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Imported from c-m-f, new Failure based class
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{-# LANGUAGE Rank2Types #-} | ||
{-# LANGUAGE MultiParamTypeClasses #-} | ||
{-# LANGUAGE FlexibleInstances #-} | ||
{-# LANGUAGE UndecidableInstances #-} | ||
{-# LANGUAGE DeriveDataTypeable #-} | ||
{-# LANGUAGE FlexibleContexts #-} | ||
-- | Type classes for returning failures. | ||
module Control.Failure | ||
( -- * Type classes | ||
Failure (..) | ||
, FunctorFailure | ||
, ApplicativeFailure | ||
, MonadFailure | ||
-- * Wrapping failures | ||
, WrapFailure (..) | ||
-- * Convenience 'String' failure | ||
, StringException (..) | ||
, failureString | ||
) where | ||
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import Control.Exception (throw, Exception) | ||
import Data.Typeable (Typeable) | ||
import Control.Applicative (Applicative) | ||
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class Failure e f where | ||
failure :: e -> f v | ||
class (Functor f, Failure e f) => FunctorFailure e f | ||
class (Applicative f, Failure e f) => ApplicativeFailure e f | ||
class (Monad f, Applicative f, Failure e f) => MonadFailure e f | ||
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-- These introduce the need to use undecidables and overlapping. | ||
-- However, since they are merely type synonyms, this is acceptable. | ||
instance (Functor f, Failure e f) => FunctorFailure e f | ||
instance (Applicative f, Failure e f) => ApplicativeFailure e f | ||
instance (Monad f, Applicative f, Failure e f) => MonadFailure e f | ||
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class Failure e f => WrapFailure e f where | ||
-- | Wrap the failure value, if any, with the given function. This is | ||
-- useful in particular when you want all the exceptions returned from a | ||
-- certain library to be of a certain type, even if they were generated by | ||
-- a different library. | ||
wrapFailure :: (forall eIn. Exception eIn => eIn -> e) -> f a -> f a | ||
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-- | Call 'failure' with a 'String'. | ||
failureString :: MonadFailure StringException m => String -> m a | ||
failureString = failure . StringException | ||
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newtype StringException = StringException String | ||
deriving Typeable | ||
instance Show StringException where | ||
show (StringException s) = "StringException: " ++ s | ||
instance Exception StringException | ||
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-- -------------- | ||
-- base instances | ||
-- -------------- | ||
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instance Failure e Maybe where failure _ = Nothing | ||
instance Failure e [] where failure _ = [] | ||
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instance Exception e => Failure e IO where | ||
failure = Control.Exception.throw |
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name: failure | ||
version: 0.0.0 | ||
Cabal-Version: >= 1.6 | ||
build-type: Simple | ||
license: PublicDomain | ||
author: Pepe Iborra, Michael Snoyman, Nicolas Pouillard | ||
maintainer: pepeiborra@gmail.com | ||
homepage: http://github.com/snoyberg/failure | ||
description: Typeclass for representing failures | ||
synopsis: Typeclass for representing failures | ||
category: Control, Monads, Failure | ||
stability: stable | ||
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Library | ||
buildable: True | ||
build-depends: base >= 4 && < 5 | ||
ghc-options: -Wall | ||
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exposed-modules: | ||
Control.Failure | ||
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source-repository head | ||
type: git | ||
location: git://github.com/snoyberg/failure.git |