// This object locates a floating-point key in a sorted map.

// Then it calls (probabilistically schedules) an action function

// on keys from the map, starting with the key closest to the

// requested one, then moving further to the left AND to the right

// until (at possibly very low probability) even the keys farthest

// away have been called.

// Probability 1 is used only iff there is an exact match.

// Probabilities fall with increasing distance between

// searched and found key.

srecord noeq ProbabilisticDistanceBasedLookup(

  IProbabilisticScheduler scheduler,

  NavigableMap<Double, ?> map,

  IVF1<Double> action,

  double key) {

  swappable double distanceToProbability(double distance) {

    ret genericDistanceToProbability(distance);

  }

  run  {

    Double closest = closestDoubleKey(map, key);

    if (closest == null) ret;

    double p = distanceToProbability(abs(closest-key));

    scheduler.at(p, () -> action.get(closest));

    scheduler.at(p, () -> walkLeft(closest));

    scheduler.at(p, () -> walkRight(closest));

  }

  void walkLeft(double x) {

    Double y = map.lowerKey(x);

    if (y == null) ret;

    double p = distanceToProbability(abs(y-key));

    scheduler.at(p, () -> action.get(y));

    scheduler.at(p, () -> walkLeft(y));

  }

  void walkRight(double x) {

    Double y = map.higherKey(x);

    if (y == null) ret;

    double p = distanceToProbability(abs(y-key));

    scheduler.at(p, () -> action.get(y));

    scheduler.at(p, () -> walkRight(y));

  }

}