--- /dev/null
+--
+-- 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.
+--
+-- From Lua distribution (etc/strict.lua)
+--
+
+local getinfo, error, rawset, rawget = debug.getinfo, error, rawset, rawget
+
+local mt = getmetatable(_G)
+if mt == nil then
+ mt = {}
+ setmetatable(_G, mt)
+end
+
+mt.__declared = {}
+
+local function what ()
+ local d = getinfo(3, "S")
+ return d and d.what or "C"
+end
+
+mt.__newindex = function (t, n, v)
+ if not mt.__declared[n] then
+ local w = what()
+ if w ~= "main" and w ~= "C" then
+ print("assign to undeclared variable '"..n.."'")
+ end
+ mt.__declared[n] = true
+ end
+ rawset(t, n, v)
+end
+
+mt.__index = function (t, n)
+ if not mt.__declared[n] and what() ~= "C" then
+ print("variable '"..n.."' is not declared")
+ end
+ return rawget(t, n)
+end