modalduality

    case (xm, ym) of
        (Just x, Just y) -> x + y
        _ -> 0

    URL: ^(((http|https|ftp):\/\/)?([[a-zA-Z0-9]\-\.])+(\.)([[a-zA-Z0-9]]){2,4}([[a-zA-Z0-9]\/+=%&_\.~?\-]*))*$

    fn main() {
        let (a, b) = (5, 2);
        println!("{}, {}", b, a);
    }