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{-# LANGUAGE DerivingStrategies #-}
{-# LANGUAGE DerivingVia #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE PolyKinds #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE StandaloneDeriving #-}
module DerivingVia2 where
import Control.Applicative
import Data.Functor.Compose
import Data.Proxy
import Data.Semigroup
newtype App (f :: * -> *) a = App (f a)
deriving newtype
(Functor, Applicative)
instance (Applicative f, Semigroup a) => Semigroup (App f a) where
(<>) = liftA2 (<>)
deriving via (App (Compose (f :: * -> *) g) a)
instance (Applicative f, Applicative g, Semigroup a)
=> Semigroup (Compose f g a)
class C (a :: k -> *)
instance C Proxy
newtype MyProxy a = MyProxy (Proxy a)
deriving via (Proxy :: * -> *) instance C MyProxy
class Z a b
data T a
data X1 a
data X2 a
data X3 a
deriving via (forall a. T a) instance Z a (X1 b)
deriving via (T a) instance forall b. Z a (X2 b)
deriving via (forall a. T a) instance forall b. Z a (X3 b)
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