span> <span class="dv">5</span> <span class="dv">6</span>))</a>
<a class="sourceLine" id="cb3-2" title="2"><span class="co">;; => (1 2 3 4 5 6)</span></a></code></pre></div>
<p>We can append lists together</p>
<div class="sourceCode" id="cb4"><pre class="sourceCode commonlisp"><code class="sourceCode commonlisp"><a class="sourceLine" id="cb4-1" title="1">(<span class="kw">butlast</span> (<span class="kw">list</span> <span class="dv">1</span> <span class="dv">2</span> <span class="dv">3</span>))</a>
<a class="sourceLine" id="cb4-2" title="2"><span class="co">;; => (1 2)</span></a></code></pre></div>
<p>Returns everything but the last element.</p>
<div class="sourceCode" id="cb5"><pre class="sourceCode commonlisp"><code class="sourceCode commonlisp"><a class="sourceLine" id="cb5-1" title="1">(<span class="kw">subseq</span> (<span class="kw">list</span> <span class="st">"a"</span> <span class="st">"b"</span> <span class="st">"c"</span> <span class="st">"d"</span> <span class="st">"e"</span> <span class="st">"f"</span>) <span class="dv">1</span> <span class="dv">3</span>)</a>
<a class="sourceLine" id="cb5-2" title="2"><span class="co">;; => ("b" "c")</span></a>
<a class="sourceLine" id="cb5-3" title="3"></a>
<a class="sourceLine" id="cb5-4" title="4">(<span class="kw">subseq</span> (<span class="kw">list</span> <span class="st">"a"</span> <span class="st">"b"</span> <span class="st">"c"</span> <span class="st">"d"</span> <span class="st">"e"</span> <span class="st">"f"</span>) <span class="dv">3</span>)</a>
<a class="sourceLine" id="cb5-5" title="5"><span class="co">;; => ("d" "e" "f")</span></a>
<a class="sourceLine" id="cb5-6" title="6"></a>
<a class="sourceLine" id="cb5-7" title="7">(<span class="kw">subseq</span> (<span class="kw">list</span> <span class="dv">1</span> <span class="dv">2</span> <span class="dv">3</span>) <span class="dv">0</span> <span class="dv">1337</span>)</a>
<a class="sourceLine" id="cb5-8" title="8"><span class="co">;; WILL BLOW UP WITH LEETNESS</span></a></code></pre></div>
<ul>
<li><code>subseq</code> returns the elements of a list from the first index to the last in a list (last index is exlusive).</li>
<li>The last index is optional.</li>
<li>It’ll blow up if the list isn’t long enough</li>
</ul>
<div class="sourceCode" id="cb6"><pre class="sourceCode commonlisp"><code class="sourceCode commonlisp"><a class="sourceLine" id="cb6-1" title="1">(<span class="kw">length</span> (<span class="kw">list</span> <span class="dv">1</span> <span class="dv">2</span> <span class="dv">3</span> <span class="dv">4</span> <span class="dv">5</span> <span class="dv">6</span>))</a>
<a class="sourceLine" id="cb6-2" title="2"><span class="co">;; => 6</span></a>
<a class="sourceLine" id="cb6-3" title="3"></a>
<a class="sourceLine" id="cb6-4" title="4">(<span class="kw">reverse</span> (<span class="kw">list</span> <span class="dv">6</span> <span class="dv">5</span> <span class="dv">4</span> <span class="dv">3</span> <span class="dv">2</span> <span class="dv">1</span>))</a>
<a class="sourceLine" id="cb6-5" title="5"><span class="co">;; => (1 2 3 4 5 6)</span></a></code></pre></div>
<p><code>length</code> gives you the length of a list <code>reverse</code> reverses a list</p>
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