sclass LearnNumberRange {
  double min = positiveInfinity(), max = negativeInfinity();
  
  void learn(Number n) {
    if (n != null) {
      double d = toDouble(n);
      min = min(d, n);
      max = max(d, n);
    }
  }
  
  bool empty() { ret min == positiveInfinity(); }
}