blog/content/post/2011/05/30/2011-05-30-00001497.md

---
title: マクロを使って HTTP 接続を行う構文を作ってみた
author: kazu634
date: 2011-05-30
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categories:
  - gauche
  - Lisp

---
<div class="section">
<p>
    マクロを使って HTTP 接続を行う構文を作ってみようと決意したのですが、うまくできず。。。なぜだろう？？？
</p>

<h4>
    やってみたいこと
</h4>

<p>
    こういうパターンが良く出てきました:
</p>

<pre class="syntax-highlight">
<span class="synSpecial">(</span>receive <span class="synSpecial">(</span>status header body<span class="synSpecial">)</span>
<span class="synSpecial">(</span>http-get ...<span class="synSpecial">)</span>
<span class="synSpecial">(</span><span class="synStatement">cond</span>
[<span class="synSpecial">(</span><span class="synStatement">equal</span>? <span class="synConstant">&#34;200&#34;</span> status<span class="synSpecial">)</span> <span class="synSpecial">(</span>proc body<span class="synSpecial">)</span>] <span class="synComment">;; ここの手続きは指定したいなぁ</span>
[<span class="synSpecial">(</span><span class="synStatement">equal</span>? <span class="synConstant">&#34;400&#34;</span> status<span class="synSpecial">)</span> <span class="synSpecial">(</span><span class="synStatement">print</span> <span class="synConstant">&#34;Authentication failure.&#34;</span><span class="synSpecial">)</span>]
[else <span class="synSpecial">(</span><span class="synStatement">print</span> status header body<span class="synSpecial">)</span>]<span class="synSpecial">))</span>
</pre>

<p>
    こういうパターンをこんなように書けたらいいかなぁと思いました:
</p>

<pre class="syntax-highlight">
<span class="synSpecial">(</span>wrap-http <span class="synSpecial">(</span>http-get ...<span class="synSpecial">)</span> proc <span class="synSpecial">'((</span><span class="synConstant">&#34;400&#34;</span> . <span class="synConstant">&#34;Authentication failure.&#34;</span><span class="synSpecial">)))</span>
</pre>

<h4>
    とりあえず書いてみた
</h4>

<p>
    こんなのを書いてみました:
</p>

<pre class="syntax-highlight">
<span class="synSpecial">(</span>define-macro <span class="synSpecial">(</span>wrap-http http-method proc status-msg<span class="synSpecial">)</span>
<span class="synSpecial">(</span><span class="synStatement">let*</span> <span class="synSpecial">((</span>success <span class="synPreProc">`(</span><span class="synSpecial">(</span><span class="synStatement">equal</span>? <span class="synConstant">&#34;200&#34;</span> status<span class="synSpecial">)</span> <span class="synSpecial">(</span>,proc body<span class="synSpecial">)</span><span class="synPreProc">)</span><span class="synSpecial">)</span>
<span class="synSpecial">(</span>else-msg <span class="synPreProc">`(</span>else <span class="synSpecial">(</span><span class="synStatement">print</span> status header body<span class="synSpecial">)</span><span class="synPreProc">)</span><span class="synSpecial">))</span>
<span class="synPreProc">`(</span>receive <span class="synSpecial">(</span>status header body<span class="synSpecial">)</span>
,http-method
<span class="synSpecial">(</span><span class="synStatement">cond</span>
,success
,@<span class="synSpecial">(</span><span class="synStatement">map</span> <span class="synSpecial">(</span><span class="synStatement">lambda</span> <span class="synSpecial">(</span>s<span class="synSpecial">)</span>
<span class="synPreProc">`(</span><span class="synSpecial">(</span><span class="synStatement">equal</span>? ,<span class="synSpecial">(</span><span class="synStatement">car</span> s<span class="synSpecial">))</span> <span class="synSpecial">(</span><span class="synStatement">print</span> ,<span class="synSpecial">(</span><span class="synStatement">cdr</span> s<span class="synSpecial">))</span><span class="synPreProc">)</span><span class="synSpecial">)</span>
status-msg<span class="synSpecial">)</span>
,else-msg<span class="synSpecial">)</span><span class="synPreProc">)</span><span class="synSpecial">))</span>
</pre>

<p>
    でもこれを使おうとすると、「*** ERROR: Compile Error: pair required, but got quote」となってしまいました。。。なぜなのでしょう。。。
</p>

<h4>
    ちなみに
</h4>

<p>
    これは無事に実行出来るようなんだよなぁ:
</p>

<pre class="syntax-highlight">
gosh&#62; <span class="synSpecial">(</span><span class="synStatement">map</span> <span class="synSpecial">(</span><span class="synStatement">lambda</span> <span class="synSpecial">(</span>i<span class="synSpecial">)</span>
<span class="synPreProc">`(</span><span class="synSpecial">(</span><span class="synStatement">equal</span>? ,<span class="synSpecial">(</span><span class="synStatement">car</span> i<span class="synSpecial">))</span> <span class="synSpecial">(</span><span class="synStatement">print</span> ,<span class="synSpecial">(</span><span class="synStatement">cdr</span> i<span class="synSpecial">))</span><span class="synPreProc">)</span><span class="synSpecial">)</span>
<span class="synSpecial">'((</span><span class="synConstant">&#34;404&#34;</span> . <span class="synConstant">&#34;Not found&#34;</span><span class="synSpecial">)))</span>
<span class="synSpecial">(((</span><span class="synStatement">equal</span>? <span class="synConstant">&#34;404&#34;</span><span class="synSpecial">)</span> <span class="synSpecial">(</span><span class="synStatement">print</span> <span class="synConstant">&#34;Not found&#34;</span><span class="synSpecial">)))</span>
</pre>
</div>