AlternativeExtra.hs

{- |
Utilities extending Control.Applicative
-}
module Control.AlternativeExtra (
  mmany,
  msome,
  manyWith,
  someWith,
  ($<)
  )where

import Control.Applicative

-- | Many generalization for Monoid instances
mmany :: (Alternative a, Monoid m) => a m -> a m
mmany f = foldl mappend mempty <$> many f

-- | Some generatlization for Monoid instances
msome :: (Alternative a, Monoid m) => a m -> a m
msome f = foldl mappend mempty <$> some f

-- | Function application with lifted parameter
($<) :: Applicative m => m (a -> b) -> a -> m b
($<) f a = f <*> pure a

{- |

Utility for casting bare values into a Monoid in mmany.

For example, the function:

>  let sumMany = manyWith Sum getSum

will sum the results of many.
-}
manyWith :: (Alternative a, Monoid m) => (v -> m) -> (m -> v) -> a v -> a v
manyWith toMonoid fromMonoid f = fromMonoid <$> (mmany $ toMonoid <$> f)

{- |

Utility for casting bare values into a Monoid in msome.

For example, the function:

> let sumSome = someWith Sum getSum

will sum the results of some.
-}
someWith :: (Alternative a, Monoid m) => (v -> m) -> (m -> v) -> a v -> a v
someWith toMonoid fromMonoid f = fromMonoid <$> (msome $ toMonoid <$> f)