Except - BHC Documentation

type Except e = ExceptT e Identity { } #

newtype ExceptT e m a { } #

ExceptT { runExceptT :: m (Either e a) }

The exception monad transformer.

class Monad m => MonadError e m { } #

throwError :: e -> m a

catchError :: (m a) -> (e -> m a) -> m a

Class for monads with exceptions.

runExcept :: (Except e a) -> Either e a { } #

Run an Except.

mapExcept :: ((Either e a) -> Either e' b) -> (Except e a) -> Except e' b { } #

Map the result.

withExcept :: (e -> e') -> (Except e a) -> Except e' a { } #

Transform the exception.

<*> :: { } #

>>= :: { } #

mapExceptT :: ((m (Either e a)) -> n (Either e' b)) -> (ExceptT e m a) -> ExceptT e' n b { } #

Map the inner computation.

withExceptT :: (Functor m) => (e -> e') -> (ExceptT e m a) -> ExceptT e' m a { } #

Transform the exception.

throwE :: (Monad m) => e -> ExceptT e m a { } #

O(1). Signal an error, aborting the computation.

catchE :: (Monad m) => (ExceptT e m a) -> (e -> ExceptT e' m a) -> ExceptT e' m a { } #

O(1). Handle an error by running a recovery computation.

instance Functor m => Functor (ExceptT e m) { }

instance MonadTrans (ExceptT e) { }

instance MonadIO m => MonadIO (ExceptT e m) { }

instance Monad m => MonadError e (ExceptT e m) { }