fn factorial(n: u32) -> u32 {
    var value: u32 = 1
    var index: u32 = 2
    while index <= n {
        value = value * index
        index = index + 1
    }
    return value
}

pub fn main(world: World) -> Void raises {
    if factorial(6) == 720 {
        check world.out.write("factorial ok\n")
    }
}