calculating multiplicative persistence in Lua

mult-persistence.lua

local function per (n, steps)
	steps = steps or 0
	if n < 10 then return steps end
	local m = 1
	for d in string.gmatch (tostring (n), ".") do
		m = m * tonumber (d)
	end
	print ("STEP #" .. steps+1 .. ": " .. n .. " -> " .. m)
	return per (m, steps+1)
end

repeat
	io.write ("> ")
	local n = io.read("*n") 
	print ("#steps = " .. per (n))
until not n