T8851.hs:24:12: error:
    Couldn't match type ‘Parser’ with ‘MyParser’
      arising from the coercion of the method ‘notFollowedBy’
        from type ‘forall a.
                   (Monad Parser, Show a) =>
                   Parser a -> Parser ()’
          to type ‘forall a.
                   (Monad MyParser, Show a) =>
                   MyParser a -> MyParser ()’
    When deriving the instance for (Parsing MyParser)