--I should note that client is a number.
module(..., package.seeall)
local LoggedIn = { }

function isLogged( client )
    return LoggedIn[client]
end

function logIn(client)
    table.insert(LoggedIn,client,true)
end

function logOut(client)
    table.remove(LoggedIn,client)
end

package.loaded.myModule= nil; require "myModule"

function event( client )
    myModule.logIn(client)
end

function event_2( client )
    myModule.logOut(client)
end

-- myModule.lua
module(..., package.seeall)

LoggedIn = {}

function isLoggedIn(client)
    return LoggedIn[client] ~= nil
end

function LogIn(client)
    LoggedIn[client] = true
end

function LogOut(client)
    LoggedIn[client] = nil
end

-- main.lua
require "myModule"

myModule.LogIn("Joe")
myModule.LogIn("Frank")

print(myModule.isLoggedIn("Bill"))
print(myModule.isLoggedIn("Frank"))

myModule.LogOut("Joe")
print(myModule.isLoggedIn("Joe"))

false
true
false

package.loaded.myModule= nil; require "myModule"
function event( client )
    myModule.LoggedIn[client] = true
end

event("foo")
print(myModule.isLogged("foo"))

local myModule = require "myModule"
function event( client )
    myModule.logIn(client)
end

event("foo")
print(myModule.isLogged("foo"))
print(myModule.isLogged("bar"))

local LoggedIn = { }
function isLogged( client )
  return LoggedIn[client]
end
function logIn( client )
  LoggedIn[client] = true
end
return { LoggedIn = LoggedIn, isLogged = isLogged, logIn = logIn }