Store the environment in "global" table. Make a new environment. Point the __index of the new environment at the global table. Make __newindex of the new enviro

Store the environment in "global" table. Make a new environment. Point the __index of the new environment at the global table. Make __newindex of the new environment a function that throws an error. Congradulations, you have metaprogrammed lua to only set globals explicitly. Good job!