Control.Monad.Trans.Maybe · transformers-0.6.1.2

The MaybeT monad transformer

2 declarations

newtypenewtype MaybeT (m :: Type -> Type) a

The parameterizable maybe monad, obtained by composing an arbitrary monad with the Maybe monad.

Computations are actions that may produce a value or exit.

The return function yields a computation that produces that value, while >>= sequences two subcomputations, exiting if either computation does.

Constructors

MaybeT
- runMaybeT :: m (Maybe a)

Instances25MonadTrans, Generic1, Monad, Functor, MonadFix, MonadFail, …

MonadTrans MaybeTDefined in transformers-0.6.1.2 · Control.Monad.Trans.Maybe
Functor m => Generic1 (MaybeT m)Defined in transformers-0.6.1.2 · Control.Monad.Trans.Maybe
Monad m => Monad (MaybeT m)Defined in transformers-0.6.1.2 · Control.Monad.Trans.Maybe
Functor m => Functor (MaybeT m)Defined in transformers-0.6.1.2 · Control.Monad.Trans.Maybe
MonadFix m => MonadFix (MaybeT m)Defined in transformers-0.6.1.2 · Control.Monad.Trans.Maybe
Monad m => MonadFail (MaybeT m)Defined in transformers-0.6.1.2 · Control.Monad.Trans.Maybe
(Functor m, Monad m) => Applicative (MaybeT m)Defined in transformers-0.6.1.2 · Control.Monad.Trans.Maybe
Foldable f => Foldable (MaybeT f)Defined in transformers-0.6.1.2 · Control.Monad.Trans.Maybe
Traversable f => Traversable (MaybeT f)Defined in transformers-0.6.1.2 · Control.Monad.Trans.Maybe
(Functor m, Monad m) => Alternative (MaybeT m)Defined in transformers-0.6.1.2 · Control.Monad.Trans.Maybe
Monad m => MonadPlus (MaybeT m)Defined in transformers-0.6.1.2 · Control.Monad.Trans.Maybe
MonadIO m => MonadIO (MaybeT m)Defined in transformers-0.6.1.2 · Control.Monad.Trans.Maybe
MonadZip m => MonadZip (MaybeT m)Defined in transformers-0.6.1.2 · Control.Monad.Trans.Maybe
Eq1 m => Eq1 (MaybeT m)Defined in transformers-0.6.1.2 · Control.Monad.Trans.Maybe
Ord1 m => Ord1 (MaybeT m)Defined in transformers-0.6.1.2 · Control.Monad.Trans.Maybe
Read1 m => Read1 (MaybeT m)Defined in transformers-0.6.1.2 · Control.Monad.Trans.Maybe
Show1 m => Show1 (MaybeT m)Defined in transformers-0.6.1.2 · Control.Monad.Trans.Maybe
Contravariant m => Contravariant (MaybeT m)Defined in transformers-0.6.1.2 · Control.Monad.Trans.Maybe
(Eq1 m, Eq a) => Eq (MaybeT m a)Defined in transformers-0.6.1.2 · Control.Monad.Trans.Maybe
(Ord1 m, Ord a) => Ord (MaybeT m a)Defined in transformers-0.6.1.2 · Control.Monad.Trans.Maybe
(Read1 m, Read a) => Read (MaybeT m a)Defined in transformers-0.6.1.2 · Control.Monad.Trans.Maybe
(Show1 m, Show a) => Show (MaybeT m a)Defined in transformers-0.6.1.2 · Control.Monad.Trans.Maybe
Generic (MaybeT m a)Defined in transformers-0.6.1.2 · Control.Monad.Trans.Maybe
type Rep (MaybeT m a) = D1 ('MetaData "MaybeT" "Control.Monad.Trans.Maybe" "transformers-0.6.1.2-8201" 'True) (C1 ('MetaCons "MaybeT" 'PrefixI 'True) (S1 ('MetaSel ('Just "runMaybeT") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 (m (Maybe a)))))Defined in transformers-0.6.1.2 · Control.Monad.Trans.Maybe
type Rep1 (MaybeT m) = D1 ('MetaData "MaybeT" "Control.Monad.Trans.Maybe" "transformers-0.6.1.2-8201" 'True) (C1 ('MetaCons "MaybeT" 'PrefixI 'True) (S1 ('MetaSel ('Just "runMaybeT") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (m :.: Rec1 Maybe)))Defined in transformers-0.6.1.2 · Control.Monad.Trans.Maybe

valuemapMaybeT :: (m (Maybe a) -> n (Maybe b)) -> MaybeT m a -> MaybeT n b

#

Transform the computation inside a MaybeT.

runMaybeT (mapMaybeT f m) = f (runMaybeT m)

Monad transformations

3 declarations

valuehoistMaybe :: Applicative m => Maybe b -> MaybeT m b

#

Convert a Maybe computation to MaybeT.

valuemaybeToExceptT :: Functor m => e -> MaybeT m a -> ExceptT e m a

#

Convert a MaybeT computation to ExceptT, with a default exception value.

valueexceptToMaybeT :: Functor m => ExceptT e m a -> MaybeT m a

#

Convert a ExceptT computation to MaybeT, discarding the value of any exception.

Lifting other operations

4 declarations

valueliftCallCC :: CallCC m (Maybe a) (Maybe b) -> CallCC (MaybeT m) a b

#

Lift a callCC operation to the new monad.

valueliftCatch :: Catch e m (Maybe a) -> Catch e (MaybeT m) a

#

Lift a catchE operation to the new monad.

valueliftListen :: Monad m => Listen w m (Maybe a) -> Listen w (MaybeT m) a

#

Lift a listen operation to the new monad.

valueliftPass :: Monad m => Pass w m (Maybe a) -> Pass w (MaybeT m) a

#

Lift a pass operation to the new monad.