Needless to say, if this guy is fudging Racket, I am not sure what we can say about the rest of us and what we do with the language. Haha.
EDIT: Was the author, it seems he passed it off to another Racketer now that he is busy with other stuff. Should have clicked the link before posting.
The reader (lexer and parser) turns the source program into syntax objects. The main idea is to make a Racket macro for each Pascal construct. The Racket macro expands into normal Racket.
While I was reading this I realized just about any scheme implementation could probably override their `read` like this as well. Obviously racket as an implementation has focused on making this work well.