Neat, but the video ended too quickly! Is there a follow-up that explains the structure of the lisp implementation? I tried writing it out but don't feel entirely comfortable with the idea that I've understood it fully. Would be great to have the implementation also explained in as much detail.

OP here. This video was just a one-off that was essentially a one-off warm-up for Nathan's class, but I absolutely recommend going through the rest if you're interested in programming languages or want to learn how to write an interpreter or compiler. It was really useful for me and it's totally free at http://nathansuniversity.com

Awesome, thanks for the tip. I guess I'm looking for a good way to get into functional languages and I liked the video because it felt like it was to the point and not loaded with abstractions. I'll def check out the rest of the class!