COBOL OPEN AND CLOSED SUBROUTINES

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COBOL supports open and closed subroutines.

Open subroutinesThey are implemented using the first format of the PERFORM verb.
For example:
PERFORM SUBPREFORM.
...
SUBPROFORM.
COBOL-STATEMENTS
Closed subroutines They are implemented using the CALL verb and contained or external subprograms.
For example:
CALL "SUBPROG"

Open subroutine is not a real routine, it's in fact a instructions block, so instructions GOBACK/STOP RUN/EXIT PROGRAM on a open subroutines work like on main program.

For example: (RED instructions will not be executed)

STOP RUN

       IDENTIFICATION DIVISION.              PROGRAM-ID.    MAINPROG.              ENVIRONMENT DIVISION.                 DATA DIVISION.                        PROCEDURE DIVISION.                       DISPLAY "MAIN ENTRY".           PERFORM PERFORM-SUB.                   DISPLAY "MAIN EXIT".           STOP RUN.       PERFORM-SUB.                       DISPLAY 'SUB ENTRY'.           STOP RUN.             *> PROGRAM STOP HERE           DISPLAY 'SUB EXIT'.

EXIT PROGRAM

       IDENTIFICATION DIVISION.              PROGRAM-ID.    MAINPROG.              ENVIRONMENT DIVISION.                 DATA DIVISION.                        PROCEDURE DIVISION.                       DISPLAY "MAIN ENTRY".           PERFORM PERFORM-SUB.                   DISPLAY "MAIN EXIT".           STOP RUN.       PERFORM-SUB.                       DISPLAY 'SUB ENTRY'.           EXIT PROGRAM.         *> STATEMENT IS IGNORED           DISPLAY 'SUB EXIT'.

(EXIT PROGRAM is ignored)

GOBACK

       IDENTIFICATION DIVISION.              PROGRAM-ID.    MAINPROG.              ENVIRONMENT DIVISION.                 DATA DIVISION.                        PROCEDURE DIVISION.                       DISPLAY "MAIN ENTRY".           PERFORM PERFORM-SUB.                   DISPLAY "MAIN EXIT".           STOP RUN.       PERFORM-SUB.                       DISPLAY 'SUB ENTRY'.           GOBACK.               *> PROGRAM STOP HERE           DISPLAY 'SUB EXIT'.

(GOBACK works as STOP RUN)

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