J Applicative

japp.hs

{-# LANGUAGE FlexibleInstances #-}
import Control.Applicative

newtype J a = J { runJ :: a }

instance (Applicative f, Num n) => Num (J(f n)) where
    (+) = (J .) . liftA2 (+) `on` runJ
    (-) = (J .) . liftA2 (-) `on` runJ
    (*) = (J .) . liftA2 (*) `on` runJ
    abs = J . fmap abs . runJ
    signum = J . fmap signum . runJ
    fromInteger = J . pure . fromIntegral
    
runJ $ J[1..5] + J[2]
[3,4,5,6,7]

getZipList.runJ $ J(ZipList[1..5]) + J(ZipList[2..6])
[3,5,7,9,11]

runJ (J length + J sum) $ [1..10]
65