Similarly to networking, multiple threads of program execution, user-defined streams, among other features, Common Lisp requires non-portable code for exiting the Common Lisp implementation, if possible. This library is a reasonably comprehensive solution and interface to this.
The SHUT-IT-DOWN library was created to serve the author's needs when writing an interactive program that needed to be able to exit.
The design disregards return values for the Lisp process on platforms that have such.
There is no argument and QUIT either succeeds or fails, then returning no value.
Addition to Quicklisp is pending.
Here is the page dedicated to this program.