Maybe -package +transformers

module Control.Monad.Trans.Maybe
transformers Control.Monad.Trans.Maybe
The MaybeT monad transformer adds the ability to fail to a monad. A sequence of actions succeeds, producing a value, only if all the actions in the sequence are successful. If one fails, the rest of the sequence is skipped and the composite action fails. For a variant allowing a range of error values, see Control.Monad.Trans.Error.
MaybeT :: m (Maybe a) -> MaybeT m a
transformers Control.Monad.Trans.Maybe
newtype MaybeT m a
transformers Control.Monad.Trans.Maybe
The parameterizable maybe monad, obtained by composing an arbitrary monad with the Maybe monad. Computations are actions that may produce a value or fail. The return function yields a successful computation, while >>= sequences two subcomputations, failing on the first error.
mapMaybeT :: (m (Maybe a) -> n (Maybe b)) -> MaybeT m a -> MaybeT n b
transformers Control.Monad.Trans.Maybe
Transform the computation inside a MaybeT. *  (mapMaybeT f m) = f (runMaybeT >  
runMaybeT :: MaybeT m a -> m (Maybe a)
transformers Control.Monad.Trans.Maybe