override def foldRight[B](z: B)(op: (A, B) => B): B =
    reverse.foldLeft(z)((right, left) => op(left, right))

  def fold[A1 >: A](z: A1)(op: (A1, A1) => A1): A1 = foldLeft(z)(op)

  def reduceLeft[B >: A](op: (B, A) => B): B = {
    val it = iterator
    if (it.isEmpty)
      throw new UnsupportedOperationException("empty.reduceLeft")

    var first = true
    var acc: B = null.asInstanceOf[B]

    while (it.hasNext) {
      val x = it.next()
      if (first) {
        acc = x
        first = false
      }
      else acc = op(acc, x)
    }
    acc
  }

  def foldLeft[B](z: B)(op: (B, A) => B): B = {
    var result = z
    val it = iterator
    while (it.hasNext) {
      result = op(result, it.next())
    }
    result
  }

  def reduceLeft[B >: A](op: (B, A) => B): B = {
    val it = iterator
    if (it.isEmpty)
      throw new UnsupportedOperationException("empty.reduceLeft")

    var first = true
    var acc: B = null.asInstanceOf[B]

    while (it.hasNext) {
      val x = it.next()
      if (first) {
        acc = x
        first = false
      }
      else acc = op(acc, x)
    }
    acc
  }

  def foldLeft[B](z: B)(op: (B, A) => B): B = {
    var result = z
    val it = iterator
    while (it.hasNext) {
      result = op(result, it.next())
    }
    result
  }