I found http://hokstad.com/compiler a lot easier to understand than any other compiler tutorial I've seen. Writing a compiler the way you'd write any other program. It does end up with e.g. a distinct parser, but only when the reasons that might be a good idea become apparent.
Though in retrospect I think it should have been two separate series (and I need to write a few more parts; I'm very close to having it compile itself as of last night).
I think it'd have been better to evolve the initial simple language into an equivalently simple language to parse, and kept the long slog towards compiling Ruby as a separate thing.
Especially as that has complicated things enough to be in severe need of various refactoring (which I'm avoiding until it will compile itself, at which point I'll start cleaning it up while insisting on keeping it able to compile itself..).
The parser itself started out conceptually quite clean, for example, but the Ruby grammar is horribly complex, and I keep having to add exeptions that's turned it quite convoluted. I don't doubt it can be simplified with some effort once I have the full picture, but it's not great for teaching.
