If Lua did the decent thing and insisted that you declare every variable first, it wouldn't have this stupid problem. Squirrel should probably do it, too. Python certainly should! (Even Javascript, misguided as it is in so many respects, has strict mode!)

This sort of static checking massively increases the amount of code you can look after without going insane. Add static types too, and you're even better off.

(Last time I used Lua, I modified it so that all variables had to be introduced before their first use, either using `local', or a new `global' keyword. More static checks, and no more accidental globals.)