99 lines
6.8 KiB
Markdown
99 lines
6.8 KiB
Markdown
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---
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title: 等価性
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author: kazu634
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date: 2008-08-04
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url: /2008/08/04/_1063/
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wordtwit_post_info:
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- 'O:8:"stdClass":13:{s:6:"manual";b:0;s:11:"tweet_times";i:1;s:5:"delay";i:0;s:7:"enabled";i:1;s:10:"separation";s:2:"60";s:7:"version";s:3:"3.7";s:14:"tweet_template";b:0;s:6:"status";i:2;s:6:"result";a:0:{}s:13:"tweet_counter";i:2;s:13:"tweet_log_ids";a:1:{i:0;i:4187;}s:9:"hash_tags";a:0:{}s:8:"accounts";a:1:{i:0;s:7:"kazu634";}}'
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categories:
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- gauche
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- Lisp
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---
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<div class="section">
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<p>
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「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。
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</p>
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<h4>
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内容が同じという場合
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</h4>
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<p>
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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。
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</p>
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<pre class="syntax-highlight">
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gosh> <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>
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#<span class="synStatement">t</span>
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gosh> <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>
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#<span class="synStatement">t</span>
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gosh> <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>
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#f
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</pre>
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<h4>
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入れ物が同じ
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</h4>
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<p>
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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。
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</p>
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<pre class="syntax-highlight">
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gosh> <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>
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#f
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gosh> <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>
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p
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gosh> <span class="synSpecial">(</span><span class="synStatement">eq</span>? p p<span class="synSpecial">)</span>
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#<span class="synStatement">t</span>
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</pre>
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<h4>
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数値として同じ
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</h4>
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<p>
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数値として比較する場合。
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</p>
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<pre class="syntax-highlight">
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gosh> <span class="synSpecial">(</span>eqv? <span class="synConstant">1</span> <span class="synConstant">1</span><span class="synSpecial">)</span>
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#<span class="synStatement">t</span>
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gosh> <span class="synSpecial">(</span>eqv? <span class="synConstant">1.0</span> <span class="synConstant">1.0</span><span class="synSpecial">)</span>
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#<span class="synStatement">t</span>
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gosh> <span class="synSpecial">(</span>eqv? <span class="synConstant">1</span> <span class="synConstant">1.0</span><span class="synSpecial">)</span>
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#f
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gosh> <span class="synSpecial">(</span><span class="synStatement">=</span> <span class="synConstant">1</span> <span class="synConstant">1.0</span><span class="synSpecial">)</span>
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#<span class="synStatement">t</span>
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gosh> <span class="synSpecial">(</span><span class="synStatement">char=</span>? #\a #\a<span class="synSpecial">)</span>
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#<span class="synStatement">t</span>
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gosh> <span class="synSpecial">(</span><span class="synStatement">char=</span>? #\a <span class="synType">#\A</span><span class="synSpecial">)</span>
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#f
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gosh> <span class="synSpecial">(</span><span class="synStatement">string=</span>? <span class="synConstant">"abc"</span> <span class="synConstant">"abc"</span><span class="synSpecial">)</span>
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#<span class="synStatement">t</span>
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gosh> <span class="synSpecial">(</span><span class="synStatement">string=</span>? <span class="synConstant">"abc"</span> <span class="synConstant">"ABC"</span><span class="synSpecial">)</span>
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#f
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</pre>
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<blockquote>
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<ul>
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<li>
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