{-# LANGUAGE GADTs #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE KindSignatures #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE RankNTypes #-}

import GHC.Exts (Constraint)

class Function f where
  type Constraints f a :: Constraint
  type instance Constraints f a = ()
  type Result f a
  type instance Result f a = a
  applyFunc :: (Constraints f a) => f -> a -> Result f a

pairmap :: (Function f, Constraints f a, Constraints f b) => f -> (a, b) -> (Result f a, Result f b)
pairmap f (x,y) = (applyFunc f x, applyFunc f y)

data NumFunc where
  NumFunc :: (forall a. Num a => a -> a) -> NumFunc

instance Function NumFunc where
  type Constraints NumFunc a = (Num a)
  applyFunc (NumFunc f) = f

data EnumFunc where
  EnumFunc :: (forall a. Enum a => a -> a) -> EnumFunc

instance Function EnumFunc where
  type Constraints EnumFunc a = (Enum a)
  applyFunc (EnumFunc f) = f

data MaybeFunc where
  MaybeFunc :: (forall a. a -> Maybe a) -> MaybeFunc

instance Function MaybeFunc where
  type Result MaybeFunc a = Maybe a
  applyFunc (MaybeFunc f) = f

y1 = pairmap (NumFunc (+2)) (1::Int, 2::Float)
y2 = pairmap (EnumFunc succ) (1::Int, 'a')
y3 = pairmap (MaybeFunc Just) ('a', True)

main = do
  print y1
  print y2
  print y3