// returns last value
sclass PrintPolledValueUntilPredicateOrTimeout {
  settable IF0<A> makeValue;
  settable IPred<A> shouldEnd;
  settable double timeout = 60.0;
  settable int interval = 100;
  settable S printPrefix = "";
  
  void printValue(A a) {
    print(printPrefix, a);
  }
  
  run {
    Timeout timeOut = new(timeout);
    A a = makeValue!;
    printValue(a);
    if (pred != null && pred.get(a))
      break;
    while (!timeOut!) {
      A b = makeValue!;
      if (!eq(a, b))
        printValue(a = b);
      if (pred != null && pred.get(a))
        break;
      else
        sleep(interval);
    }
    ret a;
  }
}