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<title>src/Servant/Server/Internal/Router.hs</title>
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<pre><a name="line-1"></a><span class='hs-comment'>{-# LANGUAGE DeriveFunctor #-}</span>
<a name="line-2"></a><span class='hs-comment'>{-# LANGUAGE CPP #-}</span>
<a name="line-3"></a><span class='hs-comment'>{-# LANGUAGE GADTs #-}</span>
<a name="line-4"></a><span class='hs-comment'>{-# LANGUAGE KindSignatures #-}</span>
<a name="line-5"></a><span class='hs-comment'>{-# LANGUAGE OverloadedStrings #-}</span>
<a name="line-6"></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'>Router</span> <span class='hs-keyword'>where</span>
<a name="line-7"></a>
<a name="line-8"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Map</span> <span class='hs-layout'>(</span><span class='hs-conid'>Map</span><span class='hs-layout'>)</span>
<a name="line-9"></a><span class='hs-keyword'>import</span> <span class='hs-keyword'>qualified</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Map</span> <span class='hs-keyword'>as</span> <span class='hs-conid'>M</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'>Monoid</span>
<a name="line-11"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Text</span> <span class='hs-layout'>(</span><span class='hs-conid'>Text</span><span class='hs-layout'>)</span>
<a name="line-12"></a><span class='hs-keyword'>import</span> <span class='hs-keyword'>qualified</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Text</span> <span class='hs-keyword'>as</span> <span class='hs-conid'>T</span>
<a name="line-13"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Network</span><span class='hs-varop'>.</span><span class='hs-conid'>Wai</span> <span class='hs-layout'>(</span><span class='hs-conid'>Response</span><span class='hs-layout'>,</span> <span class='hs-varid'>pathInfo</span><span class='hs-layout'>)</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'>Server</span><span class='hs-varop'>.</span><span class='hs-conid'>Internal</span><span class='hs-varop'>.</span><span class='hs-conid'>RoutingApplication</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><span class='hs-varop'>.</span><span class='hs-conid'>Internal</span><span class='hs-varop'>.</span><span class='hs-conid'>ServantErr</span>
<a name="line-16"></a>
<a name="line-17"></a><a name="Router"></a><span class='hs-keyword'>type</span> <span class='hs-conid'>Router</span> <span class='hs-varid'>env</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Router'</span> <span class='hs-varid'>env</span> <span class='hs-conid'>RoutingApplication</span>
<a name="line-18"></a>
<a name="line-19"></a><a name="Router'"></a><span class='hs-comment'>-- | Internal representation of a router.</span>
<a name="line-20"></a><a name="Router'"></a><span class='hs-comment'>--</span>
<a name="line-21"></a><a name="Router'"></a><span class='hs-comment'>-- The first argument describes an environment type that is</span>
<a name="line-22"></a><a name="Router'"></a><span class='hs-comment'>-- expected as extra input by the routers at the leaves. The</span>
<a name="line-23"></a><a name="Router'"></a><span class='hs-comment'>-- environment is filled while running the router, with path</span>
<a name="line-24"></a><a name="Router'"></a><span class='hs-comment'>-- components that can be used to process captures.</span>
<a name="line-25"></a><a name="Router'"></a><span class='hs-comment'>--</span>
<a name="line-26"></a><a name="Router'"></a><span class='hs-keyword'>data</span> <span class='hs-conid'>Router'</span> <span class='hs-varid'>env</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=</span>
<a name="line-27"></a> <span class='hs-conid'>StaticRouter</span> <span class='hs-layout'>(</span><span class='hs-conid'>Map</span> <span class='hs-conid'>Text</span> <span class='hs-layout'>(</span><span class='hs-conid'>Router'</span> <span class='hs-varid'>env</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>[</span><span class='hs-varid'>env</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a</span><span class='hs-keyglyph'>]</span>
<a name="line-28"></a> <span class='hs-comment'>-- ^ the map contains routers for subpaths (first path component used</span>
<a name="line-29"></a> <span class='hs-comment'>-- for lookup and removed afterwards), the list contains handlers</span>
<a name="line-30"></a> <span class='hs-comment'>-- for the empty path, to be tried in order</span>
<a name="line-31"></a> <span class='hs-keyglyph'>|</span> <span class='hs-conid'>CaptureRouter</span> <span class='hs-layout'>(</span><span class='hs-conid'>Router'</span> <span class='hs-layout'>(</span><span class='hs-conid'>Text</span><span class='hs-layout'>,</span> <span class='hs-varid'>env</span><span class='hs-layout'>)</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span>
<a name="line-32"></a> <span class='hs-comment'>-- ^ first path component is passed to the child router in its</span>
<a name="line-33"></a> <span class='hs-comment'>-- environment and removed afterwards</span>
<a name="line-34"></a> <span class='hs-keyglyph'>|</span> <span class='hs-conid'>CaptureAllRouter</span> <span class='hs-layout'>(</span><span class='hs-conid'>Router'</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-layout'>,</span> <span class='hs-varid'>env</span><span class='hs-layout'>)</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span>
<a name="line-35"></a> <span class='hs-comment'>-- ^ all path components are passed to the child router in its</span>
<a name="line-36"></a> <span class='hs-comment'>-- environment and are removed afterwards</span>
<a name="line-37"></a> <span class='hs-keyglyph'>|</span> <span class='hs-conid'>RawRouter</span> <span class='hs-layout'>(</span><span class='hs-varid'>env</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span>
<a name="line-38"></a> <span class='hs-comment'>-- ^ to be used for routes we do not know anything about</span>
<a name="line-39"></a> <span class='hs-keyglyph'>|</span> <span class='hs-conid'>Choice</span> <span class='hs-layout'>(</span><span class='hs-conid'>Router'</span> <span class='hs-varid'>env</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-conid'>Router'</span> <span class='hs-varid'>env</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span>
<a name="line-40"></a> <span class='hs-comment'>-- ^ left-biased choice between two routers</span>
<a name="line-41"></a> <span class='hs-keyword'>deriving</span> <span class='hs-conid'>Functor</span>
<a name="line-42"></a>
<a name="line-43"></a><a name="pathRouter"></a><span class='hs-comment'>-- | Smart constructor for a single static path component.</span>
<a name="line-44"></a><span class='hs-definition'>pathRouter</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Text</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Router'</span> <span class='hs-varid'>env</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Router'</span> <span class='hs-varid'>env</span> <span class='hs-varid'>a</span>
<a name="line-45"></a><span class='hs-definition'>pathRouter</span> <span class='hs-varid'>t</span> <span class='hs-varid'>r</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>StaticRouter</span> <span class='hs-layout'>(</span><span class='hs-conid'>M</span><span class='hs-varop'>.</span><span class='hs-varid'>singleton</span> <span class='hs-varid'>t</span> <span class='hs-varid'>r</span><span class='hs-layout'>)</span> <span class='hs-conid'>[]</span>
<a name="line-46"></a>
<a name="line-47"></a><a name="leafRouter"></a><span class='hs-comment'>-- | Smart constructor for a leaf, i.e., a router that expects</span>
<a name="line-48"></a><span class='hs-comment'>-- the empty path.</span>
<a name="line-49"></a><span class='hs-comment'>--</span>
<a name="line-50"></a><span class='hs-definition'>leafRouter</span> <span class='hs-keyglyph'>::</span> <span class='hs-layout'>(</span><span class='hs-varid'>env</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Router'</span> <span class='hs-varid'>env</span> <span class='hs-varid'>a</span>
<a name="line-51"></a><span class='hs-definition'>leafRouter</span> <span class='hs-varid'>l</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>StaticRouter</span> <span class='hs-conid'>M</span><span class='hs-varop'>.</span><span class='hs-varid'>empty</span> <span class='hs-keyglyph'>[</span><span class='hs-varid'>l</span><span class='hs-keyglyph'>]</span>
<a name="line-52"></a>
<a name="line-53"></a><a name="choice"></a><span class='hs-comment'>-- | Smart constructor for the choice between routers.</span>
<a name="line-54"></a><span class='hs-comment'>-- We currently optimize the following cases:</span>
<a name="line-55"></a><span class='hs-comment'>--</span>
<a name="line-56"></a><span class='hs-comment'>-- * Two static routers can be joined by joining their maps</span>
<a name="line-57"></a><span class='hs-comment'>-- and concatenating their leaf-lists.</span>
<a name="line-58"></a><span class='hs-comment'>-- * Two dynamic routers can be joined by joining their codomains.</span>
<a name="line-59"></a><span class='hs-comment'>-- * Choice nodes can be reordered.</span>
<a name="line-60"></a><span class='hs-comment'>--</span>
<a name="line-61"></a><span class='hs-definition'>choice</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Router'</span> <span class='hs-varid'>env</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Router'</span> <span class='hs-varid'>env</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Router'</span> <span class='hs-varid'>env</span> <span class='hs-varid'>a</span>
<a name="line-62"></a><span class='hs-definition'>choice</span> <span class='hs-layout'>(</span><span class='hs-conid'>StaticRouter</span> <span class='hs-varid'>table1</span> <span class='hs-varid'>ls1</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-conid'>StaticRouter</span> <span class='hs-varid'>table2</span> <span class='hs-varid'>ls2</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span>
<a name="line-63"></a> <span class='hs-conid'>StaticRouter</span> <span class='hs-layout'>(</span><span class='hs-conid'>M</span><span class='hs-varop'>.</span><span class='hs-varid'>unionWith</span> <span class='hs-varid'>choice</span> <span class='hs-varid'>table1</span> <span class='hs-varid'>table2</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-varid'>ls1</span> <span class='hs-varop'>++</span> <span class='hs-varid'>ls2</span><span class='hs-layout'>)</span>
<a name="line-64"></a><span class='hs-definition'>choice</span> <span class='hs-layout'>(</span><span class='hs-conid'>CaptureRouter</span> <span class='hs-varid'>router1</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-conid'>CaptureRouter</span> <span class='hs-varid'>router2</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span>
<a name="line-65"></a> <span class='hs-conid'>CaptureRouter</span> <span class='hs-layout'>(</span><span class='hs-varid'>choice</span> <span class='hs-varid'>router1</span> <span class='hs-varid'>router2</span><span class='hs-layout'>)</span>
<a name="line-66"></a><span class='hs-definition'>choice</span> <span class='hs-varid'>router1</span> <span class='hs-layout'>(</span><span class='hs-conid'>Choice</span> <span class='hs-varid'>router2</span> <span class='hs-varid'>router3</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Choice</span> <span class='hs-layout'>(</span><span class='hs-varid'>choice</span> <span class='hs-varid'>router1</span> <span class='hs-varid'>router2</span><span class='hs-layout'>)</span> <span class='hs-varid'>router3</span>
<a name="line-67"></a><span class='hs-definition'>choice</span> <span class='hs-varid'>router1</span> <span class='hs-varid'>router2</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Choice</span> <span class='hs-varid'>router1</span> <span class='hs-varid'>router2</span>
<a name="line-68"></a>
<a name="line-69"></a><a name="RouterStructure"></a><span class='hs-comment'>-- | Datatype used for representing and debugging the</span>
<a name="line-70"></a><a name="RouterStructure"></a><span class='hs-comment'>-- structure of a router. Abstracts from the handlers</span>
<a name="line-71"></a><a name="RouterStructure"></a><span class='hs-comment'>-- at the leaves.</span>
<a name="line-72"></a><a name="RouterStructure"></a><span class='hs-comment'>--</span>
<a name="line-73"></a><a name="RouterStructure"></a><span class='hs-comment'>-- Two 'Router's can be structurally compared by computing</span>
<a name="line-74"></a><a name="RouterStructure"></a><span class='hs-comment'>-- their 'RouterStructure' using 'routerStructure' and</span>
<a name="line-75"></a><a name="RouterStructure"></a><span class='hs-comment'>-- then testing for equality, see 'sameStructure'.</span>
<a name="line-76"></a><a name="RouterStructure"></a><span class='hs-comment'>--</span>
<a name="line-77"></a><a name="RouterStructure"></a><span class='hs-keyword'>data</span> <span class='hs-conid'>RouterStructure</span> <span class='hs-keyglyph'>=</span>
<a name="line-78"></a> <span class='hs-conid'>StaticRouterStructure</span> <span class='hs-layout'>(</span><span class='hs-conid'>Map</span> <span class='hs-conid'>Text</span> <span class='hs-conid'>RouterStructure</span><span class='hs-layout'>)</span> <span class='hs-conid'>Int</span>
<a name="line-79"></a> <span class='hs-keyglyph'>|</span> <span class='hs-conid'>CaptureRouterStructure</span> <span class='hs-conid'>RouterStructure</span>
<a name="line-80"></a> <span class='hs-keyglyph'>|</span> <span class='hs-conid'>RawRouterStructure</span>
<a name="line-81"></a> <span class='hs-keyglyph'>|</span> <span class='hs-conid'>ChoiceStructure</span> <span class='hs-conid'>RouterStructure</span> <span class='hs-conid'>RouterStructure</span>
<a name="line-82"></a> <span class='hs-keyword'>deriving</span> <span class='hs-layout'>(</span><span class='hs-conid'>Eq</span><span class='hs-layout'>,</span> <span class='hs-conid'>Show</span><span class='hs-layout'>)</span>
<a name="line-83"></a>
<a name="line-84"></a><a name="routerStructure"></a><span class='hs-comment'>-- | Compute the structure of a router.</span>
<a name="line-85"></a><span class='hs-comment'>--</span>
<a name="line-86"></a><span class='hs-comment'>-- Assumes that the request or text being passed</span>
<a name="line-87"></a><span class='hs-comment'>-- in 'WithRequest' or 'CaptureRouter' does not</span>
<a name="line-88"></a><span class='hs-comment'>-- affect the structure of the underlying tree.</span>
<a name="line-89"></a><span class='hs-comment'>--</span>
<a name="line-90"></a><span class='hs-definition'>routerStructure</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Router'</span> <span class='hs-varid'>env</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>RouterStructure</span>
<a name="line-91"></a><span class='hs-definition'>routerStructure</span> <span class='hs-layout'>(</span><span class='hs-conid'>StaticRouter</span> <span class='hs-varid'>m</span> <span class='hs-varid'>ls</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span>
<a name="line-92"></a> <span class='hs-conid'>StaticRouterStructure</span> <span class='hs-layout'>(</span><span class='hs-varid'>fmap</span> <span class='hs-varid'>routerStructure</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-varid'>length</span> <span class='hs-varid'>ls</span><span class='hs-layout'>)</span>
<a name="line-93"></a><span class='hs-definition'>routerStructure</span> <span class='hs-layout'>(</span><span class='hs-conid'>CaptureRouter</span> <span class='hs-varid'>router</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span>
<a name="line-94"></a> <span class='hs-conid'>CaptureRouterStructure</span> <span class='hs-varop'>$</span>
<a name="line-95"></a> <span class='hs-varid'>routerStructure</span> <span class='hs-varid'>router</span>
<a name="line-96"></a><span class='hs-definition'>routerStructure</span> <span class='hs-layout'>(</span><span class='hs-conid'>CaptureAllRouter</span> <span class='hs-varid'>router</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span>
<a name="line-97"></a> <span class='hs-conid'>CaptureRouterStructure</span> <span class='hs-varop'>$</span>
<a name="line-98"></a> <span class='hs-varid'>routerStructure</span> <span class='hs-varid'>router</span>
<a name="line-99"></a><span class='hs-definition'>routerStructure</span> <span class='hs-layout'>(</span><span class='hs-conid'>RawRouter</span> <span class='hs-keyword'>_</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span>
<a name="line-100"></a> <span class='hs-conid'>RawRouterStructure</span>
<a name="line-101"></a><span class='hs-definition'>routerStructure</span> <span class='hs-layout'>(</span><span class='hs-conid'>Choice</span> <span class='hs-varid'>r1</span> <span class='hs-varid'>r2</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span>
<a name="line-102"></a> <span class='hs-conid'>ChoiceStructure</span>
<a name="line-103"></a> <span class='hs-layout'>(</span><span class='hs-varid'>routerStructure</span> <span class='hs-varid'>r1</span><span class='hs-layout'>)</span>
<a name="line-104"></a> <span class='hs-layout'>(</span><span class='hs-varid'>routerStructure</span> <span class='hs-varid'>r2</span><span class='hs-layout'>)</span>
<a name="line-105"></a>
<a name="line-106"></a><a name="sameStructure"></a><span class='hs-comment'>-- | Compare the structure of two routers.</span>
<a name="line-107"></a><span class='hs-comment'>--</span>
<a name="line-108"></a><span class='hs-definition'>sameStructure</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Router'</span> <span class='hs-varid'>env</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Router'</span> <span class='hs-varid'>env</span> <span class='hs-varid'>b</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Bool</span>
<a name="line-109"></a><span class='hs-definition'>sameStructure</span> <span class='hs-varid'>r1</span> <span class='hs-varid'>r2</span> <span class='hs-keyglyph'>=</span>
<a name="line-110"></a> <span class='hs-varid'>routerStructure</span> <span class='hs-varid'>r1</span> <span class='hs-varop'>==</span> <span class='hs-varid'>routerStructure</span> <span class='hs-varid'>r2</span>
<a name="line-111"></a>
<a name="line-112"></a><a name="routerLayout"></a><span class='hs-comment'>-- | Provide a textual representation of the</span>
<a name="line-113"></a><span class='hs-comment'>-- structure of a router.</span>
<a name="line-114"></a><span class='hs-comment'>--</span>
<a name="line-115"></a><span class='hs-definition'>routerLayout</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Router'</span> <span class='hs-varid'>env</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Text</span>
<a name="line-116"></a><span class='hs-definition'>routerLayout</span> <span class='hs-varid'>router</span> <span class='hs-keyglyph'>=</span>
<a name="line-117"></a> <span class='hs-conid'>T</span><span class='hs-varop'>.</span><span class='hs-varid'>unlines</span> <span class='hs-layout'>(</span><span class='hs-keyglyph'>[</span><span class='hs-str'>"/"</span><span class='hs-keyglyph'>]</span> <span class='hs-varop'>++</span> <span class='hs-varid'>mkRouterLayout</span> <span class='hs-conid'>False</span> <span class='hs-layout'>(</span><span class='hs-varid'>routerStructure</span> <span class='hs-varid'>router</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span>
<a name="line-118"></a> <span class='hs-keyword'>where</span>
<a name="line-119"></a> <span class='hs-varid'>mkRouterLayout</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Bool</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>RouterStructure</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyglyph'>[</span><span class='hs-conid'>Text</span><span class='hs-keyglyph'>]</span>
<a name="line-120"></a> <span class='hs-varid'>mkRouterLayout</span> <span class='hs-varid'>c</span> <span class='hs-layout'>(</span><span class='hs-conid'>StaticRouterStructure</span> <span class='hs-varid'>m</span> <span class='hs-varid'>n</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>mkSubTrees</span> <span class='hs-varid'>c</span> <span class='hs-layout'>(</span><span class='hs-conid'>M</span><span class='hs-varop'>.</span><span class='hs-varid'>toList</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-varid'>n</span>
<a name="line-121"></a> <span class='hs-varid'>mkRouterLayout</span> <span class='hs-varid'>c</span> <span class='hs-layout'>(</span><span class='hs-conid'>CaptureRouterStructure</span> <span class='hs-varid'>r</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>mkSubTree</span> <span class='hs-varid'>c</span> <span class='hs-str'>"<capture>"</span> <span class='hs-layout'>(</span><span class='hs-varid'>mkRouterLayout</span> <span class='hs-conid'>False</span> <span class='hs-varid'>r</span><span class='hs-layout'>)</span>
<a name="line-122"></a> <span class='hs-varid'>mkRouterLayout</span> <span class='hs-varid'>c</span> <span class='hs-conid'>RawRouterStructure</span> <span class='hs-keyglyph'>=</span>
<a name="line-123"></a> <span class='hs-keyword'>if</span> <span class='hs-varid'>c</span> <span class='hs-keyword'>then</span> <span class='hs-keyglyph'>[</span><span class='hs-str'>"├─ <raw>"</span><span class='hs-keyglyph'>]</span> <span class='hs-keyword'>else</span> <span class='hs-keyglyph'>[</span><span class='hs-str'>"└─ <raw>"</span><span class='hs-keyglyph'>]</span>
<a name="line-124"></a> <span class='hs-varid'>mkRouterLayout</span> <span class='hs-varid'>c</span> <span class='hs-layout'>(</span><span class='hs-conid'>ChoiceStructure</span> <span class='hs-varid'>r1</span> <span class='hs-varid'>r2</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span>
<a name="line-125"></a> <span class='hs-varid'>mkRouterLayout</span> <span class='hs-conid'>True</span> <span class='hs-varid'>r1</span> <span class='hs-varop'>++</span> <span class='hs-keyglyph'>[</span><span class='hs-str'>"┆"</span><span class='hs-keyglyph'>]</span> <span class='hs-varop'>++</span> <span class='hs-varid'>mkRouterLayout</span> <span class='hs-varid'>c</span> <span class='hs-varid'>r2</span>
<a name="line-126"></a>
<a name="line-127"></a> <span class='hs-varid'>mkSubTrees</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Bool</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyglyph'>[</span><span class='hs-layout'>(</span><span class='hs-conid'>Text</span><span class='hs-layout'>,</span> <span class='hs-conid'>RouterStructure</span><span class='hs-layout'>)</span><span class='hs-keyglyph'>]</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Int</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyglyph'>[</span><span class='hs-conid'>Text</span><span class='hs-keyglyph'>]</span>
<a name="line-128"></a> <span class='hs-varid'>mkSubTrees</span> <span class='hs-keyword'>_</span> <span class='hs-conid'>[]</span> <span class='hs-num'>0</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>[]</span>
<a name="line-129"></a> <span class='hs-varid'>mkSubTrees</span> <span class='hs-varid'>c</span> <span class='hs-conid'>[]</span> <span class='hs-varid'>n</span> <span class='hs-keyglyph'>=</span>
<a name="line-130"></a> <span class='hs-varid'>concat</span> <span class='hs-layout'>(</span><span class='hs-varid'>replicate</span> <span class='hs-layout'>(</span><span class='hs-varid'>n</span> <span class='hs-comment'>-</span> <span class='hs-num'>1</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-varid'>mkLeaf</span> <span class='hs-conid'>True</span><span class='hs-layout'>)</span> <span class='hs-varop'>++</span> <span class='hs-keyglyph'>[</span><span class='hs-varid'>mkLeaf</span> <span class='hs-varid'>c</span><span class='hs-keyglyph'>]</span><span class='hs-layout'>)</span>
<a name="line-131"></a> <span class='hs-varid'>mkSubTrees</span> <span class='hs-varid'>c</span> <span class='hs-keyglyph'>[</span><span class='hs-layout'>(</span><span class='hs-varid'>t</span><span class='hs-layout'>,</span> <span class='hs-varid'>r</span><span class='hs-layout'>)</span><span class='hs-keyglyph'>]</span> <span class='hs-num'>0</span> <span class='hs-keyglyph'>=</span>
<a name="line-132"></a> <span class='hs-varid'>mkSubTree</span> <span class='hs-varid'>c</span> <span class='hs-varid'>t</span> <span class='hs-layout'>(</span><span class='hs-varid'>mkRouterLayout</span> <span class='hs-conid'>False</span> <span class='hs-varid'>r</span><span class='hs-layout'>)</span>
<a name="line-133"></a> <span class='hs-varid'>mkSubTrees</span> <span class='hs-varid'>c</span> <span class='hs-layout'>(</span><span class='hs-layout'>(</span><span class='hs-varid'>t</span><span class='hs-layout'>,</span> <span class='hs-varid'>r</span><span class='hs-layout'>)</span> <span class='hs-conop'>:</span> <span class='hs-varid'>trs</span><span class='hs-layout'>)</span> <span class='hs-varid'>n</span> <span class='hs-keyglyph'>=</span>
<a name="line-134"></a> <span class='hs-varid'>mkSubTree</span> <span class='hs-conid'>True</span> <span class='hs-varid'>t</span> <span class='hs-layout'>(</span><span class='hs-varid'>mkRouterLayout</span> <span class='hs-conid'>False</span> <span class='hs-varid'>r</span><span class='hs-layout'>)</span> <span class='hs-varop'>++</span> <span class='hs-varid'>mkSubTrees</span> <span class='hs-varid'>c</span> <span class='hs-varid'>trs</span> <span class='hs-varid'>n</span>
<a name="line-135"></a>
<a name="line-136"></a> <span class='hs-varid'>mkLeaf</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Bool</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyglyph'>[</span><span class='hs-conid'>Text</span><span class='hs-keyglyph'>]</span>
<a name="line-137"></a> <span class='hs-varid'>mkLeaf</span> <span class='hs-conid'>True</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyglyph'>[</span><span class='hs-str'>"├─•"</span><span class='hs-layout'>,</span><span class='hs-str'>"┆"</span><span class='hs-keyglyph'>]</span>
<a name="line-138"></a> <span class='hs-varid'>mkLeaf</span> <span class='hs-conid'>False</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyglyph'>[</span><span class='hs-str'>"└─•"</span><span class='hs-keyglyph'>]</span>
<a name="line-139"></a>
<a name="line-140"></a> <span class='hs-varid'>mkSubTree</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Bool</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Text</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyglyph'>[</span><span class='hs-conid'>Text</span><span class='hs-keyglyph'>]</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyglyph'>[</span><span class='hs-conid'>Text</span><span class='hs-keyglyph'>]</span>
<a name="line-141"></a> <span class='hs-varid'>mkSubTree</span> <span class='hs-conid'>True</span> <span class='hs-varid'>path</span> <span class='hs-varid'>children</span> <span class='hs-keyglyph'>=</span> <span class='hs-layout'>(</span><span class='hs-str'>"├─ "</span> <span class='hs-varop'><></span> <span class='hs-varid'>path</span> <span class='hs-varop'><></span> <span class='hs-str'>"/"</span><span class='hs-layout'>)</span> <span class='hs-conop'>:</span> <span class='hs-varid'>map</span> <span class='hs-layout'>(</span><span class='hs-str'>"│ "</span> <span class='hs-varop'><></span><span class='hs-layout'>)</span> <span class='hs-varid'>children</span>
<a name="line-142"></a> <span class='hs-varid'>mkSubTree</span> <span class='hs-conid'>False</span> <span class='hs-varid'>path</span> <span class='hs-varid'>children</span> <span class='hs-keyglyph'>=</span> <span class='hs-layout'>(</span><span class='hs-str'>"└─ "</span> <span class='hs-varop'><></span> <span class='hs-varid'>path</span> <span class='hs-varop'><></span> <span class='hs-str'>"/"</span><span class='hs-layout'>)</span> <span class='hs-conop'>:</span> <span class='hs-varid'>map</span> <span class='hs-layout'>(</span><span class='hs-str'>" "</span> <span class='hs-varop'><></span><span class='hs-layout'>)</span> <span class='hs-varid'>children</span>
<a name="line-143"></a>
<a name="line-144"></a><a name="tweakResponse"></a><span class='hs-comment'>-- | Apply a transformation to the response of a `Router`.</span>
<a name="line-145"></a><span class='hs-definition'>tweakResponse</span> <span class='hs-keyglyph'>::</span> <span class='hs-layout'>(</span><span class='hs-conid'>RouteResult</span> <span class='hs-conid'>Response</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>RouteResult</span> <span class='hs-conid'>Response</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Router</span> <span class='hs-varid'>env</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Router</span> <span class='hs-varid'>env</span>
<a name="line-146"></a><span class='hs-definition'>tweakResponse</span> <span class='hs-varid'>f</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>fmap</span> <span class='hs-layout'>(</span><span class='hs-keyglyph'>\</span><span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>req</span> <span class='hs-varid'>cont</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a</span> <span class='hs-varid'>req</span> <span class='hs-layout'>(</span><span class='hs-varid'>cont</span> <span class='hs-varop'>.</span> <span class='hs-varid'>f</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span>
<a name="line-147"></a>
<a name="line-148"></a><a name="runRouter"></a><span class='hs-comment'>-- | Interpret a router as an application.</span>
<a name="line-149"></a><span class='hs-definition'>runRouter</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Router</span> <span class='hs-conid'>()</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>RoutingApplication</span>
<a name="line-150"></a><span class='hs-definition'>runRouter</span> <span class='hs-varid'>r</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>runRouterEnv</span> <span class='hs-varid'>r</span> <span class='hs-conid'>()</span>
<a name="line-151"></a>
<a name="line-152"></a><a name="runRouterEnv"></a><span class='hs-definition'>runRouterEnv</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Router</span> <span class='hs-varid'>env</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>env</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>RoutingApplication</span>
<a name="line-153"></a><span class='hs-definition'>runRouterEnv</span> <span class='hs-varid'>router</span> <span class='hs-varid'>env</span> <span class='hs-varid'>request</span> <span class='hs-varid'>respond</span> <span class='hs-keyglyph'>=</span>
<a name="line-154"></a> <span class='hs-keyword'>case</span> <span class='hs-varid'>router</span> <span class='hs-keyword'>of</span>
<a name="line-155"></a> <span class='hs-conid'>StaticRouter</span> <span class='hs-varid'>table</span> <span class='hs-varid'>ls</span> <span class='hs-keyglyph'>-></span>
<a name="line-156"></a> <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-157"></a> <span class='hs-conid'>[]</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>runChoice</span> <span class='hs-varid'>ls</span> <span class='hs-varid'>env</span> <span class='hs-varid'>request</span> <span class='hs-varid'>respond</span>
<a name="line-158"></a> <span class='hs-comment'>-- This case is to handle trailing slashes.</span>
<a name="line-159"></a> <span class='hs-keyglyph'>[</span><span class='hs-str'>""</span><span class='hs-keyglyph'>]</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>runChoice</span> <span class='hs-varid'>ls</span> <span class='hs-varid'>env</span> <span class='hs-varid'>request</span> <span class='hs-varid'>respond</span>
<a name="line-160"></a> <span class='hs-varid'>first</span> <span class='hs-conop'>:</span> <span class='hs-varid'>rest</span> <span class='hs-keyglyph'>|</span> <span class='hs-conid'>Just</span> <span class='hs-varid'>router'</span> <span class='hs-keyglyph'><-</span> <span class='hs-conid'>M</span><span class='hs-varop'>.</span><span class='hs-varid'>lookup</span> <span class='hs-varid'>first</span> <span class='hs-varid'>table</span>
<a name="line-161"></a> <span class='hs-keyglyph'>-></span> <span class='hs-keyword'>let</span> <span class='hs-varid'>request'</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>request</span> <span class='hs-layout'>{</span> <span class='hs-varid'>pathInfo</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>rest</span> <span class='hs-layout'>}</span>
<a name="line-162"></a> <span class='hs-keyword'>in</span> <span class='hs-varid'>runRouterEnv</span> <span class='hs-varid'>router'</span> <span class='hs-varid'>env</span> <span class='hs-varid'>request'</span> <span class='hs-varid'>respond</span>
<a name="line-163"></a> <span class='hs-keyword'>_</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>respond</span> <span class='hs-varop'>$</span> <span class='hs-conid'>Fail</span> <span class='hs-varid'>err404</span>
<a name="line-164"></a> <span class='hs-conid'>CaptureRouter</span> <span class='hs-varid'>router'</span> <span class='hs-keyglyph'>-></span>
<a name="line-165"></a> <span class='hs-keyword'>case</span> <span class='hs-varid'>pathInfo</span> <span class='hs-varid'>request</span> <span class='hs-keyword'>of</span>
<a name="line-166"></a> <span class='hs-conid'>[]</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>respond</span> <span class='hs-varop'>$</span> <span class='hs-conid'>Fail</span> <span class='hs-varid'>err404</span>
<a name="line-167"></a> <span class='hs-comment'>-- This case is to handle trailing slashes.</span>
<a name="line-168"></a> <span class='hs-keyglyph'>[</span><span class='hs-str'>""</span><span class='hs-keyglyph'>]</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>respond</span> <span class='hs-varop'>$</span> <span class='hs-conid'>Fail</span> <span class='hs-varid'>err404</span>
<a name="line-169"></a> <span class='hs-varid'>first</span> <span class='hs-conop'>:</span> <span class='hs-varid'>rest</span>
<a name="line-170"></a> <span class='hs-keyglyph'>-></span> <span class='hs-keyword'>let</span> <span class='hs-varid'>request'</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>request</span> <span class='hs-layout'>{</span> <span class='hs-varid'>pathInfo</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>rest</span> <span class='hs-layout'>}</span>
<a name="line-171"></a> <span class='hs-keyword'>in</span> <span class='hs-varid'>runRouterEnv</span> <span class='hs-varid'>router'</span> <span class='hs-layout'>(</span><span class='hs-varid'>first</span><span class='hs-layout'>,</span> <span class='hs-varid'>env</span><span class='hs-layout'>)</span> <span class='hs-varid'>request'</span> <span class='hs-varid'>respond</span>
<a name="line-172"></a> <span class='hs-conid'>CaptureAllRouter</span> <span class='hs-varid'>router'</span> <span class='hs-keyglyph'>-></span>
<a name="line-173"></a> <span class='hs-keyword'>let</span> <span class='hs-varid'>segments</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>pathInfo</span> <span class='hs-varid'>request</span>
<a name="line-174"></a> <span class='hs-varid'>request'</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>request</span> <span class='hs-layout'>{</span> <span class='hs-varid'>pathInfo</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>[]</span> <span class='hs-layout'>}</span>
<a name="line-175"></a> <span class='hs-keyword'>in</span> <span class='hs-varid'>runRouterEnv</span> <span class='hs-varid'>router'</span> <span class='hs-layout'>(</span><span class='hs-varid'>segments</span><span class='hs-layout'>,</span> <span class='hs-varid'>env</span><span class='hs-layout'>)</span> <span class='hs-varid'>request'</span> <span class='hs-varid'>respond</span>
<a name="line-176"></a> <span class='hs-conid'>RawRouter</span> <span class='hs-varid'>app</span> <span class='hs-keyglyph'>-></span>
<a name="line-177"></a> <span class='hs-varid'>app</span> <span class='hs-varid'>env</span> <span class='hs-varid'>request</span> <span class='hs-varid'>respond</span>
<a name="line-178"></a> <span class='hs-conid'>Choice</span> <span class='hs-varid'>r1</span> <span class='hs-varid'>r2</span> <span class='hs-keyglyph'>-></span>
<a name="line-179"></a> <span class='hs-varid'>runChoice</span> <span class='hs-keyglyph'>[</span><span class='hs-varid'>runRouterEnv</span> <span class='hs-varid'>r1</span><span class='hs-layout'>,</span> <span class='hs-varid'>runRouterEnv</span> <span class='hs-varid'>r2</span><span class='hs-keyglyph'>]</span> <span class='hs-varid'>env</span> <span class='hs-varid'>request</span> <span class='hs-varid'>respond</span>
<a name="line-180"></a>
<a name="line-181"></a><a name="runChoice"></a><span class='hs-comment'>-- | Try a list of routing applications in order.</span>
<a name="line-182"></a><span class='hs-comment'>-- We stop as soon as one fails fatally or succeeds.</span>
<a name="line-183"></a><span class='hs-comment'>-- If all fail normally, we pick the "best" error.</span>
<a name="line-184"></a><span class='hs-comment'>--</span>
<a name="line-185"></a><span class='hs-definition'>runChoice</span> <span class='hs-keyglyph'>::</span> <span class='hs-keyglyph'>[</span><span class='hs-varid'>env</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>RoutingApplication</span><span class='hs-keyglyph'>]</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>env</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>RoutingApplication</span>
<a name="line-186"></a><span class='hs-definition'>runChoice</span> <span class='hs-varid'>ls</span> <span class='hs-keyglyph'>=</span>
<a name="line-187"></a> <span class='hs-keyword'>case</span> <span class='hs-varid'>ls</span> <span class='hs-keyword'>of</span>
<a name="line-188"></a> <span class='hs-conid'>[]</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyglyph'>\</span> <span class='hs-keyword'>_</span> <span class='hs-keyword'>_</span> <span class='hs-varid'>respond</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>respond</span> <span class='hs-layout'>(</span><span class='hs-conid'>Fail</span> <span class='hs-varid'>err404</span><span class='hs-layout'>)</span>
<a name="line-189"></a> <span class='hs-keyglyph'>[</span><span class='hs-varid'>r</span><span class='hs-keyglyph'>]</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>r</span>
<a name="line-190"></a> <span class='hs-layout'>(</span><span class='hs-varid'>r</span> <span class='hs-conop'>:</span> <span class='hs-varid'>rs</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span>
<a name="line-191"></a> <span class='hs-keyglyph'>\</span> <span class='hs-varid'>env</span> <span class='hs-varid'>request</span> <span class='hs-varid'>respond</span> <span class='hs-keyglyph'>-></span>
<a name="line-192"></a> <span class='hs-varid'>r</span> <span class='hs-varid'>env</span> <span class='hs-varid'>request</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span> <span class='hs-varid'>response1</span> <span class='hs-keyglyph'>-></span>
<a name="line-193"></a> <span class='hs-keyword'>case</span> <span class='hs-varid'>response1</span> <span class='hs-keyword'>of</span>
<a name="line-194"></a> <span class='hs-conid'>Fail</span> <span class='hs-keyword'>_</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>runChoice</span> <span class='hs-varid'>rs</span> <span class='hs-varid'>env</span> <span class='hs-varid'>request</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span> <span class='hs-varid'>response2</span> <span class='hs-keyglyph'>-></span>
<a name="line-195"></a> <span class='hs-varid'>respond</span> <span class='hs-varop'>$</span> <span class='hs-varid'>highestPri</span> <span class='hs-varid'>response1</span> <span class='hs-varid'>response2</span>
<a name="line-196"></a> <span class='hs-keyword'>_</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>respond</span> <span class='hs-varid'>response1</span>
<a name="line-197"></a> <span class='hs-keyword'>where</span>
<a name="line-198"></a> <span class='hs-varid'>highestPri</span> <span class='hs-layout'>(</span><span class='hs-conid'>Fail</span> <span class='hs-varid'>e1</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-conid'>Fail</span> <span class='hs-varid'>e2</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span>
<a name="line-199"></a> <span class='hs-keyword'>if</span> <span class='hs-varid'>worseHTTPCode</span> <span class='hs-layout'>(</span><span class='hs-varid'>errHTTPCode</span> <span class='hs-varid'>e1</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-varid'>errHTTPCode</span> <span class='hs-varid'>e2</span><span class='hs-layout'>)</span>
<a name="line-200"></a> <span class='hs-keyword'>then</span> <span class='hs-conid'>Fail</span> <span class='hs-varid'>e2</span>
<a name="line-201"></a> <span class='hs-keyword'>else</span> <span class='hs-conid'>Fail</span> <span class='hs-varid'>e1</span>
<a name="line-202"></a> <span class='hs-varid'>highestPri</span> <span class='hs-layout'>(</span><span class='hs-conid'>Fail</span> <span class='hs-keyword'>_</span><span class='hs-layout'>)</span> <span class='hs-varid'>y</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>y</span>
<a name="line-203"></a> <span class='hs-varid'>highestPri</span> <span class='hs-varid'>x</span> <span class='hs-keyword'>_</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>x</span>
<a name="line-204"></a>
<a name="line-205"></a><a name="worseHTTPCode"></a><span class='hs-comment'>-- Priority on HTTP codes.</span>
<a name="line-206"></a><span class='hs-comment'>--</span>
<a name="line-207"></a><span class='hs-comment'>-- It just so happens that 404 < 405 < 406 as far as</span>
<a name="line-208"></a><span class='hs-comment'>-- we are concerned here, so we can use (<).</span>
<a name="line-209"></a><span class='hs-definition'>worseHTTPCode</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Int</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Int</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Bool</span>
<a name="line-210"></a><span class='hs-definition'>worseHTTPCode</span> <span class='hs-keyglyph'>=</span> <span class='hs-layout'>(</span><span class='hs-varop'><</span><span class='hs-layout'>)</span>
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