blog/content/post/2008/09/24/2008-09-24-00001035.md

---
title: 自力でmaxを定義する – なにかうまくいかないや
author: kazu634
date: 2008-09-24
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categories:
  - gauche
  - Lisp

---
<div class="section">
<p>
    とりあえず作ってみた:
</p>

<pre class="syntax-highlight">
<span class="synSpecial">(</span>define <span class="synSpecial">(</span>my_length lis<span class="synSpecial">)</span>
<span class="synSpecial">(</span><span class="synStatement">if</span> <span class="synSpecial">(</span><span class="synStatement">null</span>? lis<span class="synSpecial">)</span>
<span class="synConstant"></span>
<span class="synSpecial">(</span><span class="synStatement">+</span> <span class="synConstant">1</span> <span class="synSpecial">(</span>my_length <span class="synSpecial">(</span><span class="synStatement">cdr</span> lis<span class="synSpecial">)))))</span>
<span class="synSpecial">(</span>define <span class="synSpecial">(</span>my_max<span class="synStatement"> . </span>lis<span class="synSpecial">)</span>
<span class="synSpecial">(</span><span class="synStatement">cond</span> [<span class="synSpecial">(</span><span class="synStatement">null</span>? lis<span class="synSpecial">)</span> #f]
[<span class="synSpecial">(</span><span class="synStatement">=</span> <span class="synSpecial">(</span>my_length lis<span class="synSpecial">)</span> <span class="synConstant">1</span><span class="synSpecial">)</span> <span class="synSpecial">(</span><span class="synStatement">car</span> lis<span class="synSpecial">)</span>]
[<span class="synSpecial">(</span><span class="synStatement">=</span> <span class="synSpecial">(</span>my_length lis<span class="synSpecial">)</span> <span class="synConstant">2</span><span class="synSpecial">)</span> <span class="synSpecial">(</span><span class="synStatement">cond</span> [<span class="synSpecial">(</span><span class="synStatement">&#60;=</span> <span class="synSpecial">(</span><span class="synStatement">car</span> lis<span class="synSpecial">)</span> <span class="synSpecial">(</span><span class="synStatement">cadr</span> lis<span class="synSpecial">))</span> <span class="synSpecial">(</span><span class="synStatement">cadr</span> lis<span class="synSpecial">)</span>]
[<span class="synSpecial">(</span><span class="synStatement">&#62;=</span> <span class="synSpecial">(</span><span class="synStatement">car</span> lis<span class="synSpecial">)</span> <span class="synSpecial">(</span><span class="synStatement">cadr</span> lis<span class="synSpecial">))</span> <span class="synSpecial">(</span><span class="synStatement">car</span> lis<span class="synSpecial">)</span>]<span class="synSpecial">)</span>]
[<span class="synSpecial">(</span><span class="synStatement">&#62;=</span> <span class="synSpecial">(</span>my_length lis<span class="synSpecial">)</span> <span class="synConstant">3</span><span class="synSpecial">)</span> <span class="synSpecial">(</span><span class="synStatement">cond</span> [<span class="synSpecial">(</span><span class="synStatement">&#60;=</span> <span class="synSpecial">(</span><span class="synStatement">car</span> lis<span class="synSpecial">)</span> <span class="synSpecial">(</span><span class="synStatement">cadr</span> lis<span class="synSpecial">))</span> <span class="synSpecial">(</span>my_max <span class="synSpecial">(</span><span class="synStatement">cons</span> <span class="synSpecial">(</span><span class="synStatement">cadr</span> lis<span class="synSpecial">)</span> <span class="synSpecial">(</span><span class="synStatement">cddr</span> lis<span class="synSpecial">)))</span>]
[<span class="synSpecial">(</span><span class="synStatement">&#62;=</span> <span class="synSpecial">(</span><span class="synStatement">car</span> lis<span class="synSpecial">)</span> <span class="synSpecial">(</span><span class="synStatement">cadr</span> lis<span class="synSpecial">))</span> <span class="synSpecial">(</span>my_max <span class="synSpecial">(</span><span class="synStatement">cons</span> <span class="synSpecial">(</span><span class="synStatement">car</span> lis<span class="synSpecial">)</span> <span class="synSpecial">(</span><span class="synStatement">cddr</span> lis<span class="synSpecial">)))</span>]<span class="synSpecial">)</span>]<span class="synSpecial">))</span>
</pre>

<p>
    でもこれだと、
</p>

<pre class="syntax-highlight">
gosh&#62; <span class="synSpecial">(</span>my_max <span class="synConstant">1</span> <span class="synConstant">2</span> <span class="synConstant">34</span> <span class="synConstant">5</span> <span class="synConstant">6</span><span class="synSpecial">)</span>
<span class="synSpecial">(</span><span class="synConstant">2</span> <span class="synConstant">34</span> <span class="synConstant">5</span> <span class="synConstant">6</span><span class="synSpecial">)</span>
</pre>

<p>
    可変長引数の扱いについてもう一度見直してみようっと。可変長引数じゃなければ（=引数が「. lis」じゃなくて「lis」にして、リストを引数に渡してあげると）、希望通りの動作になる。たぶん可変長引数に特有のことなんだと思う。たぶんねー。
</p>

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