A replacement/wrapper for lua's require

require.lua

local _G = _G
local next , pairs , rawset , require = next , pairs , rawset , require

local cache = { }

---A new require: loads modules in a way that they don't modify the global environment
--@param lib			module name to load (given to require)
--@param keepchanges	whether changes to existing global keys should be kept (default is to revert changes)
local function newrequire ( lib , keepchanges )
	-- Check if its in the cache
	local cachedver = cache [ lib ]
	if cachedver ~= nil then return cachedver end

	-- Save current _G
	local old_G = { }
	for k , v in pairs ( _G ) do
		old_G [ k ] = v
	end

	-- Require the lib
	local res = require ( lib )

	-- Save changes to _G
	local new = { }
	for k , v in pairs ( _G ) do
		if old_G [ k ] == nil then
			new [ k ] = v
			rawset ( _G , k , nil ) -- Delete all new values
		end
	end

	if not keepchanges then -- Restore old _G
		for k , v in pairs ( old_G ) do
			rawset ( _G , k , v )
		end
	end

	local k , v = next ( new )
	if not res and k ~= nil then -- Library doesn't return anything, and is not well behaved (it adds things to global env)
		if k == lib and next ( new , k ) == nil then -- Module only loaded one value, and it was called the same thing as the lib.
			res = v
		else -- Return a table of everything it added to global env.
			res = new
		end
	end

	cache [ lib ] = res
	return res
end

--This file returns the new require function and the cache.
return newrequire , cache