sclass Chain<A> implements Iterable<A> {
  A element;
  Chain<A> next;
  int size;
  
  *() {}
  *(A *element) { size = 1; }
  *(A *element, Chain<A> *next) {
    size = next != null ? next.size+1 : 1;
  }
  
  toString { ret str(toList()); }
  
  ArrayList<A> toList() {
    ArrayList<A> l = emptyList(size);
    Chain<A> c = this;
    while (c != null) {
      l.add(c.element);
      c = c.next;
    }
    ret l;
  }
  
  // TODO: optimize
  public Iterator<A> iterator() { ret toList().iterator(); }
}