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<pre><a name="line-1"></a><span class='hs-comment'>{-# LANGUAGE Rank2Types #-}</span>
<a name="line-2"></a><span class='hs-comment'>{-# LANGUAGE TypeFamilies #-}</span>
<a name="line-3"></a><span class='hs-comment'>{-# LANGUAGE MultiParamTypeClasses #-}</span>
<a name="line-4"></a><span class='hs-comment'>{-# LANGUAGE FlexibleInstances #-}</span>
<a name="line-5"></a><span class='hs-comment'>{-# LANGUAGE UndecidableInstances #-}</span>
<a name="line-6"></a><span class='hs-comment'>{-# LANGUAGE DeriveDataTypeable #-}</span>
<a name="line-7"></a><span class='hs-comment'>{-# LANGUAGE FlexibleContexts #-}</span>
<a name="line-8"></a><span class='hs-comment'>-- | Type classes for returning failures.</span>
<a name="line-9"></a><span class='hs-keyword'>module</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Failure</span>
<a name="line-10"></a> <span class='hs-layout'>(</span> <span class='hs-comment'>-- * Type class</span>
<a name="line-11"></a> <span class='hs-conid'>Failure</span> <span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span>
<a name="line-12"></a> <span class='hs-comment'>-- * Wrapping failures</span>
<a name="line-13"></a> <span class='hs-layout'>,</span> <span class='hs-conid'>WrapFailure</span> <span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span>
<a name="line-14"></a> <span class='hs-comment'>-- * Convenience 'String' failure</span>
<a name="line-15"></a> <span class='hs-layout'>,</span> <span class='hs-conid'>StringException</span> <span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span>
<a name="line-16"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>failureString</span>
<a name="line-17"></a> <span class='hs-comment'>-- * Convert 'Failure's into concrete types</span>
<a name="line-18"></a> <span class='hs-layout'>,</span> <span class='hs-conid'>Try</span> <span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span>
<a name="line-19"></a> <span class='hs-layout'>,</span> <span class='hs-conid'>NothingException</span> <span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span>
<a name="line-20"></a> <span class='hs-layout'>,</span> <span class='hs-conid'>NullException</span> <span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span>
<a name="line-21"></a> <span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-22"></a>
<a name="line-23"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Prelude</span> <span class='hs-varid'>hiding</span> <span class='hs-layout'>(</span><span class='hs-varid'>catch</span><span class='hs-layout'>)</span>
<a name="line-24"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Exception</span> <span class='hs-layout'>(</span><span class='hs-varid'>throw</span><span class='hs-layout'>,</span> <span class='hs-varid'>catch</span><span class='hs-layout'>,</span> <span class='hs-conid'>Exception</span><span class='hs-layout'>,</span> <span class='hs-conid'>SomeException</span> <span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span>
<a name="line-25"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Typeable</span> <span class='hs-layout'>(</span><span class='hs-conid'>Typeable</span><span class='hs-layout'>)</span>
<a name="line-26"></a>
<a name="line-27"></a><a name="Failure"></a><span class='hs-keyword'>class</span> <span class='hs-conid'>Monad</span> <span class='hs-varid'>f</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>Failure</span> <span class='hs-varid'>e</span> <span class='hs-varid'>f</span> <span class='hs-keyword'>where</span>
<a name="line-28"></a> <span class='hs-varid'>failure</span> <span class='hs-keyglyph'>::</span> <span class='hs-varid'>e</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>f</span> <span class='hs-varid'>v</span>
<a name="line-29"></a>
<a name="line-30"></a><a name="WrapFailure"></a><span class='hs-keyword'>class</span> <span class='hs-conid'>Failure</span> <span class='hs-varid'>e</span> <span class='hs-varid'>f</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>WrapFailure</span> <span class='hs-varid'>e</span> <span class='hs-varid'>f</span> <span class='hs-keyword'>where</span>
<a name="line-31"></a> <span class='hs-comment'>-- | Wrap the failure value, if any, with the given function. This is</span>
<a name="line-32"></a> <span class='hs-comment'>-- useful in particular when you want all the exceptions returned from a</span>
<a name="line-33"></a> <span class='hs-comment'>-- certain library to be of a certain type, even if they were generated by</span>
<a name="line-34"></a> <span class='hs-comment'>-- a different library.</span>
<a name="line-35"></a> <span class='hs-varid'>wrapFailure</span> <span class='hs-keyglyph'>::</span> <span class='hs-layout'>(</span><span class='hs-keyword'>forall</span> <span class='hs-varid'>eIn</span><span class='hs-varop'>.</span> <span class='hs-conid'>Exception</span> <span class='hs-varid'>eIn</span> <span class='hs-keyglyph'>=></span> <span class='hs-varid'>eIn</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>e</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>f</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>f</span> <span class='hs-varid'>a</span>
<a name="line-36"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Exception</span> <span class='hs-varid'>e</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>WrapFailure</span> <span class='hs-varid'>e</span> <span class='hs-conid'>IO</span> <span class='hs-keyword'>where</span>
<a name="line-37"></a> <span class='hs-varid'>wrapFailure</span> <span class='hs-varid'>f</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=</span>
<a name="line-38"></a> <span class='hs-varid'>m</span> <span class='hs-varop'>`catch`</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>e</span><span class='hs-keyglyph'>@</span><span class='hs-conid'>SomeException</span><span class='hs-layout'>{</span><span class='hs-layout'>}</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>throw</span> <span class='hs-layout'>(</span><span class='hs-varid'>f</span> <span class='hs-varid'>e</span><span class='hs-layout'>)</span>
<a name="line-39"></a>
<a name="line-40"></a><span class='hs-keyword'>class</span> <span class='hs-conid'>Try</span> <span class='hs-varid'>f</span> <span class='hs-keyword'>where</span>
<a name="line-41"></a> <span class='hs-keyword'>type</span> <span class='hs-conid'>Error</span> <span class='hs-varid'>f</span>
<a name="line-42"></a> <span class='hs-comment'>-- Turn a concrete failure into an abstract failure</span>
<a name="line-43"></a> <span class='hs-varid'>try</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Failure</span> <span class='hs-layout'>(</span><span class='hs-conid'>Error</span> <span class='hs-varid'>f</span><span class='hs-layout'>)</span> <span class='hs-varid'>f'</span> <span class='hs-keyglyph'>=></span> <span class='hs-varid'>f</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>f'</span> <span class='hs-varid'>a</span>
<a name="line-44"></a>
<a name="line-45"></a><a name="failureString"></a><span class='hs-comment'>-- | Call 'failure' with a 'String'.</span>
<a name="line-46"></a><span class='hs-definition'>failureString</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Failure</span> <span class='hs-conid'>StringException</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>String</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span>
<a name="line-47"></a><span class='hs-definition'>failureString</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>failure</span> <span class='hs-varop'>.</span> <span class='hs-conid'>StringException</span>
<a name="line-48"></a>
<a name="line-49"></a><a name="StringException"></a><span class='hs-keyword'>newtype</span> <span class='hs-conid'>StringException</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>StringException</span> <span class='hs-conid'>String</span>
<a name="line-50"></a> <span class='hs-keyword'>deriving</span> <span class='hs-conid'>Typeable</span>
<a name="line-51"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Show</span> <span class='hs-conid'>StringException</span> <span class='hs-keyword'>where</span>
<a name="line-52"></a> <span class='hs-varid'>show</span> <span class='hs-layout'>(</span><span class='hs-conid'>StringException</span> <span class='hs-varid'>s</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-str'>"StringException: "</span> <span class='hs-varop'>++</span> <span class='hs-varid'>s</span>
<a name="line-53"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Exception</span> <span class='hs-conid'>StringException</span>
<a name="line-54"></a>
<a name="line-55"></a><span class='hs-comment'>-- --------------</span>
<a name="line-56"></a><span class='hs-comment'>-- base instances</span>
<a name="line-57"></a><span class='hs-comment'>-- --------------</span>
<a name="line-58"></a>
<a name="line-59"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Failure</span> <span class='hs-varid'>e</span> <span class='hs-conid'>Maybe</span> <span class='hs-keyword'>where</span> <span class='hs-varid'>failure</span> <span class='hs-keyword'>_</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Nothing</span>
<a name="line-60"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Failure</span> <span class='hs-varid'>e</span> <span class='hs-conid'>[]</span> <span class='hs-keyword'>where</span> <span class='hs-varid'>failure</span> <span class='hs-keyword'>_</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>[]</span>
<a name="line-61"></a>
<a name="line-62"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Exception</span> <span class='hs-varid'>e</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>Failure</span> <span class='hs-varid'>e</span> <span class='hs-conid'>IO</span> <span class='hs-keyword'>where</span>
<a name="line-63"></a> <span class='hs-varid'>failure</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Exception</span><span class='hs-varop'>.</span><span class='hs-varid'>throw</span>
<a name="line-64"></a>
<a name="line-65"></a><span class='hs-comment'>-- not a monad or applicative instance Failure e (Either e) where failure = Left</span>
<a name="line-66"></a>
<a name="line-67"></a><a name="NothingException"></a><span class='hs-keyword'>data</span> <span class='hs-conid'>NothingException</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>NothingException</span>
<a name="line-68"></a> <span class='hs-keyword'>deriving</span> <span class='hs-layout'>(</span><span class='hs-conid'>Show</span><span class='hs-layout'>,</span> <span class='hs-conid'>Typeable</span><span class='hs-layout'>)</span>
<a name="line-69"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Exception</span> <span class='hs-conid'>NothingException</span>
<a name="line-70"></a>
<a name="line-71"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Try</span> <span class='hs-conid'>Maybe</span> <span class='hs-keyword'>where</span>
<a name="line-72"></a> <span class='hs-keyword'>type</span> <span class='hs-conid'>Error</span> <span class='hs-conid'>Maybe</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>NothingException</span>
<a name="line-73"></a> <span class='hs-varid'>try</span> <span class='hs-conid'>Nothing</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>failure</span> <span class='hs-conid'>NothingException</span>
<a name="line-74"></a> <span class='hs-varid'>try</span> <span class='hs-layout'>(</span><span class='hs-conid'>Just</span> <span class='hs-varid'>x</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>return</span> <span class='hs-varid'>x</span>
<a name="line-75"></a>
<a name="line-76"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Try</span> <span class='hs-layout'>(</span><span class='hs-conid'>Either</span> <span class='hs-varid'>e</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-77"></a> <span class='hs-keyword'>type</span> <span class='hs-conid'>Error</span> <span class='hs-layout'>(</span><span class='hs-conid'>Either</span> <span class='hs-varid'>e</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>e</span>
<a name="line-78"></a> <span class='hs-varid'>try</span> <span class='hs-layout'>(</span><span class='hs-conid'>Left</span> <span class='hs-varid'>e</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>failure</span> <span class='hs-varid'>e</span>
<a name="line-79"></a> <span class='hs-varid'>try</span> <span class='hs-layout'>(</span><span class='hs-conid'>Right</span> <span class='hs-varid'>x</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>return</span> <span class='hs-varid'>x</span>
<a name="line-80"></a>
<a name="line-81"></a><a name="NullException"></a><span class='hs-keyword'>data</span> <span class='hs-conid'>NullException</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>NullException</span>
<a name="line-82"></a> <span class='hs-keyword'>deriving</span> <span class='hs-layout'>(</span><span class='hs-conid'>Show</span><span class='hs-layout'>,</span> <span class='hs-conid'>Typeable</span><span class='hs-layout'>)</span>
<a name="line-83"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Exception</span> <span class='hs-conid'>NullException</span>
<a name="line-84"></a>
<a name="line-85"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Try</span> <span class='hs-conid'>[]</span> <span class='hs-keyword'>where</span>
<a name="line-86"></a> <span class='hs-keyword'>type</span> <span class='hs-conid'>Error</span> <span class='hs-conid'>[]</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>NullException</span>
<a name="line-87"></a> <span class='hs-varid'>try</span> <span class='hs-conid'>[]</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>failure</span> <span class='hs-conid'>NullException</span>
<a name="line-88"></a> <span class='hs-varid'>try</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'>return</span> <span class='hs-varid'>x</span>
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