io::read_command!

macro_rules! read_command {
    () => ({
        match {
            read_character!()
        } {
            Some(47) => read_command!(0u64),
            _ => None ,
        }
    });
    ($start: expr) => ({
        extern crate io;
        read_command!($start, io::ffi::BUFF_READ_COMMAND)
    });
    ($start: expr, $limit: expr) => ({
        fn result (
            acc: u64,
            lim: usize
        ) -> Option<u64> {
            match {
                (read_character!(), lim)
            } {
                (Some(d @  97...122), lim) if lim != 0 => {
                    result(10 + acc * 100 + {d - 97i8} as u64, lim -1)
                },
                _ => Some(acc),
            }
        }
        result($start as u64, $limit)
    });
}

The read_command macro reads and returns the concat of all letter.