persistable sclass BoolVar {
  bool a; // you can access this directly if you use one thread
  
  *() {}
  *(bool *a) {}
  
  public synchronized void set(bool v default true) {
    if (v != a) {
      a = v;
      notifyAll();
    }
  }
  
  public synchronized bool get() { ret a; }
  //public synchronized bool has() { true; }
  public void clear aka unset() { set(false); }
  
  bool waitUntilTrue () { ret waitForValue(true); }
  bool waitUntilFalse() { ret waitForValue(false); }
  
  synchronized bool waitForValue(bool wantedValue) ctex {
    while (a != wantedValue)
      wait();
    ret a;
  }
  
  public synchronized bool getAndSet(bool b) {
    var value = a;
    set(b);
    ret v;
  }
}