Copyright  (C) Edward Kmett 20132015 (c) Google Inc. 2012 

License  BSDstyle (see the file LICENSE) 
Maintainer  Edward Kmett <ekmett@gmail.com> 
Stability  experimental 
Portability  nonportable 
Safe Haskell  Trustworthy 
Language  Haskell2010 
Synopsis
 newtype CatchT (m :: Type > Type) 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 :: Type > Type) 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!
CatchT  

Instances
mapCatchT :: (m (Either SomeException a) > n (Either SomeException b)) > CatchT m a > CatchT n b Source #
Typeclass
The mtl style typeclass
module Control.Monad.Catch