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+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE TypeFamilies #-}
+
+-- Exercise 10.4-i
+-- Write a promoted functor instance for tuples.
+
+import Data.Kind (Type)
+
+type Exp a = a -> Type
+
+type family Eval (e :: Exp a) :: a
+
+data Map :: (a -> Exp b) -> f a -> Exp (f b)
+
+type instance Eval (Map f '(a, b)) = '(a, Eval (f b))