sclass WithTimestamp<A> extends Var<A> {
  long timestamp;
  
  *() {}
  *(long *timestamp, A value) { super(value); }
  
  toString { ret toStringWithTimestamp(super.toString()); }
  S toStringQuoted() { ret toStringWithTimestamp(quote(super.toString())); }
  
  S toStringWithTimestamp(S s) { ret s + " at " + localTimeWithMilliseconds(timestamp); }
}