sclass SimpleFactStore implements IFactStore {
  L<Fact> facts = synchroList();
  transient bool verbose;
  transient L<Runnable> onChange = syncList();
  
  sclass Fact extends HasGlobalID {
    long created = now();
    S text;
    
    *() {}
    *(S *text) {}
    
    toString { ret text; }
  }
  
  public void store(S fact) {
    if (!any(facts, f -> eqic(f.text, fact))) {
      facts.add(new Fact(fact));
      pcallFAll(onChange);
    }
  }
  
  public void deleteAll(IPred<S> filter) {
    for (Fact f : cloneList(facts))
      if (filter.get(f.text)) {
        if (verbose)
          print("Deleting fact: " + f);
        facts.remove(f);
        pcallFAll(onChange);
      }
  }
  
  public LS facts() { ret map(facts, f -> f.text); }
  
  toString {
    ret sfu(this);
  }
  
  void onChange(Runnable r) { onChange.add(r); }
  
  void clear { facts.clear(); pcallFAll(onChange); }
}