experiment.lua

local Experiment = {}
Experiment.__index = Experiment

function Experiment:create(urls)
   local experiment = {}
   setmetatable(experiment, Experiment)
   experiment.urls = urls
   return experiment
end

function Experiment:run()
   error("Undefined function run")
end

return Experiment

http.lua

local http = require("socket.http")
local Experiment = require "experiment"

local HttpRequestExperiment = {}
HttpRequestExperiment.__index = HttpRequestExperiment

setmetatable(HttpRequestExperiment, {
                __index = Experiment
             })

function HttpRequestExperiment:run()
   for _, url in pairs(self.urls) do
      body, status_code, header, status_line = http.request(url)
      if status_code == 200 then
         print("Url:", url)
         print("Status: ", status_code)
      end
   end
end

urls = {"http://www.google.com"}
exp = HttpRequestExperiment:create(urls)
exp:run()

-- sathya@sathya:~/tests|master:  lua http.lua
-- lua: ./experiment.lua:12: Undefined function run
-- stack traceback:
--  	[C]: in function 'error'
--	./experiment.lua:12: in function 'run'
--	http.lua:23: in main chunk
--	[C]: ?