Built from e0097e1

Author: alpmestan

posts/2018-07-12-servant-dsl-typelevel.html

@@ -273,7 +273,7 @@ <h1>A first modular attempt</h1>
 <a class="sourceLine" id="cb14-19" data-line-number="19">  <span class="co">-- we see that our little `LinkType` trick there allows</span></a>
 <a class="sourceLine" id="cb14-20" data-line-number="20">  <span class="co">-- link to receive arguments when appropriate</span></a>
 <a class="sourceLine" id="cb14-21" data-line-number="21">  link (<span class="dt">Capture</span> <span class="fu">:&gt;</span> api) captureValue <span class="fu">=</span> captureValue <span class="fu">:</span> link api</a></code></pre></div>
-<p>Looks good. Except that this does not typecheck. The problem is with the <code>Capture :&gt; api</code> and <code>Static :&gt; api</code> instances. While we know that the <code>link</code> function will eventually return a <code>Link</code>, once given arguments for all the <code>Capture</code>s, we don’t know whether there is another <code>Capture</code> later in <code>api</code>. If there is, then <code>link api</code> would have type e.g <code>String -&gt; Link</code>, and we cannot cons a <code>String</code> on top of… function.</p>
+<p>Looks good. Except that this does not typecheck. The problem is with the <code>Capture :&gt; api</code> and <code>Static :&gt; api</code> instances. While we know that the <code>link</code> function will eventually return a <code>Link</code>, once given arguments for all the <code>Capture</code>s, we don’t know whether there is another <code>Capture</code> later in <code>api</code>. If there is, then <code>link api</code> would have type e.g <code>String -&gt; Link</code>, and we cannot cons a <code>String</code> on top of… a function.</p>
 <p>We have to be a little smarter and accumulate the path components as we go without building up the final list directly. We will be accumulating the path components in reverse order, to make the accumulation efficient, and reverse the whole list at the end to give the final <code>Link</code> (<code>= [String]</code>) value.</p>
 <div class="sourceCode" id="cb15"><pre class="sourceCode haskell"><code class="sourceCode haskell"><a class="sourceLine" id="cb15-1" data-line-number="1"><span class="ot">link ::</span> <span class="dt">HasLink</span> endpoint <span class="ot">=&gt;</span> endpoint <span class="ot">-&gt;</span> <span class="dt">LinkType</span> endpoint</a>
 <a class="sourceLine" id="cb15-2" data-line-number="2">link e <span class="fu">=</span> link' e []</a>

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@@ -259,7 +259,7 @@
 <a class="sourceLine" id="cb14-19" data-line-number="19">  <span class="co">-- we see that our little `LinkType` trick there allows</span></a>
 <a class="sourceLine" id="cb14-20" data-line-number="20">  <span class="co">-- link to receive arguments when appropriate</span></a>
 <a class="sourceLine" id="cb14-21" data-line-number="21">  link (<span class="dt">Capture</span> <span class="fu">:&gt;</span> api) captureValue <span class="fu">=</span> captureValue <span class="fu">:</span> link api</a></code></pre></div>
-<p>Looks good. Except that this does not typecheck. The problem is with the <code>Capture :&gt; api</code> and <code>Static :&gt; api</code> instances. While we know that the <code>link</code> function will eventually return a <code>Link</code>, once given arguments for all the <code>Capture</code>s, we don’t know whether there is another <code>Capture</code> later in <code>api</code>. If there is, then <code>link api</code> would have type e.g <code>String -&gt; Link</code>, and we cannot cons a <code>String</code> on top of… function.</p>
+<p>Looks good. Except that this does not typecheck. The problem is with the <code>Capture :&gt; api</code> and <code>Static :&gt; api</code> instances. While we know that the <code>link</code> function will eventually return a <code>Link</code>, once given arguments for all the <code>Capture</code>s, we don’t know whether there is another <code>Capture</code> later in <code>api</code>. If there is, then <code>link api</code> would have type e.g <code>String -&gt; Link</code>, and we cannot cons a <code>String</code> on top of… a function.</p>
 <p>We have to be a little smarter and accumulate the path components as we go without building up the final list directly. We will be accumulating the path components in reverse order, to make the accumulation efficient, and reverse the whole list at the end to give the final <code>Link</code> (<code>= [String]</code>) value.</p>
 <div class="sourceCode" id="cb15"><pre class="sourceCode haskell"><code class="sourceCode haskell"><a class="sourceLine" id="cb15-1" data-line-number="1"><span class="ot">link ::</span> <span class="dt">HasLink</span> endpoint <span class="ot">=&gt;</span> endpoint <span class="ot">-&gt;</span> <span class="dt">LinkType</span> endpoint</a>
 <a class="sourceLine" id="cb15-2" data-line-number="2">link e <span class="fu">=</span> link&#39; e []</a>