static <A> L<A> lazyListFromIterator(Iterator<A> it) {
  ret new RandomAccessAbstractList<A>() {
    new L<A> list;
    
    public int size() { realizeFully(); ret list.size(); }
    public A get(int i) { realizeUpTo(i); ret list.get(i); }
    
    void realizeUpTo(int i) {
      while (i >= list.size() && it.hasNext())
        list.add(it.next());
    }
    
    void realizeFully() {
      realizeUpTo(Int.MAX_VALUE);
    }
  };
}