sclass WithProbability<A> extends Var<A> {
  double probability; // assumed between 0 and 1
  
  *() {}
  *(double *probability, A a) { super(a); }
  
  toString {
    ret "p=" + formatDouble_noLeadingZero(probability, 2) + ": " + str(get());
  }
  
  double probability() { ret probability; }
  
  public int hashCode() {
    ret boostHashCombine(main hashCode(probability), main hashCode(get()));
  }
  
  public bool equals(O o) {
    if (o cast WithProbability) {
      ret probability == o.probability && eq(get(), o!);
    }
    false;
  }
}