I actually wrote a FFT in LISP as a class project.
Yes I was once insane! .... but I got better!
Wasn’t LISP a bit like a forbidden pleasure? I haven’t used it in 25 years, but I still think of it fondly.
You should get sick again - its fun as an adult, ability to program, the internet with all the videos, and your experience as an adult(making/losing money investing, slamming on the brakes in your car) All those weird pattern things your subconscious tells you some underlying pattern become accessible and as an adult you have a chance of having some perspective to understand why and the wisdom to know what to do with it.
Man an FFT in lisp is cool and would be easy to use as an adaptive filter bank to use to experiment with. Good times to be had!