Control.Monad.Trans.Either

This monad transformer extends Control.Monad.Trans.Except with a more familar Either naming.

Control.Monad.Trans.Either

type EitherT = ExceptT

Type alias for ExceptT

newEitherT :: m (Either x a) -> EitherT x m a

Constructor for computations in the either monad. (The inverse of runEitherT).

pattern EitherT :: m (Either x a) -> ExceptT x m a

runEitherT :: EitherT x m a -> m (Either x a)

Extractor for computations in the either monad. (The inverse of newEitherT).

eitherT :: Monad m => (x -> m b) -> (a -> m b) -> EitherT x m a -> m b

left :: Monad m => x -> EitherT x m a

Constructor for left computations.

right :: Monad m => a -> EitherT x m a

Constructor for right computations.

mapEitherT :: (m (Either x a) -> n (Either y b)) -> EitherT x m a -> EitherT y n b

hoistEither :: Monad m => Either x a -> EitherT x m a

Hoist an Either into an "EitherT m"

bimapEitherT :: Functor m => (x -> y) -> (a -> b) -> EitherT x m a -> EitherT y m b

Map the unwrapped computation using the given function.

Extensions

firstEitherT :: Functor m => (x -> y) -> EitherT x m a -> EitherT y m a

Map the Left unwrapped computation using the given function.

secondEitherT :: Functor m => (a -> b) -> EitherT x m a -> EitherT x m b

Map the Right unwrapped computation using the given function.

hoistMaybe :: Monad m => x -> Maybe a -> EitherT x m a

Hoist a 'Maybe a' into a 'Right a'

hoistEitherT :: (forall b. m b -> n b) -> EitherT x m a -> EitherT x n a

Hoist