Safe Haskell	Safe
Language	Haskell2010

Maybes

Synopsis

Documentation

module Data.Maybe

data MaybeErr err val Source

Constructors

Succeeded val
Failed err

Instances

Monad (MaybeErr err)
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 fail :: String -> MaybeErr err a Source
Functor (MaybeErr err)
Methods fmap :: (a -> b) -> MaybeErr err a -> MaybeErr err b Source (<$) :: a -> MaybeErr err b -> MaybeErr err a Source
Applicative (MaybeErr err)
Methods pure :: a -> MaybeErr err a Source (<>) :: MaybeErr err (a -> b) -> MaybeErr err a -> MaybeErr err b Source (>) :: MaybeErr err a -> MaybeErr err b -> MaybeErr err b Source (<*) :: MaybeErr err a -> MaybeErr err b -> 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 :: [Maybe a] -> Maybe a Source

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

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

expectJust :: String -> Maybe a -> a Source

newtype MaybeT m a :: (TYPE Lifted -> TYPE Lifted) -> TYPE Lifted -> TYPE Lifted 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

MonadTrans MaybeT
Methods lift :: Monad m => m a -> MaybeT m a Source
Monad m => Monad (MaybeT m)
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 fail :: String -> MaybeT m a Source
Functor m => Functor (MaybeT m)
Methods fmap :: (a -> b) -> MaybeT m a -> MaybeT m b Source (<$) :: a -> MaybeT m b -> MaybeT m a Source
MonadFix m => MonadFix (MaybeT m)
Methods mfix :: (a -> MaybeT m a) -> MaybeT m a Source
Monad m => MonadFail (MaybeT m)
Methods fail :: String -> MaybeT m a Source
(Functor m, Monad m) => Applicative (MaybeT m)
Methods pure :: a -> MaybeT m a Source (<>) :: MaybeT m (a -> b) -> MaybeT m a -> MaybeT m b Source (>) :: MaybeT m a -> MaybeT m b -> MaybeT m b Source (<*) :: MaybeT m a -> MaybeT m b -> MaybeT m a Source
Foldable f => Foldable (MaybeT f)
Methods fold :: Monoid m => MaybeT f m -> 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
Traversable f => Traversable (MaybeT f)
Methods traverse :: Applicative f => (a -> f b) -> MaybeT f a -> f (MaybeT f b) Source sequenceA :: Applicative f => MaybeT f (f a) -> f (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
Eq1 m => Eq1 (MaybeT m)
Methods liftEq :: (a -> b -> Bool) -> MaybeT m a -> MaybeT m b -> Bool Source
Ord1 m => Ord1 (MaybeT m)
Methods liftCompare :: (a -> b -> Ordering) -> MaybeT m a -> MaybeT m b -> Ordering Source
Read1 m => Read1 (MaybeT m)
Methods liftReadsPrec :: (Int -> ReadS a) -> ReadS [a] -> Int -> ReadS (MaybeT m a) Source liftReadList :: (Int -> ReadS a) -> ReadS [a] -> ReadS [MaybeT m a] Source
Show1 m => Show1 (MaybeT m)
Methods liftShowsPrec :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> Int -> MaybeT m a -> ShowS Source liftShowList :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> [MaybeT m a] -> ShowS Source
MonadIO m => MonadIO (MaybeT m)
Methods liftIO :: IO a -> MaybeT m a Source
MonadZip m => MonadZip (MaybeT m)
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
(Functor m, Monad m) => Alternative (MaybeT m)
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
Monad m => MonadPlus (MaybeT m)
Methods mzero :: MaybeT m a Source mplus :: MaybeT m a -> MaybeT m a -> MaybeT m a Source
(Monad m, HasDynFlags m) => HasDynFlags (MaybeT m)
Methods getDynFlags :: MaybeT m DynFlags Source
(Eq1 m, Eq a) => Eq (MaybeT m a)
Methods (==) :: MaybeT m a -> MaybeT m a -> Bool (/=) :: MaybeT m a -> MaybeT m a -> Bool
(Ord1 m, Ord a) => Ord (MaybeT m a)
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
(Read1 m, Read a) => Read (MaybeT m a)
Methods readsPrec :: Int -> ReadS (MaybeT m a) Source readList :: ReadS [MaybeT m a] Source readPrec :: ReadPrec (MaybeT m a) Source readListPrec :: ReadPrec [MaybeT m a] Source
(Show1 m, Show a) => Show (MaybeT m a)
Methods showsPrec :: Int -> MaybeT m a -> ShowS Source show :: MaybeT m a -> String Source showList :: [MaybeT m a] -> ShowS Source

liftMaybeT :: Monad m => m a -> MaybeT m a Source