Re: [open-cobol-list] How does Cobol parse the Procedure Division ?

[Wim Niemans]

A "normal" compiler should issue a warning that you have not reachable code 
after a goto.
In this case there is a independent sentence saying "GO TO C-020.".

That having said, I would be terribly interested in a parser for the data 
division. It is of incredible use to me.

Wim

Op 25 sep. 2013, om 15:15 heeft Dave Stratford het volgende geschreven:

> 
> Patrick wrote:
>> Hi Everyone
>> 
>> It's easy to see how Cobol can be parsed in all of the parts outside of
>> the PROCEDURE DIVISION, statements end with periods.
>> 
>> I can't see how the compiler could understand what is going on in
>> PROCEDURE though. Every language I know of has some sort of character to
>> end a statement. It might be a non printable character but it's there.
>> 
>> PROCEDURE ends in a period and paragraphs end in periods but if we have
>> a statement like this:
>> 
>> MOVE foo TO moo
>> 
>> I could see how the compiler would implicitly know that it ends one
>> token after TO but we can also have:
>> 
>>  MOVE foo TO moo koo boo
>> 
>> Does the next reserved word that is not a part of the current sentence
>> signify an end to the current statement and the final period indicate
>> that there are no further statements coming ?
>> 
>> If this is true, was it always this way. From what I understand it was
>> not.
>> 
>> If this is true did it dramatically increase the complexity of the
>> compiler?
>> 
>> Thanks
> Patrick,
> 
> Full stops vs END-xxx changed at cobol 85. Cobol 74, and earlier, only has
> full stops, while END-xx were added at 85.
> 
> Both have advantages and disadvantages.
> 
> Imagine:
> 
> IF A = B
>   IF A > C
>      MOVE 1 TO X
>   ELSE
>      MOVE 1 TO Y
>   MOVE 1 TO Z
> 
> 
> Where does the final MOVE 1 to Z belong? What happens if you want the ELSE
> to be part of the IF A = B?
> 
> When you ONLY had full stops, put a stop after the Y and the final move was
> independant of the IF's. Put it after the Z and it becomes part of the Z.
> An END-IF allows the programmer to be much more specific and flexible
> about things like this.
> 
> An END-ADD, for example, is really only of use when you also use the ON
> OVERFLOW clause, which is why there is no END-MOVE, there is no ON OVERFLOW
> or equivalent. (I don't think!)
> 
> At work I use a version of Cobol 74, so I don't have the END-xx, but it
> does mean I have to be a lot more careful about what I need to do.
> 
> Personally I prefer full stops as it does mean I have to be a lot more
> precise, but there are cases when I would have liked to have had the
> inline perform that isn't available in cobol 74.
> 
> That said, only yesterday, I had the following:
> 
> C-010.
>    MOVE I1-PROP-NO              TO I4-PROP-NO.
>    OBTAIN ANY R04-PROPERTY USING K4-PROP-NO
>           ON DB-REC-NOT-FOUND
>              DISPLAY "NO R04-PROPERTY FOR " I1-PROP-REF
>                      " CUSTOMER REF " I1-ACC-REF.
>              GO TO C-020.
> 
>    MOVE I4-POST-CODE            TO FAA-POST-CODE.
> 
>    WRITE FAA-EXT-REC.
> 
>    ADD 1                        TO WC-WRITE-COUNT
>                                    WC-CHECKPOINT-COUNT.
> 
> C-020.
>    IF WC-CHECKPOINT-COUNT NOT < WY-CHECKPOINT-LIMIT
>       PERFORM Z-TAKE-CHECKPOINT.
> 
> Can you work out why my program eventually fell over with a page lock
> table full error and an empty output file?
> 
> Took me narly an hour and I lost even more hair!!!
> 
> If anyone is interested, and I can find it, I had a cobol program that
> parses cobol programs to ensure they met the site coding standards of the
> site I was then working on. I myself wrote the data division parser. It's
> written in cobol 74, and parses cobol 74 programs. It would have found
> this fault.
> 
> Dave
> 
> 
> 
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