ghc-7.10.2: The GHC API

Safe HaskellSafe
LanguageHaskell2010

Maybes

Synopsis

Documentation

module Data.Maybe

data MaybeErr err val

Constructors

Succeeded val 
Failed err 

Instances

failME :: err -> MaybeErr err val

isSuccess :: MaybeErr err val -> Bool

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

Flipped version of fromMaybe, useful for chaining.

firstJust :: Maybe a -> Maybe a -> Maybe a

firstJusts :: [Maybe a] -> Maybe a

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 ()

expectJust :: String -> Maybe a -> a

newtype MaybeT m a

Constructors

MaybeT 

Fields

runMaybeT :: m (Maybe a)
 

Instances

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