Defer in COBOL

In COBOL, we don’t have a direct equivalent to the defer keyword. However, we can achieve similar functionality by using structured programming techniques and ensuring that cleanup operations are performed at the end of a procedure. Here’s how we might structure a similar program in COBOL:

       IDENTIFICATION DIVISION.
       PROGRAM-ID. DEFER-EXAMPLE.
       ENVIRONMENT DIVISION.
       INPUT-OUTPUT SECTION.
       FILE-CONTROL.
           SELECT WORK-FILE ASSIGN TO "/tmp/defer.txt"
           ORGANIZATION IS LINE SEQUENTIAL.
       
       DATA DIVISION.
       FILE SECTION.
       FD WORK-FILE.
       01 FILE-RECORD PIC X(80).
       
       WORKING-STORAGE SECTION.
       01 WS-EOF PIC X VALUE 'N'.
       
       PROCEDURE DIVISION.
       MAIN-PROCEDURE.
           PERFORM CREATE-FILE
           PERFORM WRITE-TO-FILE
           PERFORM CLOSE-FILE
           STOP RUN.

       CREATE-FILE.
           DISPLAY "Creating"
           OPEN OUTPUT WORK-FILE
           IF WS-EOF = 'Y'
               DISPLAY "Error: Unable to create file"
               STOP RUN
           END-IF.

       WRITE-TO-FILE.
           DISPLAY "Writing"
           MOVE "data" TO FILE-RECORD
           WRITE FILE-RECORD.

       CLOSE-FILE.
           DISPLAY "Closing"
           CLOSE WORK-FILE
           IF WS-EOF = 'Y'
               DISPLAY "Error: Unable to close file"
               STOP RUN
           END-IF.

In this COBOL program, we’re trying to emulate the behavior of the Go program that uses defer. Here’s how it works:

1. We define a file in the FILE-CONTROL section and describe its record structure in the FILE SECTION.

2. In the MAIN-PROCEDURE, we perform three operations in sequence: creating the file, writing to it, and closing it. This is analogous to the main function in the Go program.

3. The CREATE-FILE procedure opens the file for output. This is similar to the createFile function in Go.

4. The WRITE-TO-FILE procedure writes data to the file, similar to the writeFile function in Go.

5. The CLOSE-FILE procedure closes the file, which is analogous to the closeFile function in Go that was deferred in the original program.

6. We check for errors after opening and closing the file. If an error occurs (indicated by WS-EOF being set to ‘Y’), we display an error message and stop the program.

While COBOL doesn’t have a defer mechanism, this structured approach ensures that the file is always closed at the end of the main procedure, achieving a similar effect to the Go program.

Running this COBOL program would produce output similar to:

Creating
Writing
Closing

This example demonstrates how to structure a COBOL program to ensure cleanup operations are performed, even though COBOL lacks a direct equivalent to Go’s defer keyword.