Control.Monad.Maybe

Definitions

data MaybeT : (Type -> Type) -> Type -> Type

  A monad transformer extending an inner monad with the ability to not return
  a result.
  
  Sequenced actions produce a result only if both actions return a result.
  
  `MaybeT m a` is equivalent to `EitherT () m a`, that is, an computation
  that can only throw a single, information-less exception.

Totality: total
Visibility: public export
Constructor: 

MkMaybeT : m (Maybe a) -> MaybeT m a

Hints:

Monad m => Alternative (MaybeT m)

Applicative m => Applicative (MaybeT m)

Eq (m (Maybe a)) => Eq (MaybeT m a)

Foldable m => Foldable (MaybeT m)

Functor m => Functor (MaybeT m)

HasIO m => HasIO (MaybeT m)

Monad m => Monad (MaybeT m)

Monad m => MonadError () (MaybeT m)

MonadError e m => MonadError e (MaybeT m)

MonadTrans MaybeT

Monad m => Monoid (MaybeT m a)

Ord (m (Maybe a)) => Ord (MaybeT m a)

Monad m => Semigroup (MaybeT m a)

Show (m (Maybe a)) => Show (MaybeT m a)

Traversable m => Traversable (MaybeT m)

runMaybeT : MaybeT m a -> m (Maybe a)

  Unwrap a `MaybeT` computation.

Totality: total
Visibility: public export

isNothingT : Functor m => MaybeT m a -> m Bool

  Check if a monadic computation returns a result. This returns `False` if
  the computation returns a result, and `True` otherwise.
  
  This is a version of `isNothing` lifted to work with `MaybeT`.

Totality: total
Visibility: public export

isJustT : Functor m => MaybeT m a -> m Bool

  Check if a monadic computation returns a result. This returns `True` if
  the computation returns a result, and `False` otherwise.
  
  This is a version of `isJust` lifted to work with `MaybeT`.

Totality: total
Visibility: public export

maybeT : Monad m => m b -> (a -> m b) -> MaybeT m a -> m b

  Run a `MaybeT` computation, handling the case of a result or no result
  separately.
  
  This is a version of `maybe` lifted to work with `MaybeT`.

Totality: total
Visibility: public export

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

  Run a `MaybeT` computation providing a default value.
  
  This is a version of `fromMaybe` lifted to work with `MaybeT`.

Totality: total
Visibility: public export

toMaybeT : Functor m => Bool -> m a -> MaybeT m a

  Return a value if a condition is met, or else no value. The condition
  only affects whether the `Maybe` produces a value; the effect is run
  either way.
  
  This is a version of `toMaybe` lifted to work with `MaybeT`.

Totality: total
Visibility: public export

mapMaybeT : (m (Maybe a) -> n (Maybe a')) -> MaybeT m a -> MaybeT n a'

  Map over the underlying computation.

Totality: total
Visibility: public export

just : Applicative m => a -> MaybeT m a

  A version of `Just` lifted to work with `MaybeT`.
  
  This is equivalent to `pure`.

Totality: total
Visibility: public export

nothing : Applicative m => MaybeT m a

  A version of `Nothing` lifted to work with `MaybeT`.
  
  This is equivalent to `throwE ()`.

Totality: total
Visibility: public export