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<title>src/Servant/API/Capture.hs</title>
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<pre><a name="line-1"></a><span class='hs-comment'>{-# LANGUAGE PolyKinds #-}</span>
<a name="line-2"></a><span class='hs-comment'>{-# LANGUAGE TypeFamilies #-}</span>
<a name="line-3"></a><span class='hs-comment'>{-# LANGUAGE TypeOperators #-}</span>
<a name="line-4"></a><span class='hs-comment'>{-# LANGUAGE FlexibleContexts #-}</span>
<a name="line-5"></a><span class='hs-comment'>{-# LANGUAGE FlexibleInstances #-}</span>
<a name="line-6"></a><span class='hs-comment'>{-# LANGUAGE ScopedTypeVariables #-}</span>
<a name="line-7"></a><span class='hs-keyword'>module</span> <span class='hs-conid'>Servant</span><span class='hs-varop'>.</span><span class='hs-conid'>API</span><span class='hs-varop'>.</span><span class='hs-conid'>Capture</span> <span class='hs-layout'>(</span><span class='hs-conid'>Capture</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-8"></a>
<a name="line-9"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Proxy</span>
<a name="line-10"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Text</span>
<a name="line-11"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>GHC</span><span class='hs-varop'>.</span><span class='hs-conid'>TypeLits</span>
<a name="line-12"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Network</span><span class='hs-varop'>.</span><span class='hs-conid'>Wai</span>
<a name="line-13"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Servant</span><span class='hs-varop'>.</span><span class='hs-conid'>API</span><span class='hs-varop'>.</span><span class='hs-conid'>Sub</span>
<a name="line-14"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Servant</span><span class='hs-varop'>.</span><span class='hs-conid'>Common</span><span class='hs-varop'>.</span><span class='hs-conid'>Text</span>
<a name="line-15"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Servant</span><span class='hs-varop'>.</span><span class='hs-conid'>Server</span>
<a name="line-16"></a>
<a name="line-17"></a><span class='hs-comment'>-- | Capture a value from the request path under a certain type @a@.</span>
<a name="line-18"></a><span class='hs-comment'>--</span>
<a name="line-19"></a><span class='hs-comment'>-- Example:</span>
<a name="line-20"></a><span class='hs-comment'>--</span>
<a name="line-21"></a><span class='hs-comment'>-- > -- GET /books/:isbn</span>
<a name="line-22"></a><span class='hs-comment'>-- > type MyApi = "books" :> Capture "isbn" Text :> Get Book</span>
<a name="line-23"></a><span class='hs-keyword'>data</span> <span class='hs-conid'>Capture</span> <span class='hs-varid'>sym</span> <span class='hs-varid'>a</span>
<a name="line-24"></a>
<a name="line-25"></a><a name="captured"></a><span class='hs-definition'>captured</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>FromText</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=></span> <span class='hs-varid'>proxy</span> <span class='hs-layout'>(</span><span class='hs-conid'>Capture</span> <span class='hs-varid'>sym</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Text</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Maybe</span> <span class='hs-varid'>a</span>
<a name="line-26"></a><span class='hs-definition'>captured</span> <span class='hs-keyword'>_</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>fromText</span>
<a name="line-27"></a>
<a name="line-28"></a><a name="instance%20HasServer%20(Capture%20capture%20a%20:%3e%20sublayout)"></a><span class='hs-comment'>-- | If you use 'Capture' in one of the endpoints for your API,</span>
<a name="line-29"></a><a name="instance%20HasServer%20(Capture%20capture%20a%20:%3e%20sublayout)"></a><span class='hs-comment'>-- this automatically requires your server-side handler to be a function</span>
<a name="line-30"></a><a name="instance%20HasServer%20(Capture%20capture%20a%20:%3e%20sublayout)"></a><span class='hs-comment'>-- that takes an argument of the type specified by the 'Capture'.</span>
<a name="line-31"></a><a name="instance%20HasServer%20(Capture%20capture%20a%20:%3e%20sublayout)"></a><span class='hs-comment'>-- This lets servant worry about getting it from the URL and turning</span>
<a name="line-32"></a><a name="instance%20HasServer%20(Capture%20capture%20a%20:%3e%20sublayout)"></a><span class='hs-comment'>-- it into a value of the type you specify.</span>
<a name="line-33"></a><a name="instance%20HasServer%20(Capture%20capture%20a%20:%3e%20sublayout)"></a><span class='hs-comment'>--</span>
<a name="line-34"></a><a name="instance%20HasServer%20(Capture%20capture%20a%20:%3e%20sublayout)"></a><span class='hs-comment'>-- You can control how it'll be converted from 'Text' to your type</span>
<a name="line-35"></a><a name="instance%20HasServer%20(Capture%20capture%20a%20:%3e%20sublayout)"></a><span class='hs-comment'>-- by simply providing an instance of 'FromText' for your type.</span>
<a name="line-36"></a><a name="instance%20HasServer%20(Capture%20capture%20a%20:%3e%20sublayout)"></a><span class='hs-comment'>--</span>
<a name="line-37"></a><a name="instance%20HasServer%20(Capture%20capture%20a%20:%3e%20sublayout)"></a><span class='hs-comment'>-- Example:</span>
<a name="line-38"></a><a name="instance%20HasServer%20(Capture%20capture%20a%20:%3e%20sublayout)"></a><span class='hs-comment'>--</span>
<a name="line-39"></a><a name="instance%20HasServer%20(Capture%20capture%20a%20:%3e%20sublayout)"></a><span class='hs-comment'>-- > type MyApi = "books" :> Capture "isbn" Text :> Get Book</span>
<a name="line-40"></a><a name="instance%20HasServer%20(Capture%20capture%20a%20:%3e%20sublayout)"></a><span class='hs-comment'>-- ></span>
<a name="line-41"></a><a name="instance%20HasServer%20(Capture%20capture%20a%20:%3e%20sublayout)"></a><span class='hs-comment'>-- > server :: Server MyApi</span>
<a name="line-42"></a><a name="instance%20HasServer%20(Capture%20capture%20a%20:%3e%20sublayout)"></a><span class='hs-comment'>-- > server = getBook</span>
<a name="line-43"></a><a name="instance%20HasServer%20(Capture%20capture%20a%20:%3e%20sublayout)"></a><span class='hs-comment'>-- > where getBook :: Text -> EitherT (Int, String) IO Book</span>
<a name="line-44"></a><a name="instance%20HasServer%20(Capture%20capture%20a%20:%3e%20sublayout)"></a><span class='hs-comment'>-- > getBook isbn = ...</span>
<a name="line-45"></a><a name="instance%20HasServer%20(Capture%20capture%20a%20:%3e%20sublayout)"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>KnownSymbol</span> <span class='hs-varid'>capture</span><span class='hs-layout'>,</span> <span class='hs-conid'>FromText</span> <span class='hs-varid'>a</span><span class='hs-layout'>,</span> <span class='hs-conid'>HasServer</span> <span class='hs-varid'>sublayout</span><span class='hs-layout'>)</span>
<a name="line-46"></a> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>HasServer</span> <span class='hs-layout'>(</span><span class='hs-conid'>Capture</span> <span class='hs-varid'>capture</span> <span class='hs-varid'>a</span> <span class='hs-conop'>:></span> <span class='hs-varid'>sublayout</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-47"></a>
<a name="line-48"></a> <span class='hs-keyword'>type</span> <span class='hs-conid'>Server</span> <span class='hs-layout'>(</span><span class='hs-conid'>Capture</span> <span class='hs-varid'>capture</span> <span class='hs-varid'>a</span> <span class='hs-conop'>:></span> <span class='hs-varid'>sublayout</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span>
<a name="line-49"></a> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Server</span> <span class='hs-varid'>sublayout</span>
<a name="line-50"></a>
<a name="line-51"></a> <span class='hs-varid'>route</span> <span class='hs-conid'>Proxy</span> <span class='hs-varid'>subserver</span> <span class='hs-varid'>request</span> <span class='hs-varid'>respond</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>case</span> <span class='hs-varid'>pathInfo</span> <span class='hs-varid'>request</span> <span class='hs-keyword'>of</span>
<a name="line-52"></a> <span class='hs-layout'>(</span><span class='hs-varid'>first</span> <span class='hs-conop'>:</span> <span class='hs-varid'>rest</span><span class='hs-layout'>)</span>
<a name="line-53"></a> <span class='hs-keyglyph'>-></span> <span class='hs-keyword'>case</span> <span class='hs-varid'>captured</span> <span class='hs-varid'>captureProxy</span> <span class='hs-varid'>first</span> <span class='hs-keyword'>of</span>
<a name="line-54"></a> <span class='hs-conid'>Nothing</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>respond</span> <span class='hs-varop'>$</span> <span class='hs-varid'>failWith</span> <span class='hs-conid'>NotFound</span>
<a name="line-55"></a> <span class='hs-conid'>Just</span> <span class='hs-varid'>v</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>route</span> <span class='hs-layout'>(</span><span class='hs-conid'>Proxy</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Proxy</span> <span class='hs-varid'>sublayout</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-varid'>subserver</span> <span class='hs-varid'>v</span><span class='hs-layout'>)</span> <span class='hs-varid'>request</span><span class='hs-layout'>{</span>
<a name="line-56"></a> <span class='hs-varid'>pathInfo</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>rest</span>
<a name="line-57"></a> <span class='hs-layout'>}</span> <span class='hs-varid'>respond</span>
<a name="line-58"></a> <span class='hs-keyword'>_</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>respond</span> <span class='hs-varop'>$</span> <span class='hs-varid'>failWith</span> <span class='hs-conid'>NotFound</span>
<a name="line-59"></a>
<a name="line-60"></a> <span class='hs-keyword'>where</span> <span class='hs-varid'>captureProxy</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Proxy</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Proxy</span> <span class='hs-layout'>(</span><span class='hs-conid'>Capture</span> <span class='hs-varid'>capture</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span>
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