../Plugin.hs:5:31:
    Couldn't match the rigid variable `a' against `Int'
      `a' is bound by the polymorphic type `forall a. (Num a) => a -> a -> a'
			at ../Plugin.hs:5:11-56
      Expected type: a -> a -> a
      Inferred type: Int -> Int -> Int
    In the expression: (+) :: Int -> Int -> Int
    In the `function' field of a record