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<pre><a name="line-1"></a><span class='hs-comment'>{-# LANGUAGE UndecidableInstances #-}</span>
<a name="line-2"></a>
<a name="line-3"></a><span class='hs-comment'>{- |
<a name="line-4"></a>Module : Control.Monad.Error.Class
<a name="line-5"></a>Copyright : (c) Michael Weber <michael.weber@post.rwth-aachen.de> 2001,
<a name="line-6"></a> (c) Jeff Newbern 2003-2006,
<a name="line-7"></a> (c) Andriy Palamarchuk 2006
<a name="line-8"></a>License : BSD-style (see the file LICENSE)
<a name="line-9"></a>
<a name="line-10"></a>Maintainer : libraries@haskell.org
<a name="line-11"></a>Stability : experimental
<a name="line-12"></a>Portability : non-portable (multi-parameter type classes)
<a name="line-13"></a>
<a name="line-14"></a>[Computation type:] Computations which may fail or throw exceptions.
<a name="line-15"></a>
<a name="line-16"></a>[Binding strategy:] Failure records information about the cause\/location
<a name="line-17"></a>of the failure. Failure values bypass the bound function,
<a name="line-18"></a>other values are used as inputs to the bound function.
<a name="line-19"></a>
<a name="line-20"></a>[Useful for:] Building computations from sequences of functions that may fail
<a name="line-21"></a>or using exception handling to structure error handling.
<a name="line-22"></a>
<a name="line-23"></a>[Zero and plus:] Zero is represented by an empty error and the plus operation
<a name="line-24"></a>executes its second argument if the first fails.
<a name="line-25"></a>
<a name="line-26"></a>[Example type:] @'Either' 'String' a@
<a name="line-27"></a>
<a name="line-28"></a>The Error monad (also called the Exception monad).
<a name="line-29"></a>-}</span>
<a name="line-30"></a>
<a name="line-31"></a><span class='hs-comment'>{-
<a name="line-32"></a> Rendered by Michael Weber <mailto:michael.weber@post.rwth-aachen.de>,
<a name="line-33"></a> inspired by the Haskell Monad Template Library from
<a name="line-34"></a> Andy Gill (<<a href="http://web.cecs.pdx.edu/~andy/">http://web.cecs.pdx.edu/~andy/</a>>)
<a name="line-35"></a>-}</span>
<a name="line-36"></a><span class='hs-keyword'>module</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Monad</span><span class='hs-varop'>.</span><span class='hs-conid'>Error</span><span class='hs-varop'>.</span><span class='hs-conid'>Class</span> <span class='hs-layout'>(</span>
<a name="line-37"></a> <span class='hs-conid'>Error</span><span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span><span class='hs-layout'>,</span>
<a name="line-38"></a> <span class='hs-conid'>MonadError</span><span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span><span class='hs-layout'>,</span>
<a name="line-39"></a> <span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-40"></a>
<a name="line-41"></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-varop'>.</span><span class='hs-conid'>Trans</span><span class='hs-varop'>.</span><span class='hs-conid'>Error</span> <span class='hs-layout'>(</span><span class='hs-conid'>Error</span><span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span><span class='hs-layout'>,</span> <span class='hs-conid'>ErrorT</span><span class='hs-layout'>)</span>
<a name="line-42"></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'>Monad</span><span class='hs-varop'>.</span><span class='hs-conid'>Trans</span><span class='hs-varop'>.</span><span class='hs-conid'>Error</span> <span class='hs-keyword'>as</span> <span class='hs-conid'>ErrorT</span> <span class='hs-layout'>(</span><span class='hs-varid'>throwError</span><span class='hs-layout'>,</span> <span class='hs-varid'>catchError</span><span class='hs-layout'>)</span>
<a name="line-43"></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-varop'>.</span><span class='hs-conid'>Trans</span><span class='hs-varop'>.</span><span class='hs-conid'>Identity</span> <span class='hs-keyword'>as</span> <span class='hs-conid'>Identity</span>
<a name="line-44"></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-varop'>.</span><span class='hs-conid'>Trans</span><span class='hs-varop'>.</span><span class='hs-conid'>List</span> <span class='hs-keyword'>as</span> <span class='hs-conid'>List</span>
<a name="line-45"></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-varop'>.</span><span class='hs-conid'>Trans</span><span class='hs-varop'>.</span><span class='hs-conid'>Maybe</span> <span class='hs-keyword'>as</span> <span class='hs-conid'>Maybe</span>
<a name="line-46"></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-varop'>.</span><span class='hs-conid'>Trans</span><span class='hs-varop'>.</span><span class='hs-conid'>Reader</span> <span class='hs-keyword'>as</span> <span class='hs-conid'>Reader</span>
<a name="line-47"></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-varop'>.</span><span class='hs-conid'>Trans</span><span class='hs-varop'>.</span><span class='hs-conid'>RWS</span><span class='hs-varop'>.</span><span class='hs-conid'>Lazy</span> <span class='hs-keyword'>as</span> <span class='hs-conid'>LazyRWS</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-varop'>.</span><span class='hs-conid'>Trans</span><span class='hs-varop'>.</span><span class='hs-conid'>RWS</span><span class='hs-varop'>.</span><span class='hs-conid'>Strict</span> <span class='hs-keyword'>as</span> <span class='hs-conid'>StrictRWS</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'>Monad</span><span class='hs-varop'>.</span><span class='hs-conid'>Trans</span><span class='hs-varop'>.</span><span class='hs-conid'>State</span><span class='hs-varop'>.</span><span class='hs-conid'>Lazy</span> <span class='hs-keyword'>as</span> <span class='hs-conid'>LazyState</span>
<a name="line-50"></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-varop'>.</span><span class='hs-conid'>Trans</span><span class='hs-varop'>.</span><span class='hs-conid'>State</span><span class='hs-varop'>.</span><span class='hs-conid'>Strict</span> <span class='hs-keyword'>as</span> <span class='hs-conid'>StrictState</span>
<a name="line-51"></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-varop'>.</span><span class='hs-conid'>Trans</span><span class='hs-varop'>.</span><span class='hs-conid'>Writer</span><span class='hs-varop'>.</span><span class='hs-conid'>Lazy</span> <span class='hs-keyword'>as</span> <span class='hs-conid'>LazyWriter</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'>Monad</span><span class='hs-varop'>.</span><span class='hs-conid'>Trans</span><span class='hs-varop'>.</span><span class='hs-conid'>Writer</span><span class='hs-varop'>.</span><span class='hs-conid'>Strict</span> <span class='hs-keyword'>as</span> <span class='hs-conid'>StrictWriter</span>
<a name="line-53"></a>
<a name="line-54"></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-varop'>.</span><span class='hs-conid'>Trans</span><span class='hs-varop'>.</span><span class='hs-conid'>Class</span> <span class='hs-layout'>(</span><span class='hs-varid'>lift</span><span class='hs-layout'>)</span>
<a name="line-55"></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-conid'>IOException</span><span class='hs-layout'>)</span>
<a name="line-56"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Monad</span>
<a name="line-57"></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-varop'>.</span><span class='hs-conid'>Instances</span> <span class='hs-conid'>()</span>
<a name="line-58"></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-59"></a>
<a name="line-60"></a><a name="MonadError"></a><span class='hs-comment'>{- |
<a name="line-61"></a>The strategy of combining computations that can throw exceptions
<a name="line-62"></a>by bypassing bound functions
<a name="line-63"></a>from the point an exception is thrown to the point that it is handled.
<a name="line-64"></a>
<a name="line-65"></a>Is parameterized over the type of error information and
<a name="line-66"></a>the monad type constructor.
<a name="line-67"></a>It is common to use @'Data.Either' String@ as the monad type constructor
<a name="line-68"></a>for an error monad in which error descriptions take the form of strings.
<a name="line-69"></a>In that case and many other common cases the resulting monad is already defined
<a name="line-70"></a>as an instance of the 'MonadError' class.
<a name="line-71"></a>You can also define your own error type and\/or use a monad type constructor
<a name="line-72"></a>other than @'Either' 'String'@ or @'Either' 'IOError'@.
<a name="line-73"></a>In these cases you will have to explicitly define instances of the 'Error'
<a name="line-74"></a>and\/or 'MonadError' classes.
<a name="line-75"></a>-}</span>
<a name="line-76"></a><a name="MonadError"></a><span class='hs-keyword'>class</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-conid'>MonadError</span> <span class='hs-varid'>e</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>|</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>e</span> <span class='hs-keyword'>where</span>
<a name="line-77"></a> <span class='hs-comment'>-- | Is used within a monadic computation to begin exception processing.</span>
<a name="line-78"></a> <span class='hs-varid'>throwError</span> <span class='hs-keyglyph'>::</span> <span class='hs-varid'>e</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span>
<a name="line-79"></a>
<a name="line-80"></a> <span class='hs-comment'>{- |
<a name="line-81"></a> A handler function to handle previous errors and return to normal execution.
<a name="line-82"></a> A common idiom is:
<a name="line-83"></a>
<a name="line-84"></a> > do { action1; action2; action3 } `catchError` handler
<a name="line-85"></a>
<a name="line-86"></a> where the @action@ functions can call 'throwError'.
<a name="line-87"></a> Note that @handler@ and the do-block must have the same return type.
<a name="line-88"></a> -}</span>
<a name="line-89"></a> <span class='hs-varid'>catchError</span> <span class='hs-keyglyph'>::</span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</span><span class='hs-varid'>e</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span>
<a name="line-90"></a>
<a name="line-91"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>MonadError</span> <span class='hs-conid'>IOException</span> <span class='hs-conid'>IO</span> <span class='hs-keyword'>where</span>
<a name="line-92"></a> <span class='hs-varid'>throwError</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>ioError</span>
<a name="line-93"></a> <span class='hs-varid'>catchError</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>catch</span>
<a name="line-94"></a>
<a name="line-95"></a><span class='hs-comment'>-- ---------------------------------------------------------------------------</span>
<a name="line-96"></a><span class='hs-comment'>-- Our parameterizable error monad</span>
<a name="line-97"></a>
<a name="line-98"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>Error</span> <span class='hs-varid'>e</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadError</span> <span class='hs-varid'>e</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-99"></a> <span class='hs-varid'>throwError</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Left</span>
<a name="line-100"></a> <span class='hs-conid'>Left</span> <span class='hs-varid'>l</span> <span class='hs-varop'>`catchError`</span> <span class='hs-varid'>h</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>h</span> <span class='hs-varid'>l</span>
<a name="line-101"></a> <span class='hs-conid'>Right</span> <span class='hs-varid'>r</span> <span class='hs-varop'>`catchError`</span> <span class='hs-keyword'>_</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Right</span> <span class='hs-varid'>r</span>
<a name="line-102"></a>
<a name="line-103"></a><span class='hs-keyword'>instance</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-conid'>Error</span> <span class='hs-varid'>e</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadError</span> <span class='hs-varid'>e</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorT</span> <span class='hs-varid'>e</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-104"></a> <span class='hs-varid'>throwError</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ErrorT</span><span class='hs-varop'>.</span><span class='hs-varid'>throwError</span>
<a name="line-105"></a> <span class='hs-varid'>catchError</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ErrorT</span><span class='hs-varop'>.</span><span class='hs-varid'>catchError</span>
<a name="line-106"></a>
<a name="line-107"></a><span class='hs-comment'>-- ---------------------------------------------------------------------------</span>
<a name="line-108"></a><span class='hs-comment'>-- Instances for other mtl transformers</span>
<a name="line-109"></a><span class='hs-comment'>--</span>
<a name="line-110"></a><span class='hs-comment'>-- All of these instances need UndecidableInstances,</span>
<a name="line-111"></a><span class='hs-comment'>-- because they do not satisfy the coverage condition.</span>
<a name="line-112"></a>
<a name="line-113"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>MonadError</span> <span class='hs-varid'>e</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadError</span> <span class='hs-varid'>e</span> <span class='hs-layout'>(</span><span class='hs-conid'>IdentityT</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-114"></a> <span class='hs-varid'>throwError</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>lift</span> <span class='hs-varop'>.</span> <span class='hs-varid'>throwError</span>
<a name="line-115"></a> <span class='hs-varid'>catchError</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Identity</span><span class='hs-varop'>.</span><span class='hs-varid'>liftCatch</span> <span class='hs-varid'>catchError</span>
<a name="line-116"></a>
<a name="line-117"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>MonadError</span> <span class='hs-varid'>e</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadError</span> <span class='hs-varid'>e</span> <span class='hs-layout'>(</span><span class='hs-conid'>ListT</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-118"></a> <span class='hs-varid'>throwError</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>lift</span> <span class='hs-varop'>.</span> <span class='hs-varid'>throwError</span>
<a name="line-119"></a> <span class='hs-varid'>catchError</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>List</span><span class='hs-varop'>.</span><span class='hs-varid'>liftCatch</span> <span class='hs-varid'>catchError</span>
<a name="line-120"></a>
<a name="line-121"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>MonadError</span> <span class='hs-varid'>e</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadError</span> <span class='hs-varid'>e</span> <span class='hs-layout'>(</span><span class='hs-conid'>MaybeT</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-122"></a> <span class='hs-varid'>throwError</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>lift</span> <span class='hs-varop'>.</span> <span class='hs-varid'>throwError</span>
<a name="line-123"></a> <span class='hs-varid'>catchError</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Maybe</span><span class='hs-varop'>.</span><span class='hs-varid'>liftCatch</span> <span class='hs-varid'>catchError</span>
<a name="line-124"></a>
<a name="line-125"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>MonadError</span> <span class='hs-varid'>e</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadError</span> <span class='hs-varid'>e</span> <span class='hs-layout'>(</span><span class='hs-conid'>ReaderT</span> <span class='hs-varid'>r</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-126"></a> <span class='hs-varid'>throwError</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>lift</span> <span class='hs-varop'>.</span> <span class='hs-varid'>throwError</span>
<a name="line-127"></a> <span class='hs-varid'>catchError</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Reader</span><span class='hs-varop'>.</span><span class='hs-varid'>liftCatch</span> <span class='hs-varid'>catchError</span>
<a name="line-128"></a>
<a name="line-129"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>Monoid</span> <span class='hs-varid'>w</span><span class='hs-layout'>,</span> <span class='hs-conid'>MonadError</span> <span class='hs-varid'>e</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadError</span> <span class='hs-varid'>e</span> <span class='hs-layout'>(</span><span class='hs-conid'>LazyRWS</span><span class='hs-varop'>.</span><span class='hs-conid'>RWST</span> <span class='hs-varid'>r</span> <span class='hs-varid'>w</span> <span class='hs-varid'>s</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-130"></a> <span class='hs-varid'>throwError</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>lift</span> <span class='hs-varop'>.</span> <span class='hs-varid'>throwError</span>
<a name="line-131"></a> <span class='hs-varid'>catchError</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>LazyRWS</span><span class='hs-varop'>.</span><span class='hs-varid'>liftCatch</span> <span class='hs-varid'>catchError</span>
<a name="line-132"></a>
<a name="line-133"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>Monoid</span> <span class='hs-varid'>w</span><span class='hs-layout'>,</span> <span class='hs-conid'>MonadError</span> <span class='hs-varid'>e</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadError</span> <span class='hs-varid'>e</span> <span class='hs-layout'>(</span><span class='hs-conid'>StrictRWS</span><span class='hs-varop'>.</span><span class='hs-conid'>RWST</span> <span class='hs-varid'>r</span> <span class='hs-varid'>w</span> <span class='hs-varid'>s</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-134"></a> <span class='hs-varid'>throwError</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>lift</span> <span class='hs-varop'>.</span> <span class='hs-varid'>throwError</span>
<a name="line-135"></a> <span class='hs-varid'>catchError</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>StrictRWS</span><span class='hs-varop'>.</span><span class='hs-varid'>liftCatch</span> <span class='hs-varid'>catchError</span>
<a name="line-136"></a>
<a name="line-137"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>MonadError</span> <span class='hs-varid'>e</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadError</span> <span class='hs-varid'>e</span> <span class='hs-layout'>(</span><span class='hs-conid'>LazyState</span><span class='hs-varop'>.</span><span class='hs-conid'>StateT</span> <span class='hs-varid'>s</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-138"></a> <span class='hs-varid'>throwError</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>lift</span> <span class='hs-varop'>.</span> <span class='hs-varid'>throwError</span>
<a name="line-139"></a> <span class='hs-varid'>catchError</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>LazyState</span><span class='hs-varop'>.</span><span class='hs-varid'>liftCatch</span> <span class='hs-varid'>catchError</span>
<a name="line-140"></a>
<a name="line-141"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>MonadError</span> <span class='hs-varid'>e</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadError</span> <span class='hs-varid'>e</span> <span class='hs-layout'>(</span><span class='hs-conid'>StrictState</span><span class='hs-varop'>.</span><span class='hs-conid'>StateT</span> <span class='hs-varid'>s</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-142"></a> <span class='hs-varid'>throwError</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>lift</span> <span class='hs-varop'>.</span> <span class='hs-varid'>throwError</span>
<a name="line-143"></a> <span class='hs-varid'>catchError</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>StrictState</span><span class='hs-varop'>.</span><span class='hs-varid'>liftCatch</span> <span class='hs-varid'>catchError</span>
<a name="line-144"></a>
<a name="line-145"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>Monoid</span> <span class='hs-varid'>w</span><span class='hs-layout'>,</span> <span class='hs-conid'>MonadError</span> <span class='hs-varid'>e</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadError</span> <span class='hs-varid'>e</span> <span class='hs-layout'>(</span><span class='hs-conid'>LazyWriter</span><span class='hs-varop'>.</span><span class='hs-conid'>WriterT</span> <span class='hs-varid'>w</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-146"></a> <span class='hs-varid'>throwError</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>lift</span> <span class='hs-varop'>.</span> <span class='hs-varid'>throwError</span>
<a name="line-147"></a> <span class='hs-varid'>catchError</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>LazyWriter</span><span class='hs-varop'>.</span><span class='hs-varid'>liftCatch</span> <span class='hs-varid'>catchError</span>
<a name="line-148"></a>
<a name="line-149"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>Monoid</span> <span class='hs-varid'>w</span><span class='hs-layout'>,</span> <span class='hs-conid'>MonadError</span> <span class='hs-varid'>e</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadError</span> <span class='hs-varid'>e</span> <span class='hs-layout'>(</span><span class='hs-conid'>StrictWriter</span><span class='hs-varop'>.</span><span class='hs-conid'>WriterT</span> <span class='hs-varid'>w</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-150"></a> <span class='hs-varid'>throwError</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>lift</span> <span class='hs-varop'>.</span> <span class='hs-varid'>throwError</span>
<a name="line-151"></a> <span class='hs-varid'>catchError</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>StrictWriter</span><span class='hs-varop'>.</span><span class='hs-varid'>liftCatch</span> <span class='hs-varid'>catchError</span>
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