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 #

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

MonadTrans CatchT #
Instance details Defined in Control.Monad.Catch.Pure Methods lift :: Monad m => m a -> CatchT m a #
MonadRWS r w s m => MonadRWS r w s (CatchT m) #
Instance details Defined in Control.Monad.Catch.Pure
MonadWriter w m => MonadWriter w (CatchT m) #
Instance details Defined in Control.Monad.Catch.Pure Methods writer :: (a, w) -> CatchT m a # tell :: w -> CatchT m () # listen :: CatchT m a -> CatchT m (a, w) # pass :: CatchT m (a, w -> w) -> CatchT m a #
MonadState s m => MonadState s (CatchT m) #
Instance details Defined in Control.Monad.Catch.Pure Methods get :: CatchT m s # put :: s -> CatchT m () # state :: (s -> (a, s)) -> CatchT m a #
MonadReader e m => MonadReader e (CatchT m) #
Instance details Defined in Control.Monad.Catch.Pure Methods ask :: CatchT m e # local :: (e -> e) -> CatchT m a -> CatchT m a # reader :: (e -> a) -> CatchT m a #
Monad m => Monad (CatchT m) #
Instance details Defined in Control.Monad.Catch.Pure Methods (>>=) :: CatchT m a -> (a -> CatchT m b) -> CatchT m b # (>>) :: CatchT m a -> CatchT m b -> CatchT m b # return :: a -> CatchT m a # fail :: String -> CatchT m a #
Monad m => Functor (CatchT m) #
Instance details Defined in Control.Monad.Catch.Pure Methods fmap :: (a -> b) -> CatchT m a -> CatchT m b # (<$) :: a -> CatchT m b -> CatchT m a #
MonadFix m => MonadFix (CatchT m) #
Instance details Defined in Control.Monad.Catch.Pure Methods mfix :: (a -> CatchT m a) -> CatchT m a #
Monad m => Applicative (CatchT m) #
Instance details Defined in Control.Monad.Catch.Pure Methods pure :: a -> CatchT m a # (<>) :: CatchT m (a -> b) -> CatchT m a -> CatchT m b # liftA2 :: (a -> b -> c) -> CatchT m a -> CatchT m b -> CatchT m c # (>) :: CatchT m a -> CatchT m b -> CatchT m b # (<*) :: CatchT m a -> CatchT m b -> CatchT m a #
Foldable m => Foldable (CatchT m) #
Instance details Defined in Control.Monad.Catch.Pure Methods fold :: Monoid m0 => CatchT m m0 -> m0 # foldMap :: Monoid m0 => (a -> m0) -> CatchT m a -> m0 # foldr :: (a -> b -> b) -> b -> CatchT m a -> b # foldr' :: (a -> b -> b) -> b -> CatchT m a -> b # foldl :: (b -> a -> b) -> b -> CatchT m a -> b # foldl' :: (b -> a -> b) -> b -> CatchT m a -> b # foldr1 :: (a -> a -> a) -> CatchT m a -> a # foldl1 :: (a -> a -> a) -> CatchT m a -> a # toList :: CatchT m a -> [a] # null :: CatchT m a -> Bool # length :: CatchT m a -> Int # elem :: Eq a => a -> CatchT m a -> Bool # maximum :: Ord a => CatchT m a -> a # minimum :: Ord a => CatchT m a -> a # sum :: Num a => CatchT m a -> a # product :: Num a => CatchT m a -> a #
(Monad m, Traversable m) => Traversable (CatchT m) #
Instance details Defined in Control.Monad.Catch.Pure Methods traverse :: Applicative f => (a -> f b) -> CatchT m a -> f (CatchT m b) # sequenceA :: Applicative f => CatchT m (f a) -> f (CatchT m a) # mapM :: Monad m0 => (a -> m0 b) -> CatchT m a -> m0 (CatchT m b) # sequence :: Monad m0 => CatchT m (m0 a) -> m0 (CatchT m a) #
MonadIO m => MonadIO (CatchT m) #
Instance details Defined in Control.Monad.Catch.Pure Methods liftIO :: IO a -> CatchT m a #
Monad m => Alternative (CatchT m) #
Instance details Defined in Control.Monad.Catch.Pure Methods empty :: CatchT m a # (<\|>) :: CatchT m a -> CatchT m a -> CatchT m a # some :: CatchT m a -> CatchT m [a] # many :: CatchT m a -> CatchT m [a] #
Monad m => MonadPlus (CatchT m) #
Instance details Defined in Control.Monad.Catch.Pure Methods mzero :: CatchT m a # mplus :: CatchT m a -> CatchT m a -> CatchT m a #
Monad m => MonadMask (CatchT m) #	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 # uninterruptibleMask :: ((forall a. CatchT m a -> CatchT m a) -> CatchT m b) -> CatchT m b # generalBracket :: CatchT m a -> (a -> ExitCase b -> CatchT m c) -> (a -> CatchT m b) -> CatchT m (b, c) #
Monad m => MonadCatch (CatchT m) #
Instance details Defined in Control.Monad.Catch.Pure Methods catch :: Exception e => CatchT m a -> (e -> CatchT m a) -> CatchT m a #
Monad m => MonadThrow (CatchT m) #
Instance details Defined in Control.Monad.Catch.Pure Methods throwM :: Exception e => e -> CatchT m 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 #

Map the unwrapped computation using the given function.

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

Typeclass

The mtl style typeclass

module Control.Monad.Catch