local function permutation(a, n, cb)
	if n == 0 then
		cb(a)
	else
		for i = 1, n do
			a[i], a[n] = a[n], a[i]
			permutation(a, n - 1, cb)
			a[i], a[n] = a[n], a[i]
		end
	end
end

--Usage
local function callback(a)
	print('{'..table.concat(a, ', ')..'}')
end
permutation({1,2,3}, 3, callback)