if (currIdx < size) return items[++currIdx]; else throw new NoSuchElementException();
if (currIdx < size) { Sexp nextItem = items[currIdx]; currIdx++; return nextItem; } else throw new NoSuchElementException();
  public Iterator iterator() {    return new Iterator() {      int currIdx = 0;      public boolean hasNext() { return currIdx < size; }      public Object next() {        if (currIdx < size)          return items[++currIdx];        else          throw new NoSuchElementException();      }      public void remove() {        throw new UnsupportedOperationException();      }    };  }