strict.lua

--
-- strict.lua
-- checks uses of undeclared global variables
-- All global variables must be 'declared' through a regular assignment
-- (even assigning nil will do) in a main chunk before being used
-- anywhere or assigned to inside a function. When __EXTRASTRICT is set
-- then even declarations in a main chunk will result in an error.
--

local mt = getmetatable(_G)
if mt == nil then
   mt = {}
   setmetatable(_G, mt)
end

__EXTRASTRICT = __EXTRASTRICT or false
__STRICT = true
mt.__declared = {}

mt.__newindex = function (t, n, v)
   if __STRICT and not mt.__declared[n] then
	  local w = debug.getinfo(2, "S").what
	  if w ~= "main" and w ~= "C" then
		 error("assign to undeclared variable '"..n.."'", 2)
	  elseif __EXTRASTRICT then
		 error("assign to undeclared variable '"..n.."'", 2)
	  end
	  mt.__declared[n] = true
   end
   rawset(t, n, v)
end

mt.__index = function (t, n)
   if not mt.__declared[n] and debug.getinfo(2, "S").what ~= "C" then
	  error("variable '"..n.."' is not declared", 2)
   end
   return rawget(t, n)
end