A controlled permutation. Cycles an array of arrays calling the proc with each possible set of the sub arrays whilst preserving the positions of the original array. Basically gets every combination of "One from column A, one from column B, ..." and so on.

controlled_perm.rb

a_of_a = [["Jazz", "Soul", "Rock"],["Cheeseburgers", "Hot dogs", "Milkshakes"], ["cable", "radio", "internet"]]
result = Array.new(a_of_a.length)
procky = Proc.new { |arg|
  print arg.join(" and "), " are my favorite things. \n"
}
def controlled_perm(x, a_of_a, result, procky)
	x += 1
	if a_of_a.length == x
			procky.call(result)
		return
	end
	a_of_a[x].each { |pointer|
		result[x] = pointer
		controlled_perm(x, a_of_a, result, procky)
	}
end

controlled_perm(-1, a_of_a, result, procky)