Cloning a function in Lua - http://leafo.net/guides/function-cloning-in-lua.html

function-clone.lua

local function clone_function(fn)
  local dumped = string.dump(fn)
  local cloned = loadstring(dumped)
  local i = 1
  while true do
    local name = debug.getupvalue(fn, i)
    if not name then
      break
    end
    debug.upvaluejoin(cloned, i, fn, i)
    i = i + 1
  end
  return cloned
end

-- example
-- an upvalue to keep reference of
local message = "Hello"

-- the function to clone
local function say_message()
  print("message: " .. tostring(message))
end

local say_message_clone = clone_function(say_message)
-- the clone now has a functional upvalue
say_message_clone() -- message: Hello
message = "MoonScript"
say_message_clone() -- message: MoonScript