Re: PERFORM token (was RE: gnubol: Hacks needed to parse COBOL

[Davyd Ondrejko <david.ondrejko@safelite.com>]

Here's an interesting situation.

>   Bob> In compilers I have seen, the END-PERFORM is required on the
>   Bob> inline perform, but is actually wrong on out-of-line
>   Bob> performs. I defy anyone to detect that correctly. Since rules
>   Bob> have to be concurrently scoped, any out-of-line perform can
>   Bob> quite possibly be scoped internnaly to an inline perform. If
>   Bob> you attempt to trap the END-PERFORM on the end of the
>   Bob> out-of-line perform where it does not belong, then you swallow
>   Bob> the outer inline perform's explicit scope
>   Bob> terminator. Consequently spurious END-PERFORM tokens seem
>   Bob> destined to fly high into the upper rule hierarchy.
> 
> OK, I get the idea, but I still can't share your sense of dread over
> it.  The END-PERFORM is no more a part of the syntax of an
> out-of-line PERFORM than END-EVALUATE is.  Sure, a containing in-line
> PERFORM will be terminated.  Then we'll continue to parse some more
> statements that should have been in the loop or whatever.
> Eventually, we'll get to an END-PERFORM that can't be accepted and
> we'll diagnose it.  In the unlikely case that the programmer has
> applied an END-PERFORM to his out-of-line PERFORM, and omitted the
> one for the containing in-line PERFORM, he has made a programming
> error, but he has written a legitimate COBOL program.

MOVE 0 TO Q.
MOVE 13 TO VARIABLE.
IF VARIABLE > 3
    PERFORM UNTIL Q > 10
        ADD 1 TO Q
        PERFORM THIS-PARAGRAPH THRU THIS-PARAGRAPH-EXIT
    END-PERFORM
    DISPLAY "Q IS NOW = ", Q
END-IF.

In one compiler I've come across (ICHOST under UNIX), depending on the
settings, this will generate a warning or an error.  (Not sure, don't
have access to it at this point.)  The END-PERFORM actually associates
with the out-of-line PERFORM and leaves the in-line PERFORM without any
termination.  If it generates code, then the DISPLAY is executed 11
times.

-- 
David R. Ondrejko - EDI/Referral - Safelite Glass Co.
 Mathematician by training - Programmer by trade - Philosopher by nature
 Genius by genetics - Atheist by conviction - Hedonist by desire!

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