exit-code specifies <exit code> (which must be an integer expression) when the program runs from the
command_line.
exit-code can be specified anywhere in the code, and does not mean exiting the program. To exit the program, either use
exit-request or simply allow
request function to reach its end.
When exit-code is not used, the default exit code is 0.
When the program exits, its exit code will be 12:
exit-code 12
...
exit-request
