Data.Filtrable

Documentation

class Functor f => Filtrable f where

Laws:

• mapMaybe Just = id

• mapMaybe f = catMaybes ∘ fmap f

• catMaybes = mapMaybe id

• filter f = mapMaybe (\ x -> bool Nothing (Just x) (f x))

• mapMaybe g . mapMaybe f = mapMaybe (g <=< f)

Laws if Foldable f:

• foldMap g . filter f = foldMap (\ x -> bool mempty (g x) (f x))

Minimal complete definition

mapMaybe | catMaybes

Methods

mapMaybe :: (a -> Maybe b) -> f a -> f b

catMaybes :: f (Maybe a) -> f a

filter :: (a -> Bool) -> f a -> f a

Instances

Filtrable []

Filtrable Maybe

Filtrable (Const a)

Filtrable (Proxy *)

mapMaybeA :: (Filtrable f, Traversable f, Applicative p) => (a -> p (Maybe b)) -> f a -> p (f b)

filterA :: (Filtrable f, Traversable f, Applicative p) => (a -> p Bool) -> f a -> p (f a)