Demonstrate how to implement append

simple_list.scala

sealed abstract class L[A] {
  def append(l: L[A]): L[A]
}

case class LNil[A]() extends L[A] {
  def append(l: L[A]) = l
  override def toString = "Nil"
}

case class LCons[A](head: A, tail: L[A]) extends L[A] {
  def append(l: L[A]): L[A] = LCons(head, tail.append(l))
  override def toString = head.toString + " :: " + tail.toString
}

val l1 = LCons(1, LNil[Int])
val l2 = LCons(2, LCons(3, LNil[Int]))
val l3 = LCons(4, LCons(5, LCons(6, LNil[Int])))

println(l1)                       // 1 :: Nil
println(l2)                       // 2 :: 3 :: Nil
println(l3)                       // 4 :: 5 :: 6 :: Nil
println(l3.append(l2).append(l3)) // 4 :: 5 :: 6 :: 2 :: 3 :: 4 :: 5 :: 6 :: Nil