Man, I can't even tell what this is supposed to be. My confusion is entirely founded. My thought process with articles like this goes something like "C in four functions, huh? Sounds like it could be clever. I'll just click and read the explanation... Oh, there isn't an explanation. Well, maybe this file will explain things! ...Nope, it's 500 lines of mostly-uncommented if-else statements. Maybe it's a compiler? I dunno!"
I'm sure there's a subset of the programming community for whom this is crystal clear on first sight, and that's great; but there's a lot more of us who could probably get the joke with a few hints, so it would be nice if you'd help out instead of declaring that if you understand it, it must be easy.
I hope someone will write an explanation. I'm still working on one for my own (quite different) little compiler.