{-# Language TypeFamilies, DataKinds, TypeOperators, ConstraintKinds, ExistentialQuantification, KindSignatures, UndecidableInstances #-}

module Help where

import Data.Kind

main :: IO ()
main = pure ()

data Entity (cs :: [Type -> Constraint]) = forall a. All cs a => MkEntity a

type family All (cs :: [Type -> Constraint]) (a :: Type) :: Constraint where
  All (c ': cs) a = (c a, All cs a)
  All '[]       a = ()

class Op1 a where
  op1 :: a -> Entity [Op1]

class Op2 a where
  op2 :: a -> Char

data Foo = Foo Bar

data Bar = Bar

-- data Foo = Foo { fooInt :: Int, fooChar :: Char }

instance Op1 Foo where
  op1 (Foo bar) = MkEntity bar

instance Op1 Bar where
  op1 bar = MkEntity bar
-- instance Op2 Foo where op2 = fooChar

instance Op2 Bar where
  op2 bar = 'A'

example :: Entity [Op1]
example = MkEntity Bar