As I'm digging deeper into lua, I'm from time to time looking at the lua C source code itself, to see how something is implemented.
It's nice to see a highly commented code with some quite clear parts which goes right to the point. Quite tough though and dense at many other parts. The whole lua 5.2.2 has a bit more than 14K lines. Not bad for the language, compiler, vm, repl, C Api, and libs.
Anyway, here's a couple of links I found useful in case you want to have a deep look at the lua source: