switch ( x ){
case 0:
    do_something();
case 1:
    do_something();
case 2:
    do_something();
}


switch ( x, y ){
case Zero, Zero:
    return Zero;
case Zero, Succ(n):
    return n;
case Succ(n), Zero:
    return n;
case Succ(n), Succ(m):
    return Succ(Succ(add(n, m)));
}