flodleft and fold right

def foldLeft[B](z: B)(op: (B, A) => B): B = {
    var result = z
    this.seq foreach (x => result = op(result, x))
    result
  }


def foldRight[B](z: B)(op: (A, B) => B): B =
    reversed.foldLeft(z)((x, y) => op(y, x))

参见：
http://blog.csdn.net/oopsoom/article/details/23447317