[jballanc]

Very well played! If I were the nitpick-y type ;) I'd wonder whether use of the debug library is kosher (esp. in production code), but you are definitely correct. Though, actually, this again correlates very closely with C/Scheme -- You can use an offset from a stack frame pointer to access stack variables in a function scope in C; and upvalues are just closed-over variables a la Scheme closures.

Actually, that's another point in Lua's favor. The mechanism Lua uses for managing closed-over variables is WAY more elegant than, for example, Ruby's mechanism...