stem_pull.lua

local stem = require("stem")
local event = require("event")
local modem = require("component").modem
local messages = {}
local server = stem.connect('stem.fomalhaut.me')
server:subscribe('stem-test')

modem.open(666)


while true do
  local ev = {event.pull()}
  if ev[1] == "stem_message" then
    messages[ev[3]] = ev[3]
  elseif ev[1] == "modem_message" then
    if messages[ev[6]] then
      print("OK!")
    else
      print("ERROR: "..ev[6])
    end
  end
end