Strict mode in LUA

strict.lua

-- The strict() function helps catch common Lua programming errors
-- by detecting uses of undefined variables. This is helpful because
-- Lua normally creates global variables silently when you mistype
-- a variable name, which can lead to hard-to-find bugs.
function strict()
	local declared_globals = {}

	-- In Lua, _G is a special table that holds all global variables
	-- setmetatable lets us intercept attempts to read or write globals
	setmetatable(_G, {
		-- This function is called when code tries to create a new
		-- global variable. We make it throw an error instead of
		-- silently creating the variable.
		__newindex = function(_, name, value)
			if not declared_globals[name] then
				error("Attempt to create global variable '" .. name .. "'", 2)
				end
				rawset(_G, name, value)
			end,
		-- This function is called when code tries to read a global
		-- variable. We log a warning if the variable doesn't exist.
		-- Note: We can't crash here because TIC-80 constantly checks
		-- for certain global functions it needs to run.
		__index = function(_, name)
			if not declared_globals[name] then
				trace("Attempt to access undeclared global variable '" .. name .. "'", 2)
			end
			return nil
		end
	})
end

function TIC()
  -- Will throw if strict is enabled
  x = 3
end

function BOOT()
	-- Enable strict mode
	strict()
end