Lua set permutations of N iterator with coroutines

permutations.lua

local table = require 'table'

function permutations(N)
	local level, set, co = -1, {}, nil

	for i = 1, N do set[i] = 0 end

	co = coroutine.create(function () permute(set, level, N, 1) end)

	return function ()
		local _, p = coroutine.resume(co)
		return p
	end
end 

function permute(set, level, N, k)
	level = level + 1
	set[k] = level
	if level == N then
		coroutine.yield(set)
	else
		for i = 1, N do
			if set[i] == 0 then
				permute(set, level, N, i)
			end
		end
	end

	level = level - 1
	set[k] = 0
end

return permutations

usage.lua

local table = require 'table'
local permutations = require 'permutations'

for p in permutations(n) do
	print(table.concat(p, ' '))
end