Read integer from prompt

[Li Peng]

hi
    In the older hugs, i do this to read in integer from standard input:

        readNum :: IO Integer
        readNum  = do {
                          line <- getLine
                        ; readIO line
                      }

     However, in hugs98, it failed and the error message is:
        User error: PreludeIO.readIO: no parse

     Why? And can anybody tell me how to read in integer in hugs98

lipeng