macros.alu

fn printf_impl(fmt: &[u8], args: &[&void]) {
    let i = 0usize;
    let buf: [u8; 32];
    let buf: &mut [u8] = &buf;

    let buf_pos = 0usize;
    let in_escape = false;

    // Macros are hygienic, but if defined in linear scopes,
    // they can bind ambient variables (like buf, buf_pos here)
    macro buf_append($val) {
        buf[buf_pos] = $val;
        buf_pos += 1;
        if buf_pos == buf.len() {
            print!("{}", buf);
            buf_pos = 0;
        }
    }

    macro pop_arg() {
        if args.len() == 0 {
            panic!("too few arguments");
        }
        let arg = args[0];
        args = args[1..];
        arg
    }

    while i < fmt.len() {
        let ch = fmt[i];
        if in_escape {
            switch ch {
                's' => {
                    print!("{}", buf[0..buf_pos]);
                    print!("{}", *(pop_arg!() as &&[u8]));
                    buf_pos = 0;
                }
                'd' => {
                    print!("{}", buf[0..buf_pos]);
                    print!("{}", *(pop_arg!() as &i32));
                    buf_pos = 0;
                }
                '%' => {
                    buf_append!(ch);
                }
                _ => {
                    panic!("unknown escape code")
                }
            }
            in_escape = false;
        } else {
            if ch == '%' {
                in_escape = true;
            } else {
                buf_append!(ch);
            }
        }
        i += 1;
    }

    print!("{}", buf[0..buf_pos]);

    if args.len() > 0 {
        panic!("too many arguments");
    }
}

macro printf($fmt, $expr...) {
    printf_impl($fmt, &[(&$expr as &void)$...])
}


fn main() {
    printf!(
        "hello %s, you are %d years old, you have %d dogs and %d cats\n",
        "user",
        42,
        3,
        6
    );

    // Macros can also be invoked using universal call syntax
    "%d + %d = %d\n".printf!(1, 2, 3);
}