Safe Haskell	None
Language	Haskell2010

GHC.Data.Maybe

Contents

MaybeT

Synopsis

module Data.Maybe
data MaybeErr err val
- = Succeeded val
- | Failed err
failME :: err -> MaybeErr err val
isSuccess :: MaybeErr err val -> Bool
orElse :: Maybe a -> a -> a
firstJust :: Maybe a -> Maybe a -> Maybe a
firstJusts :: Foldable f => f (Maybe a) -> Maybe a
firstJustsM :: (Monad m, Foldable f) => f (m (Maybe a)) -> m (Maybe a)
whenIsJust :: Monad m => Maybe a -> (a -> m ()) -> m ()
expectJust :: HasDebugCallStack => String -> Maybe a -> a
rightToMaybe :: Either a b -> Maybe b
newtype MaybeT (m :: Type -> Type) a = MaybeT {
- runMaybeT :: m (Maybe a)
}
liftMaybeT :: Monad m => m a -> MaybeT m a
tryMaybeT :: IO a -> MaybeT IO a

Documentation

module Data.Maybe

data MaybeErr err val Source #

Constructors

Succeeded val
Failed err

Instances

Instances details

Applicative (MaybeErr err) Source #
Instance details Defined in GHC.Data.Maybe Methods pure :: a -> MaybeErr err a Source # (<>) :: MaybeErr err (a -> b) -> MaybeErr err a -> MaybeErr err b Source # liftA2 :: (a -> b -> c) -> MaybeErr err a -> MaybeErr err b -> MaybeErr err c Source # (>) :: MaybeErr err a -> MaybeErr err b -> MaybeErr err b Source # (<*) :: MaybeErr err a -> MaybeErr err b -> MaybeErr err a Source #
Functor (MaybeErr err) Source #
Instance details Defined in GHC.Data.Maybe Methods fmap :: (a -> b) -> MaybeErr err a -> MaybeErr err b Source # (<$) :: a -> MaybeErr err b -> MaybeErr err a Source #
Monad (MaybeErr err) Source #
Instance details Defined in GHC.Data.Maybe Methods (>>=) :: MaybeErr err a -> (a -> MaybeErr err b) -> MaybeErr err b Source # (>>) :: MaybeErr err a -> MaybeErr err b -> MaybeErr err b Source # return :: a -> MaybeErr err a Source #

failME :: err -> MaybeErr err val Source #

isSuccess :: MaybeErr err val -> Bool Source #

orElse :: Maybe a -> a -> a infixr 4 Source #

Flipped version of fromMaybe, useful for chaining.

firstJust :: Maybe a -> Maybe a -> Maybe a Source #

firstJusts :: Foldable f => f (Maybe a) -> Maybe a Source #

Takes a list of Maybes and returns the first Just if there is one, or Nothing otherwise.

firstJustsM :: (Monad m, Foldable f) => f (m (Maybe a)) -> m (Maybe a) Source #

Takes computations returnings Maybes; tries each one in order. The first one to return a Just wins. Returns Nothing if all computations return Nothing.

whenIsJust :: Monad m => Maybe a -> (a -> m ()) -> m () Source #

expectJust :: HasDebugCallStack => String -> Maybe a -> a Source #

rightToMaybe :: Either a b -> Maybe b Source #

MaybeT

newtype MaybeT (m :: Type -> Type) a Source #

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

Instances details

MonadTrans MaybeT

Instance details

Defined in Control.Monad.Trans.Maybe

Methods

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

Functor m => Generic1 (MaybeT m :: Type -> Type)

Instance details

Defined in Control.Monad.Trans.Maybe

Associated Types

type Rep1 (MaybeT m :: Type -> Type)
Instance details Defined in Control.Monad.Trans.Maybe type Rep1 (MaybeT m :: Type -> Type) = D1 ('MetaData "MaybeT" "Control.Monad.Trans.Maybe" "transformers-0.6.1.0-00ab" 'True) (C1 ('MetaCons "MaybeT" 'PrefixI 'True) (S1 ('MetaSel ('Just "runMaybeT") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (m :.: Rec1 Maybe)))

Methods

from1 :: MaybeT m a -> Rep1 (MaybeT m) a Source #

to1 :: Rep1 (MaybeT m) a -> MaybeT m a Source #

Monad m => MonadFail (MaybeT m)

Instance details

Defined in Control.Monad.Trans.Maybe

Methods

fail :: String -> MaybeT m a Source #

MonadFix m => MonadFix (MaybeT m)

Instance details

Defined in Control.Monad.Trans.Maybe

Methods

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

MonadIO m => MonadIO (MaybeT m)

Instance details

Defined in Control.Monad.Trans.Maybe

Methods

liftIO :: IO a -> MaybeT m a Source #

MonadZip m => MonadZip (MaybeT m)

Instance details

Defined in Control.Monad.Trans.Maybe

Methods

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

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

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

Foldable f => Foldable (MaybeT f)

Instance details

Defined in Control.Monad.Trans.Maybe

Methods

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

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

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

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

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

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

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

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

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

toList :: MaybeT f a -> [a] Source #

null :: MaybeT f a -> Bool Source #

length :: MaybeT f a -> Int Source #

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

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

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

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

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

Eq1 m => Eq1 (MaybeT m)

Instance details

Defined in Control.Monad.Trans.Maybe

Methods

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

Ord1 m => Ord1 (MaybeT m)

Instance details

Defined in Control.Monad.Trans.Maybe

Methods

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

Read1 m => Read1 (MaybeT m)

Instance details

Defined in Control.Monad.Trans.Maybe

Methods

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

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

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

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

Show1 m => Show1 (MaybeT m)

Instance details

Defined in Control.Monad.Trans.Maybe

Methods

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

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

Contravariant m => Contravariant (MaybeT m)

Instance details

Defined in Control.Monad.Trans.Maybe

Methods

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

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

Traversable f => Traversable (MaybeT f)

Instance details

Defined in Control.Monad.Trans.Maybe

Methods

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

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

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

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

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

Instance details

Defined in Control.Monad.Trans.Maybe

Methods

empty :: MaybeT m a Source #

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

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

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

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

Instance details

Defined in Control.Monad.Trans.Maybe

Methods

pure :: a -> MaybeT m a Source #

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

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

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

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

Functor m => Functor (MaybeT m)

Instance details

Defined in Control.Monad.Trans.Maybe

Methods

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

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

Monad m => Monad (MaybeT m)

Instance details

Defined in Control.Monad.Trans.Maybe

Methods

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

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

return :: a -> MaybeT m a Source #

Monad m => MonadPlus (MaybeT m)

Instance details

Defined in Control.Monad.Trans.Maybe

Methods

mzero :: MaybeT m a Source #

mplus :: MaybeT m a -> MaybeT m a -> MaybeT m a Source #

MonadCatch m => MonadCatch (MaybeT m)

Catches exceptions from the base monad.

Instance details

Defined in Control.Monad.Catch

Methods

catch :: (HasCallStack, Exception e) => MaybeT m a -> (e -> MaybeT m a) -> MaybeT m a Source #

MonadMask m => MonadMask (MaybeT m)

Since: exceptions-0.10.0

Instance details

Defined in Control.Monad.Catch

Methods

mask :: HasCallStack => ((forall a. MaybeT m a -> MaybeT m a) -> MaybeT m b) -> MaybeT m b Source #

uninterruptibleMask :: HasCallStack => ((forall a. MaybeT m a -> MaybeT m a) -> MaybeT m b) -> MaybeT m b Source #

generalBracket :: HasCallStack => MaybeT m a -> (a -> ExitCase b -> MaybeT m c) -> (a -> MaybeT m b) -> MaybeT m (b, c) Source #

MonadThrow m => MonadThrow (MaybeT m)

Throws exceptions into the base monad.

Instance details

Defined in Control.Monad.Catch

Methods

throwM :: (HasCallStack, Exception e) => e -> MaybeT m a Source #

(Monad m, HasDynFlags m) => HasDynFlags (MaybeT m) Source #

Instance details

Defined in GHC.Driver.DynFlags

Methods

getDynFlags :: MaybeT m DynFlags Source #

Generic (MaybeT m a)

Instance details

Defined in Control.Monad.Trans.Maybe

Associated Types

type Rep (MaybeT m a)
Instance details Defined in Control.Monad.Trans.Maybe type Rep (MaybeT m a) = D1 ('MetaData "MaybeT" "Control.Monad.Trans.Maybe" "transformers-0.6.1.0-00ab" 'True) (C1 ('MetaCons "MaybeT" 'PrefixI 'True) (S1 ('MetaSel ('Just "runMaybeT") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 (m (Maybe a)))))