class Queue[+T] {

    var queue : (List[T],List[T])

    def empty = {
      queue = (Nil,Nil)
    }

    def enqueue(element : T,queue : Queue[T]) = {
      queue.queue match{
        case (Nil,Nil) => (element,Nil)
        case (l1,l2) => (l1,element::l2)
      }
    }

    def dequeue = {
      queue match{
        case (_,Nil) => this
        case (_,l2) => (l2.reverse,Nil)
        case (_::t,l2) => (t,l2)
        case (Nil,Nil) => (Nil,Nil)
      }
    }
    def first = {
      queue match{
        case (Nil,Nil) => throw new Exception("Queue is empty")
        case (h::_,_) => h
      }
    }
    def isEmpty = {
      queue.equals((Nil,Nil))
    }
}

var pointQueue = new Queue[Point]
var pixelQueue = new Queue[Pixel]

pointQueue = pixelQueue



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

import java.awt.Color

class Pixel(xp:Double=0.0,yp:Double=0.0,var color:Color = Color.BLACK) extends Point(xp, yp) {
override def toString = super.toString + " " + color
}