blog/content/post/2008/08/04/2008-08-04-00000989.md

---
title: 等価性
author: kazu634
date: 2008-08-04
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categories:
  - gauche
  - Lisp

---
<div class="section">
<p>
    「二つのオブジェクトAとBが等しいとはどういうことでしょうか？」これには色々な意味があるよ。
</p>

<h4>
    内容が同じという場合
</h4>

<p>
    二つのリストがあった場合、それぞれの要素を順に比較し、全て等しければ元のリストも等しいという立場での比較。
</p>

<pre class="syntax-highlight">
gosh&#62; <span class="synSpecial">(</span><span class="synStatement">equal</span>? <span class="synSpecial">(</span><span class="synStatement">list</span> <span class="synConstant">1</span> <span class="synConstant">2</span> <span class="synConstant">3</span><span class="synSpecial">)</span> <span class="synSpecial">(</span><span class="synStatement">list</span> <span class="synConstant">1</span> <span class="synConstant">2</span> <span class="synConstant">3</span><span class="synSpecial">))</span>
#<span class="synStatement">t</span>
gosh&#62; <span class="synSpecial">(</span><span class="synStatement">equal</span>? <span class="synSpecial">(</span><span class="synStatement">list</span> <span class="synConstant">1</span> <span class="synConstant">2</span> <span class="synSpecial">(</span><span class="synStatement">list</span> <span class="synConstant">3</span> <span class="synConstant">4</span><span class="synSpecial">)</span> <span class="synConstant">5</span><span class="synSpecial">)</span> <span class="synSpecial">(</span><span class="synStatement">cons</span> <span class="synConstant">1</span> <span class="synSpecial">(</span><span class="synStatement">cons</span> <span class="synConstant">2</span> <span class="synSpecial">'((</span>3 4<span class="synSpecial">)</span> . <span class="synSpecial">(</span>5<span class="synSpecial">)))))</span>
#<span class="synStatement">t</span>
gosh&#62; <span class="synSpecial">(</span><span class="synStatement">equal</span>? <span class="synSpecial">(</span><span class="synStatement">list</span> <span class="synConstant">1</span> <span class="synConstant">2</span> <span class="synConstant">3</span><span class="synSpecial">)</span> <span class="synSpecial">(</span><span class="synStatement">list</span> <span class="synConstant">1</span> <span class="synConstant">2</span> <span class="synConstant">4</span><span class="synSpecial">))</span>
#f
</pre>

<h4>
    入れ物が同じ
</h4>

<p>
    他の値を入れておく入れ物の同一性を調べるもの。C言語を知っている人は、eq?はオブジェクトの「アドレス」を比較していると考えていい。
</p>

<pre class="syntax-highlight">
gosh&#62; <span class="synSpecial">(</span><span class="synStatement">eq</span>? <span class="synSpecial">(</span><span class="synStatement">cons</span> <span class="synConstant">1</span> <span class="synConstant">2</span><span class="synSpecial">)</span> <span class="synSpecial">(</span><span class="synStatement">cons</span> <span class="synConstant">1</span> <span class="synConstant">2</span><span class="synSpecial">))</span>
#f
gosh&#62; <span class="synSpecial">(</span>define p <span class="synSpecial">(</span><span class="synStatement">cons</span> <span class="synConstant">1</span> <span class="synConstant">2</span><span class="synSpecial">))</span>
p
gosh&#62; <span class="synSpecial">(</span><span class="synStatement">eq</span>? p p<span class="synSpecial">)</span>
#<span class="synStatement">t</span>
</pre>

<h4>
    数値として同じ
</h4>

<p>
    数値として比較する場合。
</p>

<pre class="syntax-highlight">
gosh&#62; <span class="synSpecial">(</span>eqv? <span class="synConstant">1</span> <span class="synConstant">1</span><span class="synSpecial">)</span>
#<span class="synStatement">t</span>
gosh&#62; <span class="synSpecial">(</span>eqv? <span class="synConstant">1.0</span> <span class="synConstant">1.0</span><span class="synSpecial">)</span>
#<span class="synStatement">t</span>
gosh&#62; <span class="synSpecial">(</span>eqv? <span class="synConstant">1</span> <span class="synConstant">1.0</span><span class="synSpecial">)</span>
#f
gosh&#62; <span class="synSpecial">(</span><span class="synStatement">=</span> <span class="synConstant">1</span> <span class="synConstant">1.0</span><span class="synSpecial">)</span>
#<span class="synStatement">t</span>
gosh&#62; <span class="synSpecial">(</span><span class="synStatement">char=</span>? #\a #\a<span class="synSpecial">)</span>
#<span class="synStatement">t</span>
gosh&#62; <span class="synSpecial">(</span><span class="synStatement">char=</span>? #\a <span class="synType">#\A</span><span class="synSpecial">)</span>
#f
gosh&#62; <span class="synSpecial">(</span><span class="synStatement">string=</span>? <span class="synConstant">&#34;abc&#34;</span> <span class="synConstant">&#34;abc&#34;</span><span class="synSpecial">)</span>
#<span class="synStatement">t</span>
gosh&#62; <span class="synSpecial">(</span><span class="synStatement">string=</span>? <span class="synConstant">&#34;abc&#34;</span> <span class="synConstant">&#34;ABC&#34;</span><span class="synSpecial">)</span>
#f
</pre>

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