class Point(var x:Double = 0.0,
             var y:Double = 0.0) {
  override def toString = "[" + x + ", " + y + "]"
}


class Pixel(xp:Double =0.0,
             yp:Double =0.0) extends Point(xp, yp) {
  override def toString = super.toString + " "
}
class EmptyException(msg: String) extends Exception(msg)
trait MyList[T] {
  def enqueue(el: T): MyList[T]
  def first: T
  def dequeue: MyList[T]
  def isEmpty: Boolean
}
object  MyList {
  def apply[T](xs: T*): MyList[T] = new Queue[T](xs.toList, Nil)
  def empty[T]: MyList[T] = new Queue[T](Nil, Nil)

  private class Queue[T](private val x: List[T], private val y: List[T]) extends MyList[T] {
    def enqueue(el: T) =
      normalize(x, el::y)
    def first =
      x match {
      case x::_ => x
      case Nil  => throw new EmptyException("Empty queue")
    }
    def dequeue =
      x match {
      case _::xs  => normalize(xs, y)
      case Nil     => this
    }
    def isEmpty =
      x == Nil
    def normalize(xx:List[T], yy:List[T]) =
      if (xx == Nil) new Queue(yy.reverse, Nil)
      else new Queue(xx, yy)
  }
}
val po=new Point(3,4)
po.toString
val px=new Pixel(5,6)
px.toString
var queue1 = MyList(po)
val queue2 = queue1.enqueue(px)
println(queue2.first)