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<title>src/Servant/Server/Internal/Context.hs</title>
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<pre><a name="line-1"></a><span class='hs-comment'>{-# LANGUAGE CPP                        #-}</span>
<a name="line-2"></a><span class='hs-comment'>{-# LANGUAGE DataKinds                  #-}</span>
<a name="line-3"></a><span class='hs-comment'>{-# LANGUAGE FlexibleContexts           #-}</span>
<a name="line-4"></a><span class='hs-comment'>{-# LANGUAGE FlexibleInstances          #-}</span>
<a name="line-5"></a><span class='hs-comment'>{-# LANGUAGE GADTs                      #-}</span>
<a name="line-6"></a><span class='hs-comment'>{-# LANGUAGE KindSignatures             #-}</span>
<a name="line-7"></a><span class='hs-comment'>{-# LANGUAGE MultiParamTypeClasses      #-}</span>
<a name="line-8"></a><span class='hs-comment'>{-# LANGUAGE ScopedTypeVariables        #-}</span>
<a name="line-9"></a><span class='hs-comment'>{-# LANGUAGE TypeOperators              #-}</span>
<a name="line-10"></a>
<a name="line-11"></a><span class='hs-cpp'>#include "overlapping-compat.h"</span>
<a name="line-12"></a>
<a name="line-13"></a><span class='hs-keyword'>module</span> <span class='hs-conid'>Servant</span><span class='hs-varop'>.</span><span class='hs-conid'>Server</span><span class='hs-varop'>.</span><span class='hs-conid'>Internal</span><span class='hs-varop'>.</span><span class='hs-conid'>Context</span> <span class='hs-keyword'>where</span>
<a name="line-14"></a>
<a name="line-15"></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-16"></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-17"></a>
<a name="line-18"></a><a name="Context"></a><span class='hs-comment'>-- | 'Context's are used to pass values to combinators. (They are __not__ meant</span>
<a name="line-19"></a><a name="Context"></a><span class='hs-comment'>-- to be used to pass parameters to your handlers, i.e. they should not replace</span>
<a name="line-20"></a><a name="Context"></a><span class='hs-comment'>-- any custom 'Control.Monad.Trans.Reader.ReaderT'-monad-stack that you're using</span>
<a name="line-21"></a><a name="Context"></a><span class='hs-comment'>-- with 'Servant.Utils.Enter'.) If you don't use combinators that</span>
<a name="line-22"></a><a name="Context"></a><span class='hs-comment'>-- require any context entries, you can just use 'Servant.Server.serve' as always.</span>
<a name="line-23"></a><a name="Context"></a><span class='hs-comment'>--</span>
<a name="line-24"></a><a name="Context"></a><span class='hs-comment'>-- If you are using combinators that require a non-empty 'Context' you have to</span>
<a name="line-25"></a><a name="Context"></a><span class='hs-comment'>-- use 'Servant.Server.serveWithContext' and pass it a 'Context' that contains all</span>
<a name="line-26"></a><a name="Context"></a><span class='hs-comment'>-- the values your combinators need. A 'Context' is essentially a heterogenous</span>
<a name="line-27"></a><a name="Context"></a><span class='hs-comment'>-- list and accessing the elements is being done by type (see 'getContextEntry').</span>
<a name="line-28"></a><a name="Context"></a><span class='hs-comment'>-- The parameter of the type 'Context' is a type-level list reflecting the types</span>
<a name="line-29"></a><a name="Context"></a><span class='hs-comment'>-- of the contained context entries. To create a 'Context' with entries, use the</span>
<a name="line-30"></a><a name="Context"></a><span class='hs-comment'>-- operator @(':.')@:</span>
<a name="line-31"></a><a name="Context"></a><span class='hs-comment'>--</span>
<a name="line-32"></a><a name="Context"></a><span class='hs-comment'>-- &gt;&gt;&gt; :type True :. () :. EmptyContext</span>
<a name="line-33"></a><a name="Context"></a><span class='hs-comment'>-- True :. () :. EmptyContext :: Context '[Bool, ()]</span>
<a name="line-34"></a><a name="Context"></a><span class='hs-keyword'>data</span> <span class='hs-conid'>Context</span> <span class='hs-varid'>contextTypes</span> <span class='hs-keyword'>where</span>
<a name="line-35"></a>    <span class='hs-conid'>EmptyContext</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Context</span> <span class='hs-chr'>'</span><span class='hs-conid'>[]</span>
<a name="line-36"></a>    <span class='hs-layout'>(</span><span class='hs-conop'>:.</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>::</span> <span class='hs-varid'>x</span> <span class='hs-keyglyph'>-&gt;</span> <span class='hs-conid'>Context</span> <span class='hs-varid'>xs</span> <span class='hs-keyglyph'>-&gt;</span> <span class='hs-conid'>Context</span> <span class='hs-layout'>(</span><span class='hs-varid'>x</span> <span class='hs-chr'>'</span><span class='hs-conop'>:</span> <span class='hs-varid'>xs</span><span class='hs-layout'>)</span>
<a name="line-37"></a><span class='hs-keyword'>infixr</span> <span class='hs-num'>5</span> <span class='hs-conop'>:.</span>
<a name="line-38"></a>
<a name="line-39"></a><a name="instance%20Show%20(Context%20'%5b%5d)"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Show</span> <span class='hs-layout'>(</span><span class='hs-conid'>Context</span> <span class='hs-chr'>'</span><span class='hs-conid'>[]</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-40"></a>  <span class='hs-varid'>show</span> <span class='hs-conid'>EmptyContext</span> <span class='hs-keyglyph'>=</span> <span class='hs-str'>"EmptyContext"</span>
<a name="line-41"></a><a name="instance%20(Show%20a,%20Show%20(Context"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>Show</span> <span class='hs-varid'>a</span><span class='hs-layout'>,</span> <span class='hs-conid'>Show</span> <span class='hs-layout'>(</span><span class='hs-conid'>Context</span> <span class='hs-keyword'>as</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=&gt;</span> <span class='hs-conid'>Show</span> <span class='hs-layout'>(</span><span class='hs-conid'>Context</span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span> <span class='hs-chr'>'</span><span class='hs-conop'>:</span> <span class='hs-keyword'>as</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-42"></a>  <span class='hs-varid'>showsPrec</span> <span class='hs-varid'>outerPrecedence</span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span> <span class='hs-conop'>:.</span> <span class='hs-keyword'>as</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span>
<a name="line-43"></a>    <span class='hs-varid'>showParen</span> <span class='hs-layout'>(</span><span class='hs-varid'>outerPrecedence</span> <span class='hs-varop'>&gt;</span> <span class='hs-num'>5</span><span class='hs-layout'>)</span> <span class='hs-varop'>$</span>
<a name="line-44"></a>      <span class='hs-varid'>shows</span> <span class='hs-varid'>a</span> <span class='hs-varop'>.</span> <span class='hs-varid'>showString</span> <span class='hs-str'>" :. "</span> <span class='hs-varop'>.</span> <span class='hs-varid'>shows</span> <span class='hs-keyword'>as</span>
<a name="line-45"></a>
<a name="line-46"></a><a name="instance%20Eq%20(Context%20'%5b%5d)"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Eq</span> <span class='hs-layout'>(</span><span class='hs-conid'>Context</span> <span class='hs-chr'>'</span><span class='hs-conid'>[]</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-47"></a>    <span class='hs-keyword'>_</span> <span class='hs-varop'>==</span> <span class='hs-keyword'>_</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>True</span>
<a name="line-48"></a><a name="instance%20(Eq%20a,%20Eq%20(Context"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>Eq</span> <span class='hs-varid'>a</span><span class='hs-layout'>,</span> <span class='hs-conid'>Eq</span> <span class='hs-layout'>(</span><span class='hs-conid'>Context</span> <span class='hs-keyword'>as</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=&gt;</span> <span class='hs-conid'>Eq</span> <span class='hs-layout'>(</span><span class='hs-conid'>Context</span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span> <span class='hs-chr'>'</span><span class='hs-conop'>:</span> <span class='hs-keyword'>as</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-49"></a>    <span class='hs-varid'>x1</span> <span class='hs-conop'>:.</span> <span class='hs-varid'>y1</span> <span class='hs-varop'>==</span> <span class='hs-varid'>x2</span> <span class='hs-conop'>:.</span> <span class='hs-varid'>y2</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>x1</span> <span class='hs-varop'>==</span> <span class='hs-varid'>x2</span> <span class='hs-varop'>&amp;&amp;</span> <span class='hs-varid'>y1</span> <span class='hs-varop'>==</span> <span class='hs-varid'>y2</span>
<a name="line-50"></a>
<a name="line-51"></a><a name="HasContextEntry"></a><span class='hs-comment'>-- | This class is used to access context entries in 'Context's. 'getContextEntry'</span>
<a name="line-52"></a><a name="HasContextEntry"></a><span class='hs-comment'>-- returns the first value where the type matches:</span>
<a name="line-53"></a><a name="HasContextEntry"></a><span class='hs-comment'>--</span>
<a name="line-54"></a><a name="HasContextEntry"></a><span class='hs-comment'>-- &gt;&gt;&gt; getContextEntry (True :. False :. EmptyContext) :: Bool</span>
<a name="line-55"></a><a name="HasContextEntry"></a><span class='hs-comment'>-- True</span>
<a name="line-56"></a><a name="HasContextEntry"></a><span class='hs-comment'>--</span>
<a name="line-57"></a><a name="HasContextEntry"></a><span class='hs-comment'>-- If the 'Context' does not contain an entry of the requested type, you'll get</span>
<a name="line-58"></a><a name="HasContextEntry"></a><span class='hs-comment'>-- an error:</span>
<a name="line-59"></a><a name="HasContextEntry"></a><span class='hs-comment'>--</span>
<a name="line-60"></a><a name="HasContextEntry"></a><span class='hs-comment'>-- &gt;&gt;&gt; getContextEntry (True :. False :. EmptyContext) :: String</span>
<a name="line-61"></a><a name="HasContextEntry"></a><span class='hs-comment'>-- ...</span>
<a name="line-62"></a><a name="HasContextEntry"></a><span class='hs-comment'>-- ...No instance for (HasContextEntry '[] [Char])</span>
<a name="line-63"></a><a name="HasContextEntry"></a><span class='hs-comment'>-- ...</span>
<a name="line-64"></a><a name="HasContextEntry"></a><span class='hs-keyword'>class</span> <span class='hs-conid'>HasContextEntry</span> <span class='hs-layout'>(</span><span class='hs-varid'>context</span> <span class='hs-keyglyph'>::</span> <span class='hs-keyglyph'>[</span><span class='hs-varop'>*</span><span class='hs-keyglyph'>]</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-varid'>val</span> <span class='hs-keyglyph'>::</span> <span class='hs-varop'>*</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-65"></a>    <span class='hs-varid'>getContextEntry</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Context</span> <span class='hs-varid'>context</span> <span class='hs-keyglyph'>-&gt;</span> <span class='hs-varid'>val</span>
<a name="line-66"></a>
<a name="line-67"></a><a name="instance%20HasContextEntry%20(notIt%20':%20xs)%20val"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>OVERLAPPABLE_</span>
<a name="line-68"></a>         <span class='hs-conid'>HasContextEntry</span> <span class='hs-varid'>xs</span> <span class='hs-varid'>val</span> <span class='hs-keyglyph'>=&gt;</span> <span class='hs-conid'>HasContextEntry</span> <span class='hs-layout'>(</span><span class='hs-varid'>notIt</span> <span class='hs-chr'>'</span><span class='hs-conop'>:</span> <span class='hs-varid'>xs</span><span class='hs-layout'>)</span> <span class='hs-varid'>val</span> <span class='hs-keyword'>where</span>
<a name="line-69"></a>    <span class='hs-varid'>getContextEntry</span> <span class='hs-layout'>(</span><span class='hs-keyword'>_</span> <span class='hs-conop'>:.</span> <span class='hs-varid'>xs</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>getContextEntry</span> <span class='hs-varid'>xs</span>
<a name="line-70"></a>
<a name="line-71"></a><a name="instance%20OVERLAPPING_%20HasContextEntry%20(val%20':%20xs)%20val"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>OVERLAPPING_</span>
<a name="line-72"></a>         <span class='hs-conid'>HasContextEntry</span> <span class='hs-layout'>(</span><span class='hs-varid'>val</span> <span class='hs-chr'>'</span><span class='hs-conop'>:</span> <span class='hs-varid'>xs</span><span class='hs-layout'>)</span> <span class='hs-varid'>val</span> <span class='hs-keyword'>where</span>
<a name="line-73"></a>    <span class='hs-varid'>getContextEntry</span> <span class='hs-layout'>(</span><span class='hs-varid'>x</span> <span class='hs-conop'>:.</span> <span class='hs-keyword'>_</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>x</span>
<a name="line-74"></a>
<a name="line-75"></a><span class='hs-comment'>-- * support for named subcontexts</span>
<a name="line-76"></a>
<a name="line-77"></a><a name="NamedContext"></a><span class='hs-comment'>-- | Normally context entries are accessed by their types. In case you need</span>
<a name="line-78"></a><a name="NamedContext"></a><span class='hs-comment'>-- to have multiple values of the same type in your 'Context' and need to access</span>
<a name="line-79"></a><a name="NamedContext"></a><span class='hs-comment'>-- them, we provide 'NamedContext'. You can think of it as sub-namespaces for</span>
<a name="line-80"></a><a name="NamedContext"></a><span class='hs-comment'>-- 'Context's.</span>
<a name="line-81"></a><a name="NamedContext"></a><span class='hs-keyword'>data</span> <span class='hs-conid'>NamedContext</span> <span class='hs-layout'>(</span><span class='hs-varid'>name</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Symbol</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-varid'>subContext</span> <span class='hs-keyglyph'>::</span> <span class='hs-keyglyph'>[</span><span class='hs-varop'>*</span><span class='hs-keyglyph'>]</span><span class='hs-layout'>)</span>
<a name="line-82"></a>  <span class='hs-keyglyph'>=</span> <span class='hs-conid'>NamedContext</span> <span class='hs-layout'>(</span><span class='hs-conid'>Context</span> <span class='hs-varid'>subContext</span><span class='hs-layout'>)</span>
<a name="line-83"></a>
<a name="line-84"></a><a name="descendIntoNamedContext"></a><span class='hs-comment'>-- | 'descendIntoNamedContext' allows you to access `NamedContext's. Usually you</span>
<a name="line-85"></a><span class='hs-comment'>-- won't have to use it yourself but instead use a combinator like</span>
<a name="line-86"></a><span class='hs-comment'>-- 'Servant.API.WithNamedContext.WithNamedContext'.</span>
<a name="line-87"></a><span class='hs-comment'>--</span>
<a name="line-88"></a><span class='hs-comment'>-- This is how 'descendIntoNamedContext' works:</span>
<a name="line-89"></a><span class='hs-comment'>--</span>
<a name="line-90"></a><span class='hs-comment'>-- &gt;&gt;&gt; :set -XFlexibleContexts</span>
<a name="line-91"></a><span class='hs-comment'>-- &gt;&gt;&gt; let subContext = True :. EmptyContext</span>
<a name="line-92"></a><span class='hs-comment'>-- &gt;&gt;&gt; :type subContext</span>
<a name="line-93"></a><span class='hs-comment'>-- subContext :: Context '[Bool]</span>
<a name="line-94"></a><span class='hs-comment'>-- &gt;&gt;&gt; let parentContext = False :. (NamedContext subContext :: NamedContext "subContext" '[Bool]) :. EmptyContext</span>
<a name="line-95"></a><span class='hs-comment'>-- &gt;&gt;&gt; :type parentContext</span>
<a name="line-96"></a><span class='hs-comment'>-- parentContext :: Context '[Bool, NamedContext "subContext" '[Bool]]</span>
<a name="line-97"></a><span class='hs-comment'>-- &gt;&gt;&gt; descendIntoNamedContext (Proxy :: Proxy "subContext") parentContext :: Context '[Bool]</span>
<a name="line-98"></a><span class='hs-comment'>-- True :. EmptyContext</span>
<a name="line-99"></a><span class='hs-definition'>descendIntoNamedContext</span> <span class='hs-keyglyph'>::</span> <span class='hs-keyword'>forall</span> <span class='hs-varid'>context</span> <span class='hs-varid'>name</span> <span class='hs-varid'>subContext</span> <span class='hs-varop'>.</span>
<a name="line-100"></a>  <span class='hs-conid'>HasContextEntry</span> <span class='hs-varid'>context</span> <span class='hs-layout'>(</span><span class='hs-conid'>NamedContext</span> <span class='hs-varid'>name</span> <span class='hs-varid'>subContext</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=&gt;</span>
<a name="line-101"></a>  <span class='hs-conid'>Proxy</span> <span class='hs-layout'>(</span><span class='hs-varid'>name</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Symbol</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-&gt;</span> <span class='hs-conid'>Context</span> <span class='hs-varid'>context</span> <span class='hs-keyglyph'>-&gt;</span> <span class='hs-conid'>Context</span> <span class='hs-varid'>subContext</span>
<a name="line-102"></a><span class='hs-definition'>descendIntoNamedContext</span> <span class='hs-conid'>Proxy</span> <span class='hs-varid'>context</span> <span class='hs-keyglyph'>=</span>
<a name="line-103"></a>  <span class='hs-keyword'>let</span> <span class='hs-conid'>NamedContext</span> <span class='hs-varid'>subContext</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>getContextEntry</span> <span class='hs-varid'>context</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>NamedContext</span> <span class='hs-varid'>name</span> <span class='hs-varid'>subContext</span>
<a name="line-104"></a>  <span class='hs-keyword'>in</span> <span class='hs-varid'>subContext</span>
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