The code allows you to define command line flags using the DEFINE-FLAG macro. For instance, the following form defines a boolean flag called *DEBUG-FLAG* that is set based on the presence of "--debug" in the application's command line.
If the command line contains "--debug" or "--debug=true", then *DEBUG-FLAG* is set to T. Otherwise, it defaults to NIL.
The function PARSE-COMMAND-LINE is used to parse the command line.
The file flag-test.lisp contains more examples.
command-line options parser