92 lines
5.4 KiB
Markdown
92 lines
5.4 KiB
Markdown
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title: ソフト開発の過去問で出てきた再帰をGaucheで書く
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author: kazu634
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date: 2008-09-06
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url: /2008/09/06/_1098/
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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:4259;}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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- つれづれ
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---
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<div class="section">
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<p>
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ソフトウェア開発者試験ででてきた再帰を使った関数をGaucheで書いてみた。元の関数をCで書くとこんな感じになる:
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</p>
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<pre class="syntax-highlight">
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<span class="synComment">/* ======================= */</span>
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<span class="synComment">/* === Include library === */</span>
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<span class="synComment">/* ======================= */</span>
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<span class="synPreProc">#include </span><span class="synConstant"><stdio.h></span>
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<span class="synComment">/* ==================== */</span>
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<span class="synComment">/* === Main Routine === */</span>
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<span class="synComment">/* ==================== */</span>
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<span class="synType">void</span> prnt_digit(<span class="synType">int</span> n)
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{
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<span class="synStatement">if</span> (<span class="synConstant"></span> == n){
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<span class="synStatement">return</span>;
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}
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printf(<span class="synConstant">"</span><span class="synSpecial">%d</span><span class="synConstant">"</span>, n);
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prnt_digit(n - <span class="synConstant">1</span>);
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printf(<span class="synConstant">"</span><span class="synSpecial">%d</span><span class="synConstant">"</span>, n);
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}
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<span class="synType">int</span> main(<span class="synType">int</span> argc, <span class="synType">char</span> *argv[])
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{
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prnt_digit(<span class="synConstant">5</span>);
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printf(<span class="synConstant">"</span><span class="synSpecial">\n</span><span class="synConstant">"</span>);
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<span class="synStatement">return</span> <span class="synConstant"></span>;
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}
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</pre>
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<p>
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これをgaucheで書いてみる:
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</p>
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<pre class="syntax-highlight">
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<span class="synComment">;; lambdaを使わないバージョン</span>
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<span class="synSpecial">(</span>define <span class="synSpecial">(</span>proc n<span class="synSpecial">)</span>
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<span class="synSpecial">(</span>define <span class="synSpecial">(</span>tmp_proc temp<span class="synSpecial">)</span>
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<span class="synSpecial">(</span><span class="synStatement">print</span> n<span class="synSpecial">)</span>
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<span class="synSpecial">(</span>proc <span class="synSpecial">(</span><span class="synStatement">-</span> n <span class="synConstant">1</span><span class="synSpecial">))</span>
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<span class="synSpecial">(</span><span class="synStatement">print</span> n<span class="synSpecial">))</span>
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<span class="synSpecial">(</span><span class="synStatement">if</span> <span class="synSpecial">(</span><span class="synStatement">=</span> n <span class="synConstant"></span><span class="synSpecial">)</span>
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n
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<span class="synSpecial">(</span>tmp_proc <span class="synSpecial">(</span><span class="synStatement">-</span> n <span class="synConstant">1</span><span class="synSpecial">))))</span>
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<span class="synComment">;; がんばってlambda使ってみたバージョン</span>
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<span class="synSpecial">(</span>define <span class="synSpecial">(</span>proc_1 n<span class="synSpecial">)</span>
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<span class="synSpecial">(</span><span class="synStatement">if</span> <span class="synSpecial">(</span><span class="synStatement">=</span> n <span class="synConstant"></span><span class="synSpecial">)</span>
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n
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<span class="synSpecial">((</span><span class="synStatement">lambda</span> <span class="synSpecial">(</span>temp<span class="synSpecial">)</span>
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<span class="synSpecial">(</span><span class="synStatement">print</span> n<span class="synSpecial">)</span>
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<span class="synSpecial">(</span>proc_1 <span class="synSpecial">(</span><span class="synStatement">-</span> n <span class="synConstant">1</span><span class="synSpecial">))</span>
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<span class="synSpecial">(</span><span class="synStatement">print</span> n<span class="synSpecial">))</span>
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<span class="synSpecial">(</span><span class="synStatement">-</span> n <span class="synConstant">1</span><span class="synSpecial">))))</span>
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</pre>
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<p>
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lambdaは手続きを返すんだから「(」を二重に重ねないと引数をlambdaの無名関数に渡すことができないわけですね。なるほど。
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</p>
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<p>
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追記:
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</p>
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<p>
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condは暗黙でbeginが省略されていると解釈される。ifはそうじゃない。だから今回の場合は
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</p>
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<pre class="syntax-highlight">
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<span class="synSpecial">(</span>define <span class="synSpecial">(</span>proc_2 n<span class="synSpecial">)</span>
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<span class="synSpecial">(</span><span class="synStatement">if</span> <span class="synSpecial">(</span><span class="synStatement">=</span> n <span class="synConstant"></span><span class="synSpecial">)</span>
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n
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<span class="synSpecial">(</span>begin
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<span class="synSpecial">(</span><span class="synStatement">print</span> n<span class="synSpecial">)</span>
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<span class="synSpecial">(</span>proc_1 <span class="synSpecial">(</span><span class="synStatement">-</span> n <span class="synConstant">1</span><span class="synSpecial">))</span>
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<span class="synSpecial">(</span><span class="synStatement">print</span> n<span class="synSpecial">))))</span>
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</pre>
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<p>
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こうでもいいわけか。
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</p>
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</div>
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