Control.Monad.Ology.Specific.MaybeT

Documentation

newtype 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

Fields

• runMaybeT :: m (Maybe a)

Instances

MonadTransCoerce MaybeT

Defined in Control.Monad.Ology.Specific.MaybeT

Methods

transCoerce :: forall (m1 :: Type -> Type) (m2 :: Type -> Type). Coercible m1 m2 => Dict (Coercible (MaybeT m1) (MaybeT m2))

MonadTransHoist MaybeT

Defined in Control.Monad.Ology.Specific.MaybeT

Methods

hoist :: forall (m1 :: Type -> Type) (m2 :: Type -> Type). (Monad m1, Monad m2) => (m1 --> m2) -> MaybeT m1 --> MaybeT m2

MonadTransTunnel MaybeT

Defined in Control.Monad.Ology.Specific.MaybeT

Associated Types

type Tunnel MaybeT :: Type -> Type

Methods

tunnel :: Monad m => ((forall (m1 :: Type -> Type) a. Monad m1 => MaybeT m1 a -> m1 (Tunnel MaybeT a)) -> m (Tunnel MaybeT r)) -> MaybeT m r

MonadTrans MaybeT

Defined in Control.Monad.Trans.Maybe

Methods

lift :: Monad m => m a -> MaybeT m a

TransConstraint MonadFail MaybeT

Defined in Control.Monad.Ology.Specific.MaybeT

Methods

hasTransConstraint :: forall (m :: Type -> Type). MonadFail m => Dict (MonadFail (MaybeT m))

TransConstraint MonadFix MaybeT

Defined in Control.Monad.Ology.Specific.MaybeT

Methods

hasTransConstraint :: forall (m :: Type -> Type). MonadFix m => Dict (MonadFix (MaybeT m))

TransConstraint MonadIO MaybeT

Defined in Control.Monad.Ology.Specific.MaybeT

Methods

hasTransConstraint :: forall (m :: Type -> Type). MonadIO m => Dict (MonadIO (MaybeT m))

TransConstraint Functor MaybeT

Defined in Control.Monad.Ology.Specific.MaybeT

Methods

hasTransConstraint :: forall (m :: Type -> Type). Functor m => Dict (Functor (MaybeT m))

TransConstraint Monad MaybeT

Defined in Control.Monad.Ology.Specific.MaybeT

Methods

hasTransConstraint :: forall (m :: Type -> Type). Monad m => Dict (Monad (MaybeT m))

TransConstraint MonadPlus MaybeT

Defined in Control.Monad.Ology.Specific.MaybeT

Methods

hasTransConstraint :: forall (m :: Type -> Type). MonadPlus m => Dict (MonadPlus (MaybeT m))

TransConstraint MonadInner MaybeT

Defined in Control.Monad.Ology.Specific.MaybeT

Methods

hasTransConstraint :: forall (m :: Type -> Type). MonadInner m => Dict (MonadInner (MaybeT m))

Monad m => MonadFail (MaybeT m)

Defined in Control.Monad.Trans.Maybe

Methods

fail :: String -> MaybeT m a

MonadFix m => MonadFix (MaybeT m)

Defined in Control.Monad.Trans.Maybe

Methods

mfix :: (a -> MaybeT m a) -> MaybeT m a

MonadIO m => MonadIO (MaybeT m)

Defined in Control.Monad.Trans.Maybe

Methods

liftIO :: IO a -> MaybeT m a

MonadZip m => MonadZip (MaybeT m)

Defined in Control.Monad.Trans.Maybe

Methods

mzip :: MaybeT m a -> MaybeT m b -> MaybeT m (a, b)

mzipWith :: (a -> b -> c) -> MaybeT m a -> MaybeT m b -> MaybeT m c

munzip :: MaybeT m (a, b) -> (MaybeT m a, MaybeT m b)

Foldable f => Foldable (MaybeT f)

Defined in Control.Monad.Trans.Maybe

Methods

fold :: Monoid m => MaybeT f m -> m

foldMap :: Monoid m => (a -> m) -> MaybeT f a -> m

foldMap' :: Monoid m => (a -> m) -> MaybeT f a -> m

foldr :: (a -> b -> b) -> b -> MaybeT f a -> b

foldr' :: (a -> b -> b) -> b -> MaybeT f a -> b

foldl :: (b -> a -> b) -> b -> MaybeT f a -> b

foldl' :: (b -> a -> b) -> b -> MaybeT f a -> b

foldr1 :: (a -> a -> a) -> MaybeT f a -> a

foldl1 :: (a -> a -> a) -> MaybeT f a -> a

toList :: MaybeT f a -> [a]

null :: MaybeT f a -> Bool

length :: MaybeT f a -> Int

elem :: Eq a => a -> MaybeT f a -> Bool

maximum :: Ord a => MaybeT f a -> a

minimum :: Ord a => MaybeT f a -> a

sum :: Num a => MaybeT f a -> a

product :: Num a => MaybeT f a -> a

Eq1 m => Eq1 (MaybeT m)

Defined in Control.Monad.Trans.Maybe

Methods

liftEq :: (a -> b -> Bool) -> MaybeT m a -> MaybeT m b -> Bool

Ord1 m => Ord1 (MaybeT m)

Defined in Control.Monad.Trans.Maybe

Methods

liftCompare :: (a -> b -> Ordering) -> MaybeT m a -> MaybeT m b -> Ordering

Read1 m => Read1 (MaybeT m)

Defined in Control.Monad.Trans.Maybe

Methods

liftReadsPrec :: (Int -> ReadS a) -> ReadS [a] -> Int -> ReadS (MaybeT m a)

liftReadList :: (Int -> ReadS a) -> ReadS [a] -> ReadS [MaybeT m a]

liftReadPrec :: ReadPrec a -> ReadPrec [a] -> ReadPrec (MaybeT m a)

liftReadListPrec :: ReadPrec a -> ReadPrec [a] -> ReadPrec [MaybeT m a]

Show1 m => Show1 (MaybeT m)

Defined in Control.Monad.Trans.Maybe

Methods

liftShowsPrec :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> Int -> MaybeT m a -> ShowS

liftShowList :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> [MaybeT m a] -> ShowS

Contravariant m => Contravariant (MaybeT m)

Defined in Control.Monad.Trans.Maybe

Methods

contramap :: (a' -> a) -> MaybeT m a -> MaybeT m a'

(>$) :: b -> MaybeT m b -> MaybeT m a

Traversable f => Traversable (MaybeT f)

Defined in Control.Monad.Trans.Maybe

Methods

traverse :: Applicative f0 => (a -> f0 b) -> MaybeT f a -> f0 (MaybeT f b)

sequenceA :: Applicative f0 => MaybeT f (f0 a) -> f0 (MaybeT f a)

mapM :: Monad m => (a -> m b) -> MaybeT f a -> m (MaybeT f b)

sequence :: Monad m => MaybeT f (m a) -> m (MaybeT f a)

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

Defined in Control.Monad.Trans.Maybe

Methods

empty :: MaybeT m a

(<|>) :: MaybeT m a -> MaybeT m a -> MaybeT m a

some :: MaybeT m a -> MaybeT m [a]

many :: MaybeT m a -> MaybeT m [a]

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

Defined in Control.Monad.Trans.Maybe

Methods

pure :: a -> MaybeT m a

(<*>) :: MaybeT m (a -> b) -> MaybeT m a -> MaybeT m b

liftA2 :: (a -> b -> c) -> MaybeT m a -> MaybeT m b -> MaybeT m c

(*>) :: MaybeT m a -> MaybeT m b -> MaybeT m b

(<*) :: MaybeT m a -> MaybeT m b -> MaybeT m a

Functor m => Functor (MaybeT m)

Defined in Control.Monad.Trans.Maybe

Methods

fmap :: (a -> b) -> MaybeT m a -> MaybeT m b

(<$) :: a -> MaybeT m b -> MaybeT m a

Monad m => Monad (MaybeT m)

Defined in Control.Monad.Trans.Maybe

Methods

(>>=) :: MaybeT m a -> (a -> MaybeT m b) -> MaybeT m b

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

return :: a -> MaybeT m a

Monad m => MonadPlus (MaybeT m)

Defined in Control.Monad.Trans.Maybe

Methods

mzero :: MaybeT m a

mplus :: MaybeT m a -> MaybeT m a -> MaybeT m a

Invariant m => Invariant (MaybeT m)

from the transformers package

Defined in Data.Functor.Invariant

Methods

invmap :: (a -> b) -> (b -> a) -> MaybeT m a -> MaybeT m b

MonadException m => MonadException (MaybeT m)

Defined in Control.Monad.Ology.Specific.MaybeT

Associated Types

type Exc (MaybeT m)

Methods

throwExc :: Exc (MaybeT m) -> MaybeT m a

catchExc :: MaybeT m a -> (Exc (MaybeT m) -> MaybeT m a) -> MaybeT m a

MonadInner m => MonadInner (MaybeT m)

Defined in Control.Monad.Ology.Specific.MaybeT

Methods

retrieveInner :: MaybeT m a -> Result (Exc (MaybeT m)) a

MonadCatch e m => MonadCatch (Maybe e) (MaybeT m)

Defined in Control.Monad.Ology.Specific.MaybeT

Methods

catch :: MaybeT m a -> (Maybe e -> MaybeT m a) -> MaybeT m a

MonadThrow e m => MonadThrow (Maybe e) (MaybeT m)

Defined in Control.Monad.Ology.Specific.MaybeT

Methods

throw :: Maybe e -> MaybeT m a

(Read1 m, Read a) => Read (MaybeT m a)

Defined in Control.Monad.Trans.Maybe

Methods

readsPrec :: Int -> ReadS (MaybeT m a)

readList :: ReadS [MaybeT m a]

readPrec :: ReadPrec (MaybeT m a)

readListPrec :: ReadPrec [MaybeT m a]

(Show1 m, Show a) => Show (MaybeT m a)

Defined in Control.Monad.Trans.Maybe

Methods

showsPrec :: Int -> MaybeT m a -> ShowS

show :: MaybeT m a -> String

showList :: [MaybeT m a] -> ShowS

(Eq1 m, Eq a) => Eq (MaybeT m a)

Defined in Control.Monad.Trans.Maybe

Methods

(==) :: MaybeT m a -> MaybeT m a -> Bool

(/=) :: MaybeT m a -> MaybeT m a -> Bool

(Ord1 m, Ord a) => Ord (MaybeT m a)

Defined in Control.Monad.Trans.Maybe

Methods

compare :: MaybeT m a -> MaybeT m a -> Ordering

(<) :: MaybeT m a -> MaybeT m a -> Bool

(<=) :: MaybeT m a -> MaybeT m a -> Bool

(>) :: MaybeT m a -> MaybeT m a -> Bool

(>=) :: MaybeT m a -> MaybeT m a -> Bool

max :: MaybeT m a -> MaybeT m a -> MaybeT m a

min :: MaybeT m a -> MaybeT m a -> MaybeT m a

type Tunnel MaybeT

Defined in Control.Monad.Ology.Specific.MaybeT

type Tunnel MaybeT = Maybe

type Exc (MaybeT m)

Defined in Control.Monad.Ology.Specific.MaybeT

type Exc (MaybeT m) = Maybe (Exc m)

maybeToExceptT :: forall (m :: Type -> Type) e a. Functor m => e -> MaybeT m a -> ExceptT e m a

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

mapMaybeT :: (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)

exceptToMaybeT :: forall (m :: Type -> Type) e a. Functor m => ExceptT e m a -> MaybeT m a

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

Orphan instances

MonadTransCoerce MaybeT

Methods

transCoerce :: forall (m1 :: Type -> Type) (m2 :: Type -> Type). Coercible m1 m2 => Dict (Coercible (MaybeT m1) (MaybeT m2))

MonadTransHoist MaybeT

Methods

hoist :: forall (m1 :: Type -> Type) (m2 :: Type -> Type). (Monad m1, Monad m2) => (m1 --> m2) -> MaybeT m1 --> MaybeT m2

MonadTransTunnel MaybeT

Associated Types

type Tunnel MaybeT :: Type -> Type

Methods

tunnel :: Monad m => ((forall (m1 :: Type -> Type) a. Monad m1 => MaybeT m1 a -> m1 (Tunnel MaybeT a)) -> m (Tunnel MaybeT r)) -> MaybeT m r

TransConstraint MonadFail MaybeT

Methods

hasTransConstraint :: forall (m :: Type -> Type). MonadFail m => Dict (MonadFail (MaybeT m))

TransConstraint MonadFix MaybeT

Methods

hasTransConstraint :: forall (m :: Type -> Type). MonadFix m => Dict (MonadFix (MaybeT m))

TransConstraint MonadIO MaybeT

Methods

hasTransConstraint :: forall (m :: Type -> Type). MonadIO m => Dict (MonadIO (MaybeT m))

TransConstraint Functor MaybeT

Methods

hasTransConstraint :: forall (m :: Type -> Type). Functor m => Dict (Functor (MaybeT m))

TransConstraint Monad MaybeT

Methods

hasTransConstraint :: forall (m :: Type -> Type). Monad m => Dict (Monad (MaybeT m))

TransConstraint MonadPlus MaybeT

Methods

hasTransConstraint :: forall (m :: Type -> Type). MonadPlus m => Dict (MonadPlus (MaybeT m))

TransConstraint MonadInner MaybeT

Methods

hasTransConstraint :: forall (m :: Type -> Type). MonadInner m => Dict (MonadInner (MaybeT m))

MonadException m => MonadException (MaybeT m)

Associated Types

type Exc (MaybeT m)

Methods

throwExc :: Exc (MaybeT m) -> MaybeT m a

catchExc :: MaybeT m a -> (Exc (MaybeT m) -> MaybeT m a) -> MaybeT m a

MonadInner m => MonadInner (MaybeT m)

Methods

retrieveInner :: MaybeT m a -> Result (Exc (MaybeT m)) a

MonadCatch e m => MonadCatch (Maybe e) (MaybeT m)

Methods

catch :: MaybeT m a -> (Maybe e -> MaybeT m a) -> MaybeT m a

MonadThrow e m => MonadThrow (Maybe e) (MaybeT m)

Methods

throw :: Maybe e -> MaybeT m a