The Algol 68 program reports an exit status to the operating system once it stops running. The exit status reported by default is zero, which corresponds to success.
= (int status) ¶Procedure that sets the exit status to report to the operating system and immediately stops executing the program. The default exit status is 0 which, by convention, is interpreted by POSIX systems as success. A value different to zero is interpreted as an error status.