The source to Lua is quite good, though not commented heavily. There's a roadmap by Mike Pall at http://www.reddit.com/comments/63hth/ask_reddit_which_oss_co... , and some other notes on the Lua users's wiki at http://lua-users.org/wiki/LuaSource . Lua has been kept small for embedding, and its designers are adamant about portability, so the code is very clean. (It's also one of my favorite languages.)
Also, _Modern Compiler Implementation in ML_ by Andrew Appel (http://www.cs.princeton.edu/~appel/modern/ml/) is quite good. It uses SML, but is pretty understandable if you're familiar with OCaml or (perhaps) Haskell. I found it vastly more readable than the Dragon Book.
Also, _Modern Compiler Implementation in ML_ by Andrew Appel (http://www.cs.princeton.edu/~appel/modern/ml/) is quite good. It uses SML, but is pretty understandable if you're familiar with OCaml or (perhaps) Haskell. I found it vastly more readable than the Dragon Book.