splitBy.scala

implicit class RichTraversable[A, C[B] <: TraversableLike[B, C[B]]](val wrapped: C[A]) extends AnyVal {
  def splitBy(p: A => Boolean)(implicit cb: CanBuild[Either[C[A], C[A]], C[Either[C[A], C[A]]]]): C[Either[C[A], C[A]]] = {
    val builder = cb()

    @tailrec def spanNext(as: C[A]): Unit =
      if (as.nonEmpty) {
        val ph = p(as.head)
        val (append, remaining) = as.span(a => p(a) == ph)
        builder += (if (ph) Right(append) else Left(append) : Either[C[A], C[A]])
        spanNext(remaining)
      }

    spanNext(wrapped)
    builder.result()
  }
}