sclass ReverseChain<A> implements Iterable<A> {
  A element;
  ReverseChain<A> prev;
  int size;
  
  *() {}
  *(ReverseChain<A> *prev, A *element) {
    if (prev == null) size = 1;
    else {
      prev.check();
      size = prev.size+1;
    }
  }
  
  void check {
    if (size < 1) fail("You called the ReverseChain default constructor. Don't do that");
  }
  
  toString {
    ret str(toList());
  }
  
  ArrayList<A> toList() {
    check();
    ArrayList<A> l = emptyList(size);
    for i to size: l.add(null);
    int i = size;
    ReverseChain<A> c = this;
    while (c != null) {
      l.set(--i, c.element);
      c = c.prev;
    }
    ret l;
  }
  
  public Iterator<A> iterator() { ret toList().iterator(); }
}