ALTER statement

Remarks#

The much beloved ALTER statement. Changes the target of a GO TO paragraph.

No longer part of the COBOL standard, still supported by many compilers for reasons of backward compatibility. (The syntax diagram is dimmed to show that this is no longer standard COBOL).

A contrived example using ALTER

 identification division.
 program-id. altering.
 date-written. 2015-10-28/06:36-0400.
 remarks. Demonstrate ALTER.

 procedure division.
 main section.

*> And now for some altering.
 contrived.
 ALTER story TO PROCEED TO beginning
 GO TO story
 .

*> Jump to a part of the story
 story.
 GO.
 .

*> the first part
 beginning.
 ALTER story TO PROCEED to middle
 DISPLAY "This is the start of a changing story"
 GO TO story
 .

*> the middle bit
 middle.
 ALTER story TO PROCEED to ending
 DISPLAY "The story progresses"
 GO TO story
 .

*> the climatic finish
 ending.
 DISPLAY "The story ends, happily ever after"
 .

*> fall through to the exit
 exit program.

With a run sample of

prompt$ cobc -xj -debug altering.cob
This is the start of a changing story
The story progresses
The story ends, happily ever after

prompt$ COB_SET_TRACE=Y ./altering
Source:     'altering.cob'
Program-Id: altering         Entry:     altering               Line: 8
Program-Id: altering         Section:   main                   Line: 8
Program-Id: altering         Paragraph: contrived              Line: 11
Program-Id: altering         Statement: ALTER                  Line: 12
Program-Id: altering         Statement: GO TO                  Line: 13
Program-Id: altering         Paragraph: story                  Line: 17
Program-Id: altering         Paragraph: beginning              Line: 22
Program-Id: altering         Statement: ALTER                  Line: 23
Program-Id: altering         Statement: DISPLAY                Line: 24
This is the start of a changing story
Program-Id: altering         Statement: GO TO                  Line: 25
Program-Id: altering         Paragraph: story                  Line: 17
Program-Id: altering         Paragraph: middle                 Line: 29
Program-Id: altering         Statement: ALTER                  Line: 30
Program-Id: altering         Statement: DISPLAY                Line: 31
The story progresses
Program-Id: altering         Statement: GO TO                  Line: 32
Program-Id: altering         Paragraph: story                  Line: 17
Program-Id: altering         Paragraph: ending                 Line: 36
Program-Id: altering         Statement: DISPLAY                Line: 37
The story ends, happily ever after
Program-Id: altering         Statement: EXIT PROGRAM           Line: 41
Program-Id: altering         Exit:      altering
prompt$

See https://open-cobol.sourceforge.net/faq/index.html#alter for more details.