Control.Monad.Catch.Pure

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

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!

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

Instances
Instances details
MonadTrans CatchT
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)
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 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)
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)
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)
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)
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)
Instance details

Defined in Control.Monad.Catch.Pure

Methods

mfix :: (a -> CatchT m a) -> CatchT m a Source

Monad m => MonadFail (CatchT m)
Instance details

Defined in Control.Monad.Catch.Pure

Methods

fail :: String -> CatchT m a Source

Monad m => Applicative (CatchT m)
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)
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)
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)
Instance details

Defined in Control.Monad.Catch.Pure

Methods

liftIO :: IO a -> CatchT m a Source

Monad m => Alternative (CatchT m)
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)
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)

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)
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)
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

© The University of Glasgow and others
Licensed under a BSD-style license (see top of the page).
https://downloads.haskell.org/~ghc/8.10.2/docs/html/libraries/exceptions-0.10.4/Control-Monad-Catch-Pure.html