Lua is a free and open-source multi-paradigm programming language released under the MIT license. Created in 1993 by Roberto Lerusalimschy, Luiz Henrique de Figueiredo and Waldemar Celes, Lua is a ...

That code is from “Programming in Lua by Roberto Ierusalimschy, which was written for Lua 5.0. Now Lua is at version 5.1, that work is a little out of date but still useful as a starting point.