Hi!
Here are some of my Advent of Code related files using Common Lisp. (All of these are not of the best quality, or how to say it.)
Please, notice that the day-specific input data has not been included.
At the time of writing this (19th of December 2020), Quicklisp has not been used.
I have used LispWorks https://www.lispworks.com/ or SBCL. http://www.sbcl.org/