ghc-6.12.1: The GHC API Source code Contents Index

Maybes

Synopsis

module Data.Maybe data MaybeErr err val = Succeeded val | Failed err failME :: err -> MaybeErr err val isSuccess :: MaybeErr err val -> Bool fmapM_maybe :: Monad m => (a -> m b) -> Maybe a -> m (Maybe b) orElse :: Maybe a -> a -> a mapCatMaybes :: (a -> Maybe b) -> [a] -> [b] allMaybes :: [Maybe a] -> Maybe [a] firstJust :: [Maybe a] -> Maybe a expectJust :: String -> Maybe a -> a maybeToBool :: Maybe a -> Bool newtype MaybeT m a = MaybeT { runMaybeT :: m (Maybe a) }

Documentation

module Data.Maybe

data MaybeErr err val Source

Constructors Succeeded val Failed err Instances Monad (MaybeErr err)

failME :: err -> MaybeErr err val Source

isSuccess :: MaybeErr err val -> Bool Source

fmapM_maybe :: Monad m => (a -> m b) -> Maybe a -> m (Maybe b) Source

orElse :: Maybe a -> a -> a Source

mapCatMaybes :: (a -> Maybe b) -> [a] -> [b] Source

allMaybes :: [Maybe a] -> Maybe [a] Source

Collects a list of Justs into a single Just, returning Nothing if there are any Nothings.

firstJust :: [Maybe a] -> Maybe a Source

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

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

maybeToBool :: Maybe a -> Bool Source

newtype MaybeT m a Source

Constructors MaybeT runMaybeT :: m (Maybe a) Instances Monad m => Monad (MaybeT m) Functor m => Functor (MaybeT m)

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