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+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE UndecidableInstances #-}
+
+-- Exercise 10.2-ii
+-- Defunctionalize `foldr :: (a -> b -> b) -> b -> [a] -> b`.
+
+import Data.Kind (Type)
+
+type Exp a = a -> Type
+
+type family Eval (e :: Exp a) :: a
+
+data Foldr :: (a -> b -> Exp b) -> b -> [a] -> Exp b
+
+type instance Eval (Foldr f z '[]) = z
+
+type instance Eval (Foldr f z (x ': xs)) = Eval (f x (Eval (Foldr f z xs)))