never executed always true always false

    1 module Data.Coapplicative (Coapplicative(..)) where
    2 
    3 import Data.Functor.Compose
    4 import Data.Functor.Identity
    5 
    6 
    7 class Functor f => Coapplicative f where
    8     extract :: f a -> a
    9 
   10 instance Coapplicative ((,) x) where
   11     extract (_, a) = a
   12     {-# INLINE extract #-}
   13 
   14 instance Coapplicative Identity where
   15     extract = runIdentity
   16     {-# INLINE extract #-}
   17 
   18 instance (Coapplicative a, Coapplicative b) => Coapplicative (Compose a b) where
   19     extract = extract . extract . getCompose
   20     {-# INLINE extract #-}