fn collatz_steps(n: int) -> int {
    if n == 1 {
        0
    } else {
        1 + collatz_steps(if n % 2 == 0 { n / 2 } else { 3*n + 1 })
    }
}

fn find_collatz(k: int) -> int {
    // Returns the minimum value, n, with Collatz stopping time >= k.
    let mut n = 1;
    let max_tasks = 7; // keep all my cores busy

    let mut found_result = false;
    let mut result = -1; // need to initialize

    while !found_result {
        let mut ports = ~[];

        for i in range(0, max_tasks) {
            let val = n + i;
            let (port, chan) : (Port<int>, Chan<int>) = Chan::new();
            ports.push(port);

            spawn(proc() { 
               let steps = collatz_steps(val);
               println!("Result for {}: {}", val, steps);
               chan.send(steps);
	    });
        }

        for i in range(0, max_tasks) {
            let port = ports.pop();
            let steps = port.recv();
            if steps > k {
                found_result = true;
                result = n + i;
            }
        }
        n += max_tasks;
    }

    assert!(result != -1);
    result
}
    
fn main() {
    println!("Result: {}", find_collatz(500));
}