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+{-# LANGUAGE FunctionalDependencies #-}
+
+-- Exercise 10.1-i
+-- Defunctionalize `listToMaybe :: [a] -> Maybe a`.
+newtype ListToMaybe a = ListToMaybe [a]
+
+class Eval l t | l -> t where
+  eval :: l -> t
+
+instance Eval (ListToMaybe a) (Maybe a) where
+  eval (ListToMaybe []) = Nothing
+  eval (ListToMaybe (x : _)) = Just x