<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html>
<head>
<!-- Generated by HsColour, http://www.cs.york.ac.uk/fp/darcs/hscolour/ -->
<title>Data/Attempt.hs</title>
<link type='text/css' rel='stylesheet' href='hscolour.css' />
</head>
<body>
<pre><a name="line-1"></a><span class='hs-comment'>{-# LANGUAGE MultiParamTypeClasses #-}</span>
<a name="line-2"></a><span class='hs-comment'>{-# LANGUAGE DeriveDataTypeable #-}</span>
<a name="line-3"></a><span class='hs-comment'>{-# LANGUAGE ExistentialQuantification #-}</span>
<a name="line-4"></a><span class='hs-comment'>{-# LANGUAGE FlexibleInstances #-}</span>
<a name="line-5"></a><span class='hs-comment'>{-# LANGUAGE Rank2Types #-}</span>
<a name="line-6"></a><span class='hs-comment'>---------------------------------------------------------</span>
<a name="line-7"></a><span class='hs-comment'>--</span>
<a name="line-8"></a><span class='hs-comment'>-- Module : Data.Attempt</span>
<a name="line-9"></a><span class='hs-comment'>-- Copyright : Michael Snoyman</span>
<a name="line-10"></a><span class='hs-comment'>-- License : BSD3</span>
<a name="line-11"></a><span class='hs-comment'>--</span>
<a name="line-12"></a><span class='hs-comment'>-- Maintainer : Michael Snoyman <michael@snoyman.com></span>
<a name="line-13"></a><span class='hs-comment'>-- Stability : Unstable</span>
<a name="line-14"></a><span class='hs-comment'>-- Portability : portable</span>
<a name="line-15"></a><span class='hs-comment'>--</span>
<a name="line-16"></a><span class='hs-comment'>-- A universal data type for computations which may fail.</span>
<a name="line-17"></a><span class='hs-comment'>---------------------------------------------------------</span>
<a name="line-18"></a>
<a name="line-19"></a><span class='hs-comment'>-- | A universal data type for computations which may fail. Errors are reported</span>
<a name="line-20"></a><span class='hs-comment'>-- using extensible exceptions. These exceptions are not explicitly stated; if</span>
<a name="line-21"></a><span class='hs-comment'>-- you want this kind of functionality, something like control-monad-exception</span>
<a name="line-22"></a><span class='hs-comment'>-- might be a more appropriate fit.</span>
<a name="line-23"></a><span class='hs-keyword'>module</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Attempt</span>
<a name="line-24"></a> <span class='hs-layout'>(</span> <span class='hs-comment'>-- * Data type and type class</span>
<a name="line-25"></a> <span class='hs-conid'>Attempt</span> <span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span>
<a name="line-26"></a> <span class='hs-layout'>,</span> <span class='hs-conid'>FromAttempt</span> <span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span>
<a name="line-27"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>fa</span>
<a name="line-28"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>joinAttempt</span>
<a name="line-29"></a> <span class='hs-comment'>-- * General handling of 'Attempt's</span>
<a name="line-30"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>attempt</span>
<a name="line-31"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>makeHandler</span>
<a name="line-32"></a> <span class='hs-layout'>,</span> <span class='hs-conid'>AttemptHandler</span> <span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span>
<a name="line-33"></a> <span class='hs-comment'>-- * Individual 'Attempt's</span>
<a name="line-34"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>isFailure</span>
<a name="line-35"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>isSuccess</span>
<a name="line-36"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>fromSuccess</span>
<a name="line-37"></a> <span class='hs-comment'>-- * Lists of 'Attempt's</span>
<a name="line-38"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>successes</span>
<a name="line-39"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>failures</span>
<a name="line-40"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>partitionAttempts</span>
<a name="line-41"></a> <span class='hs-comment'>-- * Runtime exceptions</span>
<a name="line-42"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>attemptIO</span>
<a name="line-43"></a> <span class='hs-comment'>-- * Reexport the 'Failure' class</span>
<a name="line-44"></a> <span class='hs-layout'>,</span> <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-45"></a> <span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-46"></a>
<a name="line-47"></a><span class='hs-keyword'>import</span> <span class='hs-keyword'>qualified</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Exception</span> <span class='hs-keyword'>as</span> <span class='hs-conid'>E</span>
<a name="line-48"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Monad</span> <span class='hs-layout'>(</span><span class='hs-varid'>ap</span><span class='hs-layout'>)</span>
<a name="line-49"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Applicative</span>
<a name="line-50"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Data</span>
<a name="line-51"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Either</span> <span class='hs-layout'>(</span><span class='hs-varid'>lefts</span><span class='hs-layout'>)</span>
<a name="line-52"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Failure</span>
<a name="line-53"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>GHC</span><span class='hs-varop'>.</span><span class='hs-conid'>Show</span> <span class='hs-layout'>(</span><span class='hs-varid'>appPrec</span><span class='hs-layout'>,</span> <span class='hs-varid'>appPrec1</span><span class='hs-layout'>)</span>
<a name="line-54"></a><a name="Attempt"></a><span class='hs-comment'>-- | Contains either a 'Success' value or a 'Failure' exception.</span>
<a name="line-55"></a><a name="Attempt"></a><span class='hs-keyword'>data</span> <span class='hs-conid'>Attempt</span> <span class='hs-varid'>v</span>
<a name="line-56"></a> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Success</span> <span class='hs-varid'>v</span>
<a name="line-57"></a> <span class='hs-keyglyph'>|</span> <span class='hs-keyword'>forall</span> <span class='hs-varid'>e</span><span class='hs-varop'>.</span> <span class='hs-conid'>E</span><span class='hs-varop'>.</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>
<a name="line-58"></a> <span class='hs-keyword'>deriving</span> <span class='hs-layout'>(</span><span class='hs-conid'>Typeable</span><span class='hs-layout'>)</span>
<a name="line-59"></a>
<a name="line-60"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Show</span> <span class='hs-varid'>v</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>Show</span> <span class='hs-layout'>(</span><span class='hs-conid'>Attempt</span> <span class='hs-varid'>v</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-61"></a> <span class='hs-varid'>showsPrec</span> <span class='hs-varid'>p</span> <span class='hs-layout'>(</span><span class='hs-conid'>Success</span> <span class='hs-varid'>v</span><span class='hs-layout'>)</span>
<a name="line-62"></a> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>showParen</span> <span class='hs-layout'>(</span><span class='hs-varid'>p</span> <span class='hs-varop'>></span> <span class='hs-varid'>appPrec</span><span class='hs-layout'>)</span> <span class='hs-varop'>$</span> <span class='hs-varid'>showString</span> <span class='hs-str'>"Success "</span> <span class='hs-varop'>.</span> <span class='hs-varid'>showsPrec</span> <span class='hs-varid'>appPrec1</span> <span class='hs-varid'>v</span>
<a name="line-63"></a> <span class='hs-varid'>showsPrec</span> <span class='hs-varid'>p</span> <span class='hs-layout'>(</span><span class='hs-conid'>Failure</span> <span class='hs-varid'>v</span><span class='hs-layout'>)</span>
<a name="line-64"></a> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>showParen</span> <span class='hs-layout'>(</span><span class='hs-varid'>p</span> <span class='hs-varop'>></span> <span class='hs-varid'>appPrec</span><span class='hs-layout'>)</span> <span class='hs-varop'>$</span>
<a name="line-65"></a> <span class='hs-varid'>showString</span> <span class='hs-str'>"Failure "</span> <span class='hs-varop'>.</span> <span class='hs-varid'>showsPrec</span> <span class='hs-varid'>appPrec1</span> <span class='hs-varid'>v</span>
<a name="line-66"></a>
<a name="line-67"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Functor</span> <span class='hs-conid'>Attempt</span> <span class='hs-keyword'>where</span>
<a name="line-68"></a> <span class='hs-varid'>fmap</span> <span class='hs-varid'>f</span> <span class='hs-layout'>(</span><span class='hs-conid'>Success</span> <span class='hs-varid'>v</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Success</span> <span class='hs-varop'>$</span> <span class='hs-varid'>f</span> <span class='hs-varid'>v</span>
<a name="line-69"></a> <span class='hs-varid'>fmap</span> <span class='hs-keyword'>_</span> <span class='hs-layout'>(</span><span class='hs-conid'>Failure</span> <span class='hs-varid'>e</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Failure</span> <span class='hs-varid'>e</span>
<a name="line-70"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Applicative</span> <span class='hs-conid'>Attempt</span> <span class='hs-keyword'>where</span>
<a name="line-71"></a> <span class='hs-varid'>pure</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Success</span>
<a name="line-72"></a> <span class='hs-layout'>(</span><span class='hs-varop'><*></span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>ap</span>
<a name="line-73"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Monad</span> <span class='hs-conid'>Attempt</span> <span class='hs-keyword'>where</span>
<a name="line-74"></a> <span class='hs-varid'>return</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Success</span>
<a name="line-75"></a> <span class='hs-layout'>(</span><span class='hs-conid'>Success</span> <span class='hs-varid'>v</span><span class='hs-layout'>)</span> <span class='hs-varop'>>>=</span> <span class='hs-varid'>f</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>f</span> <span class='hs-varid'>v</span>
<a name="line-76"></a> <span class='hs-layout'>(</span><span class='hs-conid'>Failure</span> <span class='hs-varid'>e</span><span class='hs-layout'>)</span> <span class='hs-varop'>>>=</span> <span class='hs-keyword'>_</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Failure</span> <span class='hs-varid'>e</span>
<a name="line-77"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>E</span><span class='hs-varop'>.</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'>Attempt</span> <span class='hs-keyword'>where</span>
<a name="line-78"></a> <span class='hs-varid'>failure</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Failure</span>
<a name="line-79"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>E</span><span class='hs-varop'>.</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'>Attempt</span> <span class='hs-keyword'>where</span>
<a name="line-80"></a> <span class='hs-varid'>wrapFailure</span> <span class='hs-keyword'>_</span> <span class='hs-layout'>(</span><span class='hs-conid'>Success</span> <span class='hs-varid'>v</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Success</span> <span class='hs-varid'>v</span>
<a name="line-81"></a> <span class='hs-varid'>wrapFailure</span> <span class='hs-varid'>f</span> <span class='hs-layout'>(</span><span class='hs-conid'>Failure</span> <span class='hs-varid'>e</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Failure</span> <span class='hs-varop'>$</span> <span class='hs-varid'>f</span> <span class='hs-varid'>e</span>
<a name="line-82"></a>
<a name="line-83"></a><a name="Attempt"></a><span class='hs-comment'>-- | Any type which can be converted from an 'Attempt'. The included instances are your \"usual suspects\" for dealing with error handling. They include:</span>
<a name="line-84"></a><a name="Attempt"></a><span class='hs-comment'>--</span>
<a name="line-85"></a><a name="Attempt"></a><span class='hs-comment'>-- 'IO': For the IO instance, any exceptions in the 'Attempt' are thrown as</span>
<a name="line-86"></a><a name="Attempt"></a><span class='hs-comment'>-- runtime exceptions.</span>
<a name="line-87"></a><a name="Attempt"></a><span class='hs-comment'>--</span>
<a name="line-88"></a><a name="Attempt"></a><span class='hs-comment'>-- 'Maybe': Returns 'Nothing' on 'Failure', or 'Just' on 'Success'.</span>
<a name="line-89"></a><a name="Attempt"></a><span class='hs-comment'>--</span>
<a name="line-90"></a><a name="Attempt"></a><span class='hs-comment'>-- List: Returns the empty list on 'Failure', or a singleton list on 'Success'.</span>
<a name="line-91"></a><a name="Attempt"></a><span class='hs-comment'>--</span>
<a name="line-92"></a><a name="Attempt"></a><span class='hs-comment'>-- 'Either' 'String': Returns 'Left' ('show' exception) on 'Failure', or 'Right' on</span>
<a name="line-93"></a><a name="Attempt"></a><span class='hs-comment'>-- 'Success'.</span>
<a name="line-94"></a><a name="Attempt"></a><span class='hs-comment'>--</span>
<a name="line-95"></a><a name="Attempt"></a><span class='hs-comment'>-- 'Either' 'E.Exception': Returns 'Left' exception on 'Failure', or 'Right' on</span>
<a name="line-96"></a><a name="Attempt"></a><span class='hs-comment'>-- 'Success'.</span>
<a name="line-97"></a><a name="Attempt"></a><span class='hs-keyword'>class</span> <span class='hs-conid'>FromAttempt</span> <span class='hs-varid'>a</span> <span class='hs-keyword'>where</span>
<a name="line-98"></a> <span class='hs-varid'>fromAttempt</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Attempt</span> <span class='hs-varid'>v</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a</span> <span class='hs-varid'>v</span>
<a name="line-99"></a>
<a name="line-100"></a><a name="fa"></a><span class='hs-comment'>-- | A shortcut for 'fromAttempt'.</span>
<a name="line-101"></a><span class='hs-definition'>fa</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>FromAttempt</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>Attempt</span> <span class='hs-varid'>v</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a</span> <span class='hs-varid'>v</span>
<a name="line-102"></a><span class='hs-definition'>fa</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>fromAttempt</span>
<a name="line-103"></a>
<a name="line-104"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>FromAttempt</span> <span class='hs-conid'>IO</span> <span class='hs-keyword'>where</span>
<a name="line-105"></a> <span class='hs-varid'>fromAttempt</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>attempt</span> <span class='hs-conid'>E</span><span class='hs-varop'>.</span><span class='hs-varid'>throwIO</span> <span class='hs-varid'>return</span>
<a name="line-106"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>FromAttempt</span> <span class='hs-conid'>Maybe</span> <span class='hs-keyword'>where</span>
<a name="line-107"></a> <span class='hs-varid'>fromAttempt</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>attempt</span> <span class='hs-layout'>(</span><span class='hs-varid'>const</span> <span class='hs-conid'>Nothing</span><span class='hs-layout'>)</span> <span class='hs-conid'>Just</span>
<a name="line-108"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>FromAttempt</span> <span class='hs-conid'>[]</span> <span class='hs-keyword'>where</span>
<a name="line-109"></a> <span class='hs-varid'>fromAttempt</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>attempt</span> <span class='hs-layout'>(</span><span class='hs-varid'>const</span> <span class='hs-conid'>[]</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-conop'>:</span> <span class='hs-conid'>[]</span><span class='hs-layout'>)</span>
<a name="line-110"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>FromAttempt</span> <span class='hs-layout'>(</span><span class='hs-conid'>Either</span> <span class='hs-conid'>String</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-111"></a> <span class='hs-varid'>fromAttempt</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>attempt</span> <span class='hs-layout'>(</span><span class='hs-conid'>Left</span> <span class='hs-varop'>.</span> <span class='hs-varid'>show</span><span class='hs-layout'>)</span> <span class='hs-conid'>Right</span>
<a name="line-112"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>FromAttempt</span> <span class='hs-layout'>(</span><span class='hs-conid'>Either</span> <span class='hs-conid'>E</span><span class='hs-varop'>.</span><span class='hs-conid'>SomeException</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-113"></a> <span class='hs-varid'>fromAttempt</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>attempt</span> <span class='hs-layout'>(</span><span class='hs-conid'>Left</span> <span class='hs-varop'>.</span> <span class='hs-conid'>E</span><span class='hs-varop'>.</span><span class='hs-varid'>toException</span><span class='hs-layout'>)</span> <span class='hs-conid'>Right</span>
<a name="line-114"></a>
<a name="line-115"></a><a name="joinAttempt"></a><span class='hs-comment'>-- | This is not a simple translation of the Control.Monad.join function.</span>
<a name="line-116"></a><span class='hs-comment'>-- Instead, for 'Monad's which are instances of 'FromAttempt', it removes the</span>
<a name="line-117"></a><span class='hs-comment'>-- inner 'Attempt' type, reporting errors as defined in the 'FromAttempt'</span>
<a name="line-118"></a><span class='hs-comment'>-- instance.</span>
<a name="line-119"></a><span class='hs-comment'>--</span>
<a name="line-120"></a><span class='hs-comment'>-- For example, join (Just (failureString \"foo\")) == Nothing.</span>
<a name="line-121"></a><span class='hs-definition'>joinAttempt</span> <span class='hs-keyglyph'>::</span> <span class='hs-layout'>(</span><span class='hs-conid'>FromAttempt</span> <span class='hs-varid'>m</span><span class='hs-layout'>,</span> <span class='hs-conid'>Monad</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-varid'>m</span> <span class='hs-layout'>(</span><span class='hs-conid'>Attempt</span> <span class='hs-varid'>v</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-varid'>v</span>
<a name="line-122"></a><span class='hs-definition'>joinAttempt</span> <span class='hs-keyglyph'>=</span> <span class='hs-layout'>(</span><span class='hs-varop'>>>=</span> <span class='hs-varid'>fromAttempt</span><span class='hs-layout'>)</span>
<a name="line-123"></a>
<a name="line-124"></a><a name="attempt"></a><span class='hs-comment'>-- | Process either the exception or value in an 'Attempt' to produce a result.</span>
<a name="line-125"></a><span class='hs-comment'>--</span>
<a name="line-126"></a><span class='hs-comment'>-- This function is modeled after 'maybe' and 'either'. The first argument must</span>
<a name="line-127"></a><span class='hs-comment'>-- accept any instances of 'E.Exception'. If you want to handle multiple types</span>
<a name="line-128"></a><span class='hs-comment'>-- of exceptions, see 'makeHandler'. The second argument converts the success</span>
<a name="line-129"></a><span class='hs-comment'>-- value.</span>
<a name="line-130"></a><span class='hs-comment'>--</span>
<a name="line-131"></a><span class='hs-comment'>-- Note that this function does not expose all the data available in an</span>
<a name="line-132"></a><span class='hs-comment'>-- 'Attempt' value. Notably, the monadic stack trace is not passed on to the</span>
<a name="line-133"></a><span class='hs-comment'>-- error handler. If desired, use the 'monadicStackTrace' function to extract</span>
<a name="line-134"></a><span class='hs-comment'>-- it.</span>
<a name="line-135"></a><span class='hs-definition'>attempt</span> <span class='hs-keyglyph'>::</span> <span class='hs-layout'>(</span><span class='hs-keyword'>forall</span> <span class='hs-varid'>e</span><span class='hs-varop'>.</span> <span class='hs-conid'>E</span><span class='hs-varop'>.</span><span class='hs-conid'>Exception</span> <span class='hs-varid'>e</span> <span class='hs-keyglyph'>=></span> <span class='hs-varid'>e</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>b</span><span class='hs-layout'>)</span> <span class='hs-comment'>-- ^ error handler</span>
<a name="line-136"></a> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>b</span><span class='hs-layout'>)</span> <span class='hs-comment'>-- ^ success handler</span>
<a name="line-137"></a> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Attempt</span> <span class='hs-varid'>a</span>
<a name="line-138"></a> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>b</span>
<a name="line-139"></a><span class='hs-definition'>attempt</span> <span class='hs-keyword'>_</span> <span class='hs-varid'>f</span> <span class='hs-layout'>(</span><span class='hs-conid'>Success</span> <span class='hs-varid'>v</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>f</span> <span class='hs-varid'>v</span>
<a name="line-140"></a><span class='hs-definition'>attempt</span> <span class='hs-varid'>f</span> <span class='hs-keyword'>_</span> <span class='hs-layout'>(</span><span class='hs-conid'>Failure</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'>e</span>
<a name="line-141"></a>
<a name="line-142"></a><a name="makeHandler"></a><span class='hs-comment'>-- | Convert multiple 'AttemptHandler's and a default value into an exception</span>
<a name="line-143"></a><span class='hs-comment'>-- handler.</span>
<a name="line-144"></a><span class='hs-comment'>--</span>
<a name="line-145"></a><span class='hs-comment'>-- This is a convenience function when you want to have special handling for a</span>
<a name="line-146"></a><span class='hs-comment'>-- few types of 'E.Exception's and provide another value for anything else.</span>
<a name="line-147"></a><span class='hs-definition'>makeHandler</span> <span class='hs-keyglyph'>::</span> <span class='hs-keyglyph'>[</span><span class='hs-conid'>AttemptHandler</span> <span class='hs-varid'>v</span><span class='hs-keyglyph'>]</span>
<a name="line-148"></a> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>v</span>
<a name="line-149"></a> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</span><span class='hs-keyword'>forall</span> <span class='hs-varid'>e</span><span class='hs-varop'>.</span> <span class='hs-conid'>E</span><span class='hs-varop'>.</span><span class='hs-conid'>Exception</span> <span class='hs-varid'>e</span> <span class='hs-keyglyph'>=></span> <span class='hs-varid'>e</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>v</span><span class='hs-layout'>)</span>
<a name="line-150"></a><span class='hs-definition'>makeHandler</span> <span class='hs-conid'>[]</span> <span class='hs-varid'>v</span> <span class='hs-keyword'>_</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>v</span>
<a name="line-151"></a><span class='hs-definition'>makeHandler</span> <span class='hs-layout'>(</span><span class='hs-conid'>AttemptHandler</span> <span class='hs-varid'>h</span><span class='hs-conop'>:</span><span class='hs-varid'>hs</span><span class='hs-layout'>)</span> <span class='hs-varid'>v</span> <span class='hs-varid'>e</span> <span class='hs-keyglyph'>=</span>
<a name="line-152"></a> <span class='hs-keyword'>case</span> <span class='hs-conid'>E</span><span class='hs-varop'>.</span><span class='hs-varid'>fromException</span> <span class='hs-layout'>(</span><span class='hs-conid'>E</span><span class='hs-varop'>.</span><span class='hs-varid'>toException</span> <span class='hs-varid'>e</span><span class='hs-layout'>)</span> <span class='hs-keyword'>of</span>
<a name="line-153"></a> <span class='hs-conid'>Just</span> <span class='hs-varid'>e'</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>h</span> <span class='hs-varid'>e'</span>
<a name="line-154"></a> <span class='hs-conid'>Nothing</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>makeHandler</span> <span class='hs-varid'>hs</span> <span class='hs-varid'>v</span> <span class='hs-varid'>e</span>
<a name="line-155"></a>
<a name="line-156"></a><a name="AttemptHandler"></a><span class='hs-comment'>-- | A simple wrapper value necesary due to the Haskell type system. Wraps a</span>
<a name="line-157"></a><a name="AttemptHandler"></a><span class='hs-comment'>-- function from a *specific* 'E.Exception' type to some value.</span>
<a name="line-158"></a><a name="AttemptHandler"></a><span class='hs-keyword'>data</span> <span class='hs-conid'>AttemptHandler</span> <span class='hs-varid'>v</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>forall</span> <span class='hs-varid'>e</span><span class='hs-varop'>.</span> <span class='hs-conid'>E</span><span class='hs-varop'>.</span><span class='hs-conid'>Exception</span> <span class='hs-varid'>e</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>AttemptHandler</span> <span class='hs-layout'>(</span><span class='hs-varid'>e</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>v</span><span class='hs-layout'>)</span>
<a name="line-159"></a>
<a name="line-160"></a><a name="isFailure"></a><span class='hs-comment'>-- | Tests for a 'Failure' value.</span>
<a name="line-161"></a><span class='hs-definition'>isFailure</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Attempt</span> <span class='hs-varid'>v</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Bool</span>
<a name="line-162"></a><span class='hs-definition'>isFailure</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>attempt</span> <span class='hs-layout'>(</span><span class='hs-varid'>const</span> <span class='hs-conid'>True</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-varid'>const</span> <span class='hs-conid'>False</span><span class='hs-layout'>)</span>
<a name="line-163"></a>
<a name="line-164"></a><a name="isSuccess"></a><span class='hs-comment'>-- | Tests for a 'Success' value.</span>
<a name="line-165"></a><span class='hs-definition'>isSuccess</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Attempt</span> <span class='hs-varid'>v</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Bool</span>
<a name="line-166"></a><span class='hs-definition'>isSuccess</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>attempt</span> <span class='hs-layout'>(</span><span class='hs-varid'>const</span> <span class='hs-conid'>False</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-varid'>const</span> <span class='hs-conid'>True</span><span class='hs-layout'>)</span>
<a name="line-167"></a>
<a name="line-168"></a><a name="fromSuccess"></a><span class='hs-comment'>-- | This is an unsafe, partial function which should only be used if you</span>
<a name="line-169"></a><span class='hs-comment'>-- either know that a function will succeed or don't mind the occassional</span>
<a name="line-170"></a><span class='hs-comment'>-- runtime exception.</span>
<a name="line-171"></a><span class='hs-definition'>fromSuccess</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Attempt</span> <span class='hs-varid'>v</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>v</span>
<a name="line-172"></a><span class='hs-definition'>fromSuccess</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>attempt</span> <span class='hs-layout'>(</span><span class='hs-varid'>error</span> <span class='hs-varop'>.</span> <span class='hs-varid'>show</span><span class='hs-layout'>)</span> <span class='hs-varid'>id</span>
<a name="line-173"></a>
<a name="line-174"></a><a name="successes"></a><span class='hs-comment'>-- | Returns only the 'Success' values.</span>
<a name="line-175"></a><span class='hs-definition'>successes</span> <span class='hs-keyglyph'>::</span> <span class='hs-keyglyph'>[</span><span class='hs-conid'>Attempt</span> <span class='hs-varid'>v</span><span class='hs-keyglyph'>]</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyglyph'>[</span><span class='hs-varid'>v</span><span class='hs-keyglyph'>]</span>
<a name="line-176"></a><span class='hs-definition'>successes</span> <span class='hs-varid'>l</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyglyph'>[</span> <span class='hs-varid'>v</span> <span class='hs-keyglyph'>|</span> <span class='hs-conid'>Success</span> <span class='hs-varid'>v</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>l</span> <span class='hs-keyglyph'>]</span>
<a name="line-177"></a>
<a name="line-178"></a><a name="failures"></a><span class='hs-comment'>-- | Returns only the 'Failure' values, each wrapped in a 'SomeException'.</span>
<a name="line-179"></a><span class='hs-definition'>failures</span> <span class='hs-keyglyph'>::</span> <span class='hs-keyglyph'>[</span><span class='hs-conid'>Attempt</span> <span class='hs-varid'>v</span><span class='hs-keyglyph'>]</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyglyph'>[</span><span class='hs-conid'>E</span><span class='hs-varop'>.</span><span class='hs-conid'>SomeException</span><span class='hs-keyglyph'>]</span>
<a name="line-180"></a><span class='hs-definition'>failures</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>lefts</span> <span class='hs-varop'>.</span> <span class='hs-varid'>map</span> <span class='hs-varid'>eitherExceptionFromAttempt</span> <span class='hs-keyword'>where</span>
<a name="line-181"></a> <span class='hs-varid'>eitherExceptionFromAttempt</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Attempt</span> <span class='hs-varid'>v</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Either</span> <span class='hs-conid'>E</span><span class='hs-varop'>.</span><span class='hs-conid'>SomeException</span> <span class='hs-varid'>v</span>
<a name="line-182"></a> <span class='hs-varid'>eitherExceptionFromAttempt</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>fa</span>
<a name="line-183"></a>
<a name="line-184"></a><a name="partitionAttempts"></a><span class='hs-comment'>-- | Return all of the 'Failure's and 'Success'es separately in a tuple.</span>
<a name="line-185"></a><span class='hs-definition'>partitionAttempts</span> <span class='hs-keyglyph'>::</span> <span class='hs-keyglyph'>[</span><span class='hs-conid'>Attempt</span> <span class='hs-varid'>v</span><span class='hs-keyglyph'>]</span> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</span><span class='hs-keyglyph'>[</span><span class='hs-conid'>E</span><span class='hs-varop'>.</span><span class='hs-conid'>SomeException</span><span class='hs-keyglyph'>]</span><span class='hs-layout'>,</span> <span class='hs-keyglyph'>[</span><span class='hs-varid'>v</span><span class='hs-keyglyph'>]</span><span class='hs-layout'>)</span>
<a name="line-186"></a><span class='hs-definition'>partitionAttempts</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>foldr</span> <span class='hs-layout'>(</span><span class='hs-varid'>attempt</span> <span class='hs-varid'>f</span> <span class='hs-varid'>s</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-conid'>[]</span><span class='hs-layout'>,</span><span class='hs-conid'>[]</span><span class='hs-layout'>)</span>
<a name="line-187"></a> <span class='hs-keyword'>where</span>
<a name="line-188"></a> <span class='hs-varid'>f</span> <span class='hs-varid'>a</span> <span class='hs-layout'>(</span><span class='hs-varid'>l</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-layout'>(</span><span class='hs-conid'>E</span><span class='hs-varop'>.</span><span class='hs-varid'>toException</span> <span class='hs-varid'>a</span><span class='hs-conop'>:</span><span class='hs-varid'>l</span><span class='hs-layout'>,</span> <span class='hs-varid'>r</span><span class='hs-layout'>)</span>
<a name="line-189"></a> <span class='hs-varid'>s</span> <span class='hs-varid'>a</span> <span class='hs-layout'>(</span><span class='hs-varid'>l</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-layout'>(</span><span class='hs-varid'>l</span><span class='hs-layout'>,</span> <span class='hs-varid'>a</span><span class='hs-conop'>:</span><span class='hs-varid'>r</span><span class='hs-layout'>)</span>
<a name="line-190"></a>
<a name="line-191"></a><a name="attemptIO"></a><span class='hs-comment'>-- | Catches runtime (ie, IO) exceptions and inserts them into an 'Attempt'.</span>
<a name="line-192"></a><span class='hs-comment'>--</span>
<a name="line-193"></a><span class='hs-comment'>-- Like 'handle', the first argument to this function must explicitly state the</span>
<a name="line-194"></a><span class='hs-comment'>-- type of its input.</span>
<a name="line-195"></a><span class='hs-definition'>attemptIO</span> <span class='hs-keyglyph'>::</span> <span class='hs-layout'>(</span><span class='hs-conid'>E</span><span class='hs-varop'>.</span><span class='hs-conid'>Exception</span> <span class='hs-varid'>eIn</span><span class='hs-layout'>,</span> <span class='hs-conid'>E</span><span class='hs-varop'>.</span><span class='hs-conid'>Exception</span> <span class='hs-varid'>eOut</span><span class='hs-layout'>)</span>
<a name="line-196"></a> <span class='hs-keyglyph'>=></span> <span class='hs-layout'>(</span><span class='hs-varid'>eIn</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>eOut</span><span class='hs-layout'>)</span>
<a name="line-197"></a> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>IO</span> <span class='hs-varid'>v</span>
<a name="line-198"></a> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>IO</span> <span class='hs-layout'>(</span><span class='hs-conid'>Attempt</span> <span class='hs-varid'>v</span><span class='hs-layout'>)</span>
<a name="line-199"></a><span class='hs-definition'>attemptIO</span> <span class='hs-varid'>f</span> <span class='hs-keyglyph'>=</span>
<a name="line-200"></a> <span class='hs-conid'>E</span><span class='hs-varop'>.</span><span class='hs-varid'>handle</span> <span class='hs-layout'>(</span><span class='hs-varid'>return</span> <span class='hs-varop'>.</span> <span class='hs-conid'>Failure</span> <span class='hs-varop'>.</span> <span class='hs-varid'>f</span><span class='hs-layout'>)</span>
<a name="line-201"></a> <span class='hs-varop'>.</span> <span class='hs-varid'>fmap</span> <span class='hs-conid'>Success</span>
</pre></body>
</html>
