class CartesianIterator
  def initialize(foo, bar)
    @lists = []
    @tot_iter = 1
    x(foo)
    x(bar)
  end

  def x(other)
    @lists << other.to_a
    @tot_iter *= @lists[-1].size
    self
  end

  def each
    return false if @tot_iter < 1

    elems = []
    for list in @lists
      elems << list.restart_and_raw_next
    end
    yield *elems

    last_list_index = @lists.size-1
    n = last_list_index
    loop do
      if elems[n] = @lists[n].raw_next
        yield *elems
        n = last_list_index
        next
      elsif n > 0
        elems[n] = @lists[n].restart_and_raw_next
        n -= 1
      else
        return true
      end
    end
  end

  def to_a
    array = []
    self.each {|*element| array << element }
    array
  end
end

module Iterable
  def start
    @next_index = -1
    true
  end
  alias :restart :start

  def next
    @next_index or restart
    raw_next
  end

  def raw_next
    self[@next_index += 1]
  end

  def restart_and_raw_next
    self[@next_index = 0]
  end
end

class Array
  include Iterable
end