Composite arithmetic on sub-composite elements

[MrDurion]

For the ADD and SUBTRACT statements, we are required to also add composite data, adding sub-elements if they have the same name. However, it is unclear what should happen when the sub-elements are different data structures.

We have 4 cases that can occur, and have assumed behavior for two of them, but we are unsure what should happen for the other two.

• copy composite into composite: recursively do this sub-element addition.
• copy composite into elementary: ??
• copy elementary into elementary: add the two together.
• copy elementary into composite: ??

An example where this would occur:

IDENTIFICATION DIVISION.
    PROGRAM-ID. EXAMPLE.
DATA DIVISION.
    01 A.
    02 C PICTURE OF 99 VALUE 11.
    01 B.
    02 C PICTURE OF 9 VALUE 2.
    02 D PICTURE OF 99 VALUE 33.
    01 E.
    02 C.
    03 Q PICTURE OF 999 VALUE 44.
PROCEDURE DIVISION.
    ADD A TO E.
    STOP

How are we supposed to handle this?

[grammarware]

• All four of your cases start with "copy" but there is no copying going on, ever.
• ADD and SUBTRACT can only work when all the arguments are "elementary" or all arguments are "composite". You can decide to display a warning or error when compiling/interpreting the cases marked with ?? in your question.
• Your example is not grammatically correct:
  • it has PICTURE OF instead of PICTURE IS
  • it includes the VALUE clause which is one of the many clauses in COBOL that do not exist in BabyCobol
  • it also lacks the final dot.
• Your example does not align well with the four categories you speak of.
  • ADD A TO B would be a good example of category 1. It would add C OF A to C OF B and leave D OF B alone.
  • ADD A TO Q would be an example of category 2. Real COBOL compilers will refuse to compile it, complaining that Q is "not a group name".
  • ADD C OF A TO D OF B would be an example of category 3. Should be obvious how that works.
  • ADD Q TO A would be an example of category 4. Again, real compilers stop on an error here.
  • As it stands now, ADD A TO E just takes two data structures and adds its corresponding constituents to each other. Since nothing name-matches within A with anything within E, this statement does nothing. You can opt for displaying a warning if this happens. Real COBOL compilers do not.
• Just as a minor remark: if you indent your data division, it will help presenting the data structures visually, and you will also see better what's happening in your program.