gistfile1.rs

pub fn freplace<T>(mut src: T, dest: &mut T) -> T {
    util::swap(dest, &mut src);
    src
}

fn pop<T>(prev: &mut ~List<T>) -> Option<~List<T>> {
    Some(freplace(util::replace(match prev {
        &~Cons(_, ref mut rs) => rs,
        &~Nil => return None
    }, ~Nil), prev))
}