Just an experiment to have something like this:
class Newtype t where
type Un t :: Type
un :: t -> Un t
wrap :: Un t -> t
-- un . wrap = id
-- wrap . un = id
instance Newtype (Identity a) where
type Un (Identity a) = a
un = runIdentity
wrap = Identity
newtype Bar = Bar Int
deriving Newtype via (Identity Int)And then we can write functions like these:
under :: Newtype t => (Un t -> Un t) -> t -> t
under f = wrap . f . un
Just an experiment to have something like this:
And then we can write functions like these: