Cartesian product of two or more lists

# title: Cartesian product of two or more lists
# source: https://rosettacode.org/wiki/Cartesian_product_of_two_or_more_lists
# category: Rosetta Code
# difficulty: Intro
# summary: Build Cartesian products iteratively for a pair of lists and a three-list input.
# tags: popular, arrays, combinatorics, iteration
# vibe: 0.2

def cartesian_product(lists)
  combinations = [[]]
  list_index = 0

  while list_index < lists.length
    current = lists[list_index]
    next_combinations = []
    combination_index = 0

    while combination_index < combinations.length
      prefix = combinations[combination_index]
      value_index = 0
      while value_index < current.length
        next_combinations = next_combinations.push(prefix + [current[value_index]])
        value_index = value_index + 1
      end
      combination_index = combination_index + 1
    end

    combinations = next_combinations
    list_index = list_index + 1
  end

  combinations
end

def run
  {
    two_lists: cartesian_product([["red", "blue"], [1, 2, 3]]),
    three_lists: cartesian_product([["small", "large"], ["circle", "square"], ["solid", "outline"]])
  }
end