Install cl-fad by entering the following commands in the terminal:
sudo apt update sudo apt install cl-fad
portable pathname library for Common Lisp
CL-FAD (for "Files and Directories") is a thin layer atop Common Lisp's standard pathname functions. It is intended to provide some unification between current CL implementations on Windows, OS X, Linux, and Unix. Most of the code was written by Peter Seibel for his book Practical Common Lisp.