fold.scala

def kaiFold[A, B](stuff: Seq[A], initial: B)(predicate: (B, A) => B): B = {
  @tailrec
  def it(items: Seq[A], accumulator: B): B = {
    if (items.length == 0) accumulator
    else {
      val nextAccumulator = predicate(accumulator, items.head)
      it(items.tail, nextAccumulator)
    }
  }

  it(stuff, initial)
}

val stuff = Vector(1, 2, 3)
kaiFold(stuff, 0)((p: Int, e: Int) => p + e)