RepPolyCase2.hs:33:7: error: [GHC-55287]
    • The scrutinee of the case statement
      does not have a fixed runtime representation.
      Its type is:
        Unbox Int :: TYPE (Rep Int)
    • In the expression: case unbox (3 :: Int) of _ -> ()
      In an equation for ‘x’: x _ = case unbox (3 :: Int) of _ -> ()