require 'generator'

module Enumerable
  class Product
    include Enumerable

    def initialize(first, second)
      @first  = first
      @second = second
    end

    def each
      xg = Generator.new(@first)
      yg = Generator.new(@second)
      xa = Array.new
      ya = Array.new

      n = 0
      loop{
        xa << xg.next unless xg.end?
        ya << yg.next unless yg.end?
        break if xa.size + ya.size - 2 < n
        n.downto(0){|x|
          y = n - x
          yield(xa[x], ya[y]) if x < xa.size and y < ya.size
        }
        n = n.succ
      }
    end

    def member?(obj)
      obj.is_a?(Array) and @first.member?(obj[0]) and @second.member?(obj[1])
    end
    alias include? member?
    alias === member?
  end
end