Control.Monad.Trans.Maybe

Declaration of the MaybeT monad transformer.

The MaybeT monad transformer

newtype MaybeT m a

Constructors

MaybeT

Fields

runMaybeT :: m (Maybe a)

Instances

MonadTrans MaybeT

Monad m => Monad (MaybeT m)

Functor m => Functor (MaybeT m)

Monad m => MonadPlus (MaybeT m)

(Functor m, Monad m) => Applicative (MaybeT m)

(Functor m, Monad m) => Alternative (MaybeT m)

MonadIO m => MonadIO (MaybeT m)

Lifting other operations

liftCallCC :: (((Maybe a -> m (Maybe b)) -> m (Maybe a)) -> m (Maybe a)) -> ((a -> MaybeT m b) -> MaybeT m a) -> MaybeT m a

Lift a callCC operation to the new monad.

liftListen :: Monad m => (m (Maybe a) -> m (Maybe a, w)) -> MaybeT m a -> MaybeT m (a, w)

Lift a listen operation to the new monad.

liftPass :: Monad m => (m (Maybe a, w -> w) -> m (Maybe a)) -> MaybeT m (a, w -> w) -> MaybeT m a

Lift a pass operation to the new monad.