Constructing protected environments

[Jorge Visca <jvisca@...>]

Hi to everyone.

My (lua) program gets a chunk trough the network, and loads it with
loadstring. I provide a set of functions for this piece of code, and i
want to  call some  functions  it declares. PiL recommends building a
protected environment for those cases. I guess it must be done using
scoping and redefining variables, and I was wondering what's the correct
method for that.
Is there a good example somewhere?

Thanks in advance,

Jorge