-- Adding another type class on Entity, but unable to put `GetMessage a`

{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE UndecidableSuperClasses #-}


import Data.Kind

main :: IO ()
main = pure ()

-- "Library"

-- making `a` the second variable
data Entity (c :: Type -> Constraint) = forall a. (c a) => MkEntity a

class (c1 a, c2 a) => (c1 & c2) a
instance (c1 a, c2 a) => (c1 & c2) a

class HasDataID a where
  getDependencies :: a -> Entity HasDataID -- ??

instance HasDataID (Entity HasDataID) where
  getDependencies (MkEntity x) = getDependencies x



-- "User"

data Foo = Foo Bar

data Bar = Bar

instance HasDataID Foo where
  getDependencies (Foo bar) = MkEntity bar

instance HasDataID Bar where
  getDependencies bar = MkEntity bar



class GetMessage a where
  getMessage :: Int -> a -> String

instance GetMessage (Entity GetMessage) where
  getMessage int (MkEntity x) = getMessage int x


bla :: Entity (HasDataID & GetMessage) -> Entity (HasDataID & GetMessage)
bla e = getDependencies e