{-# LANGUAGE DataKinds #-}
{-# LANGUAGE TypeFamilies #-}
module M where

import GHC.TypeLits

data A = A1 | A2
data B = B1 | B2

type family K (n :: Nat) where
  K 0 = A
  K 1 = A
  K 2 = B
  K 3 = B

type F :: forall (n :: Nat) -> K n
type family F n where
     F 0 = 'A1
     F 1 = 'A2
     F 2 = 'B1
     F 3 = 'B2