breadth_first_product.ex

defmodule Test do

    defp add(product, {i, list_i}, {j, list_j}, max) do
      p = [{elem(list_i, i), elem(list_j, j)} | product]
      reverse(p, {j, list_i}, {i+1, list_j}, max)
    end

    defp reverse(product, {i, list_i}, {j, list_j}, max) do
      p = [{elem(list_i, i), elem(list_j, j)} | product]

      case j do # next step?
        ^max ->         p                                   # done
        ^i   -> reverse(p, {i+1, list_i}, {0, list_j}, max) # new
         j   ->     add(p, {j  , list_i}, {i, list_j}, max) # normal
      end
    end


  def breadth_first_product(list1, list2) do
    e = reverse([], {0, List.to_tuple(list1)}, {0, List.to_tuple(list2)}, length(list1)-1) |> Enum.reverse
  end

end