class Array

  def zip(a, &b)
    if b
      r = []
      bs = lambda{ |x| r << b.call(*x) }
      super(a, &bs)
      return r
    else
      super(a)
    end
  end

end

# example
[1,2,3].zip([5,6,7], &:+)  #=> [6,8,10]