Exit in CLIPS

Here’s an idiomatic CLIPS example demonstrating the concept of exiting a program:

(deffunction exit-program (?status)
   "Exit the program with the given status"
   (printout t "Exiting program with status " ?status crlf)
   (exit ?status)
)

(defrule main
   (initial-fact)
   =>
   (printout t "Starting program" crlf)
   (assert (perform-exit 3))
)

(defrule perform-exit
   ?f <- (perform-exit ?status)
   =>
   (retract ?f)
   (exit-program ?status)
)

(defrule cleanup
   (declare (salience -100))
   =>
   (printout t "This cleanup will not be executed" crlf)
)

This CLIPS program demonstrates the concept of exiting a program with a specific status code. Let’s break down the code and explain its components:

1. We define a function exit-program that takes a status code as an argument. This function prints a message and then calls the built-in exit function with the given status.

2. The main rule is triggered by the initial fact. It prints a starting message and asserts a fact to perform an exit with status 3.

3. The perform-exit rule is triggered by the fact asserted in the main rule. It retracts the fact and calls the exit-program function.

4. We include a cleanup rule with a low salience (priority) to demonstrate that it won’t be executed when the program exits.

To run this program:

1. Save the code in a file, e.g., exit_program.clp.
2. Load the file into a CLIPS environment.
3. Run the program using the (reset) and (run) commands.

CLIPS> (load "exit_program.clp")
CLIPS> (reset)
CLIPS> (run)
Starting program
Exiting program with status 3

Note that the cleanup rule is not executed because the program exits before it has a chance to fire.

In CLIPS, unlike some other programming languages, there isn’t a built-in way to capture the exit status of a program. The exit function in CLIPS is primarily used to terminate the execution of rules, and the status code is more for documentation purposes within the CLIPS environment.

This example demonstrates how to structure a CLIPS program to exit with a specific status code, which is conceptually similar to the Go example provided. However, it’s important to note that the behavior of exit in CLIPS may differ from other programming languages in terms of how the exit status is handled by the operating system.