Control.Monad.Trans.List

The ListT monad transformer, adding backtracking to a given monad, which must be commutative.

The ListT monad transformer

newtype ListT m a

Parameterizable list monad, with an inner monad.

Note: this does not yield a monad unless the argument monad is commutative.

Constructors

ListT

Fields

runListT :: m [a]

Instances

MonadTrans ListT

Monad m => Monad (ListT m)

Functor m => Functor (ListT m)

Monad m => MonadPlus (ListT m)

Applicative m => Applicative (ListT m)

Applicative m => Alternative (ListT m)

MonadIO m => MonadIO (ListT m)

mapListT :: (m [a] -> n [b]) -> ListT m a -> ListT n b

Map between ListT computations.

• runListT (mapListT f m) = f (runListT m)

Lifting other operations

liftCallCC :: ((([a] -> m [b]) -> m [a]) -> m [a]) -> ((a -> ListT m b) -> ListT m a) -> ListT m a

Lift a callCC operation to the new monad.

liftCatch :: (m [a] -> (e -> m [a]) -> m [a]) -> ListT m a -> (e -> ListT m a) -> ListT m a

Lift a catchError operation to the new monad.