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

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

Actually, I just got word from a developer I used to work with that this
does the same thing under MicroFocus on Unix.


Davyd Ondrejko wrote:
> 
> 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!


-- 
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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