MyList.scala

 sealed trait MyList[+T] {
    def isEmpty: Boolean
    def prepend[R >: T](element: R): MyList[R] = Cons(element, this)
  }

  case class Cons[+T](head: T, tail: MyList[T]) extends MyList[T] {
    override def isEmpty: Boolean = false
  }

  case object EmptyList extends MyList[Nothing] {
    override def isEmpty: Boolean = true
  }