The book uses common lisp, so you'll need to know how to read that. Otherwise I think you should be fine. It's not a book about idioms or coding styles, but about thinking in lisp. If the code examples are confusing, it'll be because you're not sure what something means in common lisp or because you're learning new ideas, not because the code is poorly written. So, if you treat it as a book of ideas as opposed to "teach yourself x language in 24 hours", you should be OK :)