sclass Corridor {
  record noeq Position(settable double openingPrice, settable double direction) {
    settable double closingPrice = Double.NaN;
    
    void close {
      openPositions.remove(this);
      closingPrice = currentPrice();
      closedPositions.add(this);
    }
  }
      
  settable double ladderStep = 1;
  gettable double currentPrice = 0;
  new L<Loop> loops;
  new LinkedHashSet<Position> openPositions;
  new L<Position> closedPositions;
  
  record noeq Loop(settable double startingPrice, settable double direction) {
    Position position;
    Loop successor;
    
    selfType init {
      loops.add(this);
      addThreshold(startingPrice+ladderStep, direction, -> {
        position = openPosition(direction);
        if (successor == null)
          successor = new Loop(x+ladderStep, direction).init();
      });
      
      addThreshold(startingPrice-ladderStep, -direction, -> {
        position.close();
      });
    }
  }
  
  Position openPosition(double direction) {
    ret addAndReturn(openPositions, new Position(currentPrice(), direction));
  }
  
  void start {
    double price = currentPrice();
    new Loop(price-ladderStep, 1).init();
    new Loop(price+ladderStep, -1).init();
  }
}