fn fib(n: u32) -> u32 {
    var index: u32 = 0
    var a: u32 = 0
    var b: u32 = 1
    while index < n {
        let next: u32 = a + b
        a = b
        b = next
        index = index + 1
    }
    return a
}

pub fn main(world: World) -> Void raises {
    if fib(10) == 55 {
        check world.out.write("fib iterative ok\n")
    }
}