persistable abstract sclass AbstractJuicer extends MetaWithChangeListeners {
  // what we are monitoring & closing (a position or a strategy)
  settableWithVar Juiceable juiceable;
  
  settableWithVar double seenJuiceValue;
  
  // must return a new list
  swappable L<SignalWithStrength> calculateCloseSignals() { ret new L; }
  
  double juiceValue() {
    seenJuiceValue(juicable.juiceValue());
    ret seenJuiceValue;
  }
}