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  1. {-# OPTIONS -fglasgow-exts #-}
  2.  
  3.  
  4. f :: Maybe (forall a. [a] -> [a]) -> Maybe ([Int], [Char])
  5. f (Just g) = Just (g [3], g "hello")
  6. f Nothing = Nothing
  7.  
  8. main = print $ f (Just reverse)
Success #stdin #stdout 0.02s 3544KB
stdin
Standard input is empty
stdout
Just ([3],"olleh")