fn quicksort<'a, T: Ord, Iter: Iterator<T>>(i: Iter) -> Box<Iterator<T>+'a> {
    box {
        let p = i.next().unwrap();
        let l = i.by_ref().filter(|x| *x <= p);
        let r = i.by_ref().filter(|y| *y > p);

        quicksort(l).chain(vec![p].iter()).chain(quicksort(r))
    }
}

fn main() {
    quicksort(vec![1,2,3].iter())
}