Mucking with NonEmptyList discussing with friend

NonEmptyCopyAndMuck

sealed trait NonEmptyList[+A] {
  val head: A
  val tail: List[A]

  import Scalaz._

  def <::[B >: A](b: B): NonEmptyList[B] = nel(b, head :: tail)

  import collection.mutable.ListBuffer

  def <:::[B >: A](bs: List[B]): NonEmptyList[B] = {  //Scary
    val b = new ListBuffer[B]
    b ++= bs
    b += head
    b ++= tail
    val bb = b.toList
    nel(bb.head, bb.tail)
  }