fn fib(n: u32) -> u32 {
    if n < 2 {
        return n
    }
    return fib(n - 1) + fib(n - 2)
}

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