viacodensity.hs

{-# Language KindSignatures, RankNTypes, DerivingVia #-}

newtype Foo i o m r = Foo (Await i m r -> Yield o m r -> m r)

newtype Pipe i o m a = Pipe (forall xx. (a -> Await i m xx -> Yield o m xx -> m xx) -> (Await i m xx -> Yield o m xx -> m xx))
  deriving (Functor, Applicative, Monad)
  via Codensity (Foo i o m)

-- Fluff --

data Await i (m :: * -> *) r
data Yield i (m :: * -> *) r

instance Functor (Codensity m)
instance Applicative (Codensity m)
instance Monad (Codensity m)

newtype Codensity m a = CD (forall r. (a -> m r) -> m r)

main = main