Traversable list

Traversable list.scala

trait ListLike[C[_]] {
  def cons[T](x: T, xs: C[T]): C[T]

  def empty[T](): C[T]

  def first[T](source: C[T]): Option[T]

  def rest [T](source: C[T]): C[T]

}

trait TraverseListLike[C[_]] extends Traverse[C]{
  self : ListLike[C] =>

  override def traverse[M[_], T, U](source: C[T])(f: (T) ⇒ M[U])(implicit applicative: Applicative[M]): M[C[U]] = {
    first(source) match {
      case Some(value) ⇒
        cons[U] _ :@:f(value):*:traverse(rest(source))(f)
      case _ ⇒ applicative(empty[U]())
    }
  }
}

  implicit object traversableList extends TraverseListLike[List] with ListLike[List]{

    def empty[T]() = Nil

    def cons[T](x: T, xs: List[T]) = x::xs

    def first[T](source: List[T]) = source.headOption

    def rest[T](source: List[T]) = source.tail
  }