Copyright	(C) Edward Kmett 2013-2015 (c) Google Inc. 2012
License	BSD-style (see the file LICENSE)
Maintainer	Edward Kmett <ekmett@gmail.com>
Stability	experimental
Portability	non-portable
Safe Haskell	Trustworthy
Language	Haskell98

Control.Monad.Catch.Pure

Contents

Transformer
Typeclass

Description

This module supplies a 'pure' monad transformer that can be used for mock-testing code that throws exceptions, so long as those exceptions are always thrown with throwM .

Do not mix CatchT with IO . Choose one or the other for the bottom of your transformer stack!

Synopsis

newtype CatchT m a = CatchT {
- runCatchT :: m ( Either SomeException a)
}
type Catch = CatchT Identity
runCatch :: Catch a -> Either SomeException a
mapCatchT :: (m ( Either SomeException a) -> n ( Either SomeException b)) -> CatchT m a -> CatchT n b
module Control.Monad.Catch

Transformer

The transformers -style monad transfomer

newtype CatchT m a Source #

Add Exception handling abilities to a Monad .

This should never be used in combination with IO . Think of CatchT as an alternative base monad for use with mocking code that solely throws exceptions via throwM .

Note: that IO monad has these abilities already, so stacking CatchT on top of it does not add any value and can possibly be confusing:

>>> (error "Hello!" :: IO ()) `catch` (\(e :: ErrorCall) -> liftIO $ print e)
Hello!

>>> runCatchT $ (error "Hello!" :: CatchT IO ()) `catch` (\(e :: ErrorCall) -> liftIO $ print e)
*** Exception: Hello!

>>> runCatchT $ (throwM (ErrorCall "Hello!") :: CatchT IO ()) `catch` (\(e :: ErrorCall) -> liftIO $ print e)
Hello!

Constructors

CatchT
Fields runCatchT :: m ( Either SomeException a)

Instances

Instances details

MonadTrans CatchT Source #
Instance details Defined in Control.Monad.Catch.Pure Methods lift :: Monad m => m a -> CatchT m a Source #
MonadRWS r w s m => MonadRWS r w s ( CatchT m) Source #
Instance details Defined in Control.Monad.Catch.Pure
MonadWriter w m => MonadWriter w ( CatchT m) Source #
Instance details Defined in Control.Monad.Catch.Pure Methods writer :: (a, w) -> CatchT m a Source # tell :: w -> CatchT m () Source # listen :: CatchT m a -> CatchT m (a, w) Source # pass :: CatchT m (a, w -> w) -> CatchT m a Source #
MonadState s m => MonadState s ( CatchT m) Source #
Instance details Defined in Control.Monad.Catch.Pure Methods get :: CatchT m s Source # put :: s -> CatchT m () Source # state :: (s -> (a, s)) -> CatchT m a Source #
MonadReader e m => MonadReader e ( CatchT m) Source #
Instance details Defined in Control.Monad.Catch.Pure Methods ask :: CatchT m e Source # local :: (e -> e) -> CatchT m a -> CatchT m a Source # reader :: (e -> a) -> CatchT m a Source #
Monad m => Monad ( CatchT m) Source #
Instance details Defined in Control.Monad.Catch.Pure Methods (>>=) :: CatchT m a -> (a -> CatchT m b) -> CatchT m b Source # (>>) :: CatchT m a -> CatchT m b -> CatchT m b Source # return :: a -> CatchT m a Source #
Monad m => Functor ( CatchT m) Source #
Instance details Defined in Control.Monad.Catch.Pure Methods fmap :: (a -> b) -> CatchT m a -> CatchT m b Source # (<$) :: a -> CatchT m b -> CatchT m a Source #
MonadFix m => MonadFix ( CatchT m) Source #
Instance details Defined in Control.Monad.Catch.Pure Methods mfix :: (a -> CatchT m a) -> CatchT m a Source #
Monad m => MonadFail ( CatchT m) Source #
Instance details Defined in Control.Monad.Catch.Pure Methods fail :: String -> CatchT m a Source #
Monad m => Applicative ( CatchT m) Source #
Instance details Defined in Control.Monad.Catch.Pure Methods pure :: a -> CatchT m a Source # (<>) :: CatchT m (a -> b) -> CatchT m a -> CatchT m b Source # liftA2 :: (a -> b -> c) -> CatchT m a -> CatchT m b -> CatchT m c Source # (>) :: CatchT m a -> CatchT m b -> CatchT m b Source # (<*) :: CatchT m a -> CatchT m b -> CatchT m a Source #
Foldable m => Foldable ( CatchT m) Source #
Instance details Defined in Control.Monad.Catch.Pure Methods fold :: Monoid m0 => CatchT m m0 -> m0 Source # foldMap :: Monoid m0 => (a -> m0) -> CatchT m a -> m0 Source # foldMap' :: Monoid m0 => (a -> m0) -> CatchT m a -> m0 Source # foldr :: (a -> b -> b) -> b -> CatchT m a -> b Source # foldr' :: (a -> b -> b) -> b -> CatchT m a -> b Source # foldl :: (b -> a -> b) -> b -> CatchT m a -> b Source # foldl' :: (b -> a -> b) -> b -> CatchT m a -> b Source # foldr1 :: (a -> a -> a) -> CatchT m a -> a Source # foldl1 :: (a -> a -> a) -> CatchT m a -> a Source # toList :: CatchT m a -> [a] Source # null :: CatchT m a -> Bool Source # length :: CatchT m a -> Int Source # elem :: Eq a => a -> CatchT m a -> Bool Source # maximum :: Ord a => CatchT m a -> a Source # minimum :: Ord a => CatchT m a -> a Source # sum :: Num a => CatchT m a -> a Source # product :: Num a => CatchT m a -> a Source #
( Monad m, Traversable m) => Traversable ( CatchT m) Source #
Instance details Defined in Control.Monad.Catch.Pure Methods traverse :: Applicative f => (a -> f b) -> CatchT m a -> f ( CatchT m b) Source # sequenceA :: Applicative f => CatchT m (f a) -> f ( CatchT m a) Source # mapM :: Monad m0 => (a -> m0 b) -> CatchT m a -> m0 ( CatchT m b) Source # sequence :: Monad m0 => CatchT m (m0 a) -> m0 ( CatchT m a) Source #
MonadIO m => MonadIO ( CatchT m) Source #
Instance details Defined in Control.Monad.Catch.Pure Methods liftIO :: IO a -> CatchT m a Source #
Monad m => Alternative ( CatchT m) Source #
Instance details Defined in Control.Monad.Catch.Pure Methods empty :: CatchT m a Source # (<\|>) :: CatchT m a -> CatchT m a -> CatchT m a Source # some :: CatchT m a -> CatchT m [a] Source # many :: CatchT m a -> CatchT m [a] Source #
Monad m => MonadPlus ( CatchT m) Source #
Instance details Defined in Control.Monad.Catch.Pure Methods mzero :: CatchT m a Source # mplus :: CatchT m a -> CatchT m a -> CatchT m a Source #
Monad m => MonadMask ( CatchT m) Source #	Note: This instance is only valid if the underlying monad has a single exit point! For example, `IO` or `Either` would be invalid base monads, but `Reader` or `State` would be acceptable.
Instance details Defined in Control.Monad.Catch.Pure Methods mask :: (( forall a. CatchT m a -> CatchT m a) -> CatchT m b) -> CatchT m b Source # uninterruptibleMask :: (( forall a. CatchT m a -> CatchT m a) -> CatchT m b) -> CatchT m b Source # generalBracket :: CatchT m a -> (a -> ExitCase b -> CatchT m c) -> (a -> CatchT m b) -> CatchT m (b, c) Source #
Monad m => MonadCatch ( CatchT m) Source #
Instance details Defined in Control.Monad.Catch.Pure Methods catch :: Exception e => CatchT m a -> (e -> CatchT m a) -> CatchT m a Source #
Monad m => MonadThrow ( CatchT m) Source #
Instance details Defined in Control.Monad.Catch.Pure Methods throwM :: Exception e => e -> CatchT m a Source #

type Catch = CatchT Identity Source #

runCatch :: Catch a -> Either SomeException a Source #

mapCatchT :: (m ( Either SomeException a) -> n ( Either SomeException b)) -> CatchT m a -> CatchT n b Source #

Map the unwrapped computation using the given function.

runCatchT (mapCatchT f m) = f (runCatchT m)

Typeclass

The mtl style typeclass

module Control.Monad.Catch