Python-style classes in lua

pyclass.lua

--quick implementation of python's id function. Fails for built in roblox objects
id = function(o)
	return type(o) == "table" and o.__id__ or tonumber(tostring(o):sub(-8, -1). 16)
end

class = setmetatable({}, {
	__call = function(_, name, implementer)
		local cls = {__init__ = function() end, __name__ = name}
		local instancemt = {}

		--implement method lookups and descriptors (such as properties)
		function instancemt:__index(k)
			local member = cls[k]
			if type(member) == "table" and member.__get__ then
				return member:__get__(self)
			else
				return member
			end
		end
		function instancemt:__newindex(k, v)
			local member = cls[k]
			if member then
				if type(member) == "table" and member.__set__ then
					member:__set__(self, v)
				else
					error("Cannot set static member from non-static context")
				end
			else
				rawset(self, k, v)
			end
		end

		--tostring method
		function instancemt:__tostring(k, v)
			local str = cls.__str__ or cls.__repr__
			if str then
				return str(self)
			else
				return ("<%s instance at 0x%X>"):format(name, self.__id__)
			end
		end

		--Add binary operators
		for _, binop in ipairs({'add', 'sub', 'mul', 'div', 'mod', 'pow'}) do
			local luaname = ("__%s"):format(binop)
			local newname = ("__%s__"):format(binop)
			local rname = ("__r%s__"):format(binop)

			instancemt[luaname] = function(a, b)
				if getmetatable(a) == instancemt then
					if cls[newname] then
						return cls[newname](a, b)
					else
						error()
					end
				elseif getmetatable(b) == instancemt then
					if cls[rname] then
						return cls[rname](b, a)
					else
						error()
					end
				end
			end
		end



		--define the constructor
		setmetatable(cls, {
			__call = function(self, ...)
				local instance = {__class__ = cls}
				instance.__id__ = id(instance)
				setmetatable(instance, instancemt)
				instance:__init__(...)
				return instance
			end
		})

		--call oldenv in an environment that proxies to the class object 
		local oldenv = getfenv(implementer)
		setfenv(implementer, setmetatable({}, {
			__index = function(_, k)
				if cls[k] ~= nil then
					return cls[k]
				else
					return oldenv[k]
				end
			end,
			__newindex = cls
		}))(cls)

		return cls
	end,
	--syntactic sugar
	__index = function(self, name)
		return function(_, f)
			getfenv()[name] = self(name, f)
		end
	end
});

class: property(function()
	function __get__(self, instance)
		if self.getter then return self.getter(instance) else error() end
	end
	function __set__(self, instance, value)
		if self.setter then self.setter(instance, value) else error() end
	end
end)