Data.Compactable

class Compactable f  where

Compactable represents data structures which can be compacted/filtered. This is a generalization of catMaybes as a new function compact. compact has relations with Functor, Applicative, Monad, Plus, and Traversable in that we can use these classes to provide the ability to operate on a data type by eliminating intermediate Nothings. This is useful for representing the filtering out of values, or failure.

To be compactable alone, no laws must be satisfied other than the type signature.

If the data type is also a Functor the following should hold:

• Functor Identity: compact <<< map Just ≡ id

According to Kmett, (Compactable f, Functor f) is a functor from the kleisli category of Maybe to the category of Hask. Kleisli Maybe -> Hask.

If the data type is also Applicative the following should hold:

• compact <<< (pure Just <*> _) ≡ id
• applyMaybe (pure Just) ≡ id
• compact ≡ applyMaybe (pure id)

If the data type is also a Monad the following should hold:

• flip bindMaybe (pure <<< Just) ≡ id
• compact <<< (pure <<< (Just (=<<))) ≡ id
• compact ≡ flip bindMaybe pure

If the data type is also Plus the following should hold:

• compact empty ≡ empty
• compact (const Nothing <$> xs) ≡ empty

Members

• compact :: forall a. f (Maybe a) -> f a
• separate :: forall r l. f (Either l r) -> { left :: f l, right :: f r }

Instances

• Compactable Maybe
• (Monoid m) => Compactable (Either m)
• Compactable Array
• Compactable List
• (Ord k) => Compactable (Map k)

compactDefault :: forall a f. Functor f => Compactable f => f (Maybe a) -> f a

separateDefault :: forall r l f. Functor f => Compactable f => f (Either l r) -> { left :: f l, right :: f r }