I've enjoyed these first two - they're a good summary of how things are laid out, without getting into too many of the messy details. I miss an explanation of closures, but that'd require lots of messy details, I'm sure.

You might find the way that closures ("upvalues") are implemented in Lua helpful, too. There's a summary in this paper (http://www.tecgraf.puc-rio.br/~lhf/ftp/doc/jucs05.pdf) starting around pg. 8, and the source (http://www.lua.org/source/5.1/) is pretty readable (if somewhat sparsely commented).

Not at all. It's a block: the first value points at the code, the rest of the values are the free variables.