tag blah {
    a(int, int, uint);
    b(int, int);
    c;
}

fn or_alt(&blah q) -> int {
    alt q {
        a(?x, ?y, _) | b(?x, ?y) { ret x + y;}
        c { ret 0; }
    }
}

fn main() {
    assert or_alt(c) == 0;
    assert or_alt(a(10, 100, 0u)) == 110;
    assert or_alt(b(20, 200)) == 220;
}