I see this as being generally (as in, to the users of Haskell as a whole) useful:

newtype Ap f a = Ap { getAp :: f a }

  deriving (Applicative, Eq, Foldable, Functor, Generic, Generic1

                ,Monad, Ord, Read, Show, Traversable)

Some hand-written instances:

instance (Applicative f, Semigroup a) => Semigroup (Ap f a) where

  (Ap x) <> (Ap y) = Ap $ liftA2 (<>) x y

instance (Applicative f, Monoid a) => Monoid (Ap f a) where

  mempty = Ap $ pure mempty

_______________________________________________
Libraries mailing list
Libraries@haskell.org
http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries