blog/content/post/2010-09-05-00001378.md

---
title: 'Lispの問題 from 「L-99: Ninety-Nine Lisp Problems」'
author: kazu634
date: 2010-09-05
url: /2010/09/05/_1562/
wordtwit_post_info:
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categories:
  - gauche
  - Lisp

---
<div class="section">
<p>
    またまた頑張ってみました。letrecを使って、結果を渡しながらやっている。もしかしたら、継続で書き換えられる？
</p>
  
<pre class="syntax-highlight">
<span class="synComment">;; P07 (**) Flatten a nested list structure.</span>
<span class="synComment">;;     Transform a list, possibly holding lists as elements into a `flat' list by replacing each list with its elements (recursively).</span>
<span class="synComment">;;     Example:</span>
<span class="synComment">;;     * (my-flatten '(a (b (c d) e)))</span>
<span class="synComment">;;     (A B C D E)</span>
<span class="synComment">;;     Hint: Use the predefined functions list and append.</span>
<span class="synSpecial">(</span>define <span class="synSpecial">(</span><span class="synStatement">atom</span>? l<span class="synSpecial">)</span>
<span class="synSpecial">(</span><span class="synStatement">and</span> <span class="synSpecial">(</span><span class="synStatement">not</span> <span class="synSpecial">(</span>pair? l<span class="synSpecial">))</span>
<span class="synSpecial">(</span><span class="synStatement">not</span> <span class="synSpecial">(</span><span class="synStatement">null</span>? l<span class="synSpecial">))))</span>
<span class="synSpecial">(</span>define <span class="synSpecial">(</span>my-flatten l<span class="synSpecial">)</span>
<span class="synSpecial">(</span>letrec <span class="synSpecial">((</span>temp <span class="synSpecial">(</span><span class="synStatement">lambda</span> <span class="synSpecial">(</span>result l<span class="synSpecial">)</span>
<span class="synSpecial">(</span><span class="synStatement">cond</span>
[<span class="synSpecial">(</span><span class="synStatement">null</span>? l<span class="synSpecial">)</span> result]
[<span class="synSpecial">(</span><span class="synStatement">atom</span>? <span class="synSpecial">(</span><span class="synStatement">car</span> l<span class="synSpecial">))</span> <span class="synSpecial">(</span>temp <span class="synSpecial">(</span><span class="synStatement">append</span> result
<span class="synSpecial">(</span><span class="synStatement">list</span> <span class="synSpecial">(</span><span class="synStatement">car</span> l<span class="synSpecial">)))</span>
<span class="synSpecial">(</span><span class="synStatement">cdr</span> l<span class="synSpecial">))</span>]
[else <span class="synSpecial">(</span>temp <span class="synSpecial">(</span>temp result <span class="synSpecial">(</span><span class="synStatement">car</span> l<span class="synSpecial">))</span>
<span class="synSpecial">(</span><span class="synStatement">cdr</span> l<span class="synSpecial">))</span>]<span class="synSpecial">))))</span>
<span class="synSpecial">(</span>temp <span class="synSpecial">'()</span> l<span class="synSpecial">)))</span>
<span class="synSpecial">(</span>my-flatten <span class="synSpecial">'(</span>a <span class="synSpecial">(</span>b <span class="synSpecial">(</span>c d<span class="synSpecial">)</span> e<span class="synSpecial">)))</span>
<span class="synComment">;; P08 (**) Eliminate consecutive duplicates of list elements.</span>
<span class="synComment">;;     If a list contains repeated elements they should be replaced with a single copy of the element. The order of the elements should not be changed.</span>
<span class="synComment">;;     Example:</span>
<span class="synComment">;;     * (compress '(a a a a b c c a a d e e e e))</span>
<span class="synComment">;;     (A B C A D E)</span>
<span class="synSpecial">(</span>define <span class="synSpecial">(</span>compress l<span class="synSpecial">)</span>
<span class="synSpecial">(</span>letrec <span class="synSpecial">((</span>temp <span class="synSpecial">(</span><span class="synStatement">lambda</span> <span class="synSpecial">(</span>front result l<span class="synSpecial">)</span>
<span class="synSpecial">(</span><span class="synStatement">cond</span>
[<span class="synSpecial">(</span><span class="synStatement">null</span>? l<span class="synSpecial">)</span> result]
[<span class="synSpecial">(</span><span class="synStatement">eq</span>? front <span class="synSpecial">(</span><span class="synStatement">car</span> l<span class="synSpecial">))</span> <span class="synSpecial">(</span>temp front
result
<span class="synSpecial">(</span><span class="synStatement">cdr</span> l<span class="synSpecial">))</span>]
[else <span class="synSpecial">(</span>temp <span class="synSpecial">(</span><span class="synStatement">car</span> l<span class="synSpecial">)</span>
<span class="synSpecial">(</span><span class="synStatement">append</span> result <span class="synSpecial">(</span><span class="synStatement">list</span> <span class="synSpecial">(</span><span class="synStatement">car</span> l<span class="synSpecial">)))</span>
<span class="synSpecial">(</span><span class="synStatement">cdr</span> l<span class="synSpecial">))</span>]<span class="synSpecial">))))</span>
<span class="synSpecial">(</span>temp <span class="synSpecial">'()</span> <span class="synSpecial">'()</span> l<span class="synSpecial">)))</span>
<span class="synSpecial">(</span>compress <span class="synSpecial">'(</span>a a a a b c c a a d e e e e<span class="synSpecial">))</span>
</pre>
</div>