abstract sclass DynCalculatedList extends DynModule {
  transient JList list;
  transient L<S> results;
  transient bool calculateWhenHidden;

  visualize { ret list = jlist(calc()); }
  void unvisualize() { list = null; }  
  void update() {
    temp enter();
    if (list != null || calculateWhenHidden)
      fillListWithStrings(list, results = calc());
  }

  // Note: This is called on every update, so you should cache
  // results IN the calc function if they are expensive to make
  abstract L<S> calc();
  
  void scrollDown {
    scrollAllTheWayDown(list);
  }
  
  S selected() { ret selectedItem(list); }
}

Began life as a copy of #1015929