Questions were raised about using set! in labs 1, 2, and 3. I replied that I didn't like the apparent intent behind the question but that I wasn't going to look at labs 1 - 3 in any case.

I just looked to see what it would take to eliminate set! from those labs. Without using something like big-bang, which is much more advanced, I don't see how set! can be avoided. Those labs occurred at the start of Realm of Racket when the goal was to find an easy way to introduce the language. The exercise as constructed depends on set! to maintain state. At this point I think that probably was not a good way to introduce the language, but that's what was in the book. So we used it. I would probably do it differently another time.