Re: Infinite Loops and Explicit Exits

From: Joe Zitzelberger (joe_at_zitzelberger.net)
Date: 11/05/04 

Date: Fri, 5 Nov 2004 08:33:03 -0500

On 2004-10-29 15:01:03 -0400, "Chuck Stevens"
<charles.stevens@unisys.com> said:

> For those who have been following the "perform forever" and "exit perform
> [cycle]" threads, I'm just tidying up the first drafts of two proposals that
> I hope to submit Real Soon Now to INCITS/J4 for evaluation and consideration
> for a future standard, if nothing else so that they can be added to the
> "candidates list" for future consideration.
>
> One of these proposals relaxes the current restriction that an EXIT PERFORM
> or EXIT PERFORM CYCLE statement may only appear within a PERFORM ...
> END-PERFORM range.
>
> The other proposal is for PERFORM ... UNTIL FALSE. I didn't want to add a
> new reserved word and for that reason rejected PERFORM ... FOREVER. I was
> concerned about the potential semantic ambiguities that one might encounter
> in sequences like "PERFORM ... PERFORM ... UNTIL EXIT PERFORM ...
> END-PERFORM ...", which led me away from PERFORM ... UNTIL EXIT. I don't
> care for PERFORM ... WITH NO TEST because it really doesn't convey the sense
> of iteration. I am not wedded to the syntax I chose, but I think the
> technical reasons for avoiding the other three here presented are sound.
>
> Unless WG4 so directs, these capabilities can't be included in the proposed
> 2008 standard. But I can envision no technical barrier at all to the second
> of these, and the only barriers I can envision to the first are
> implementor-specific, WG4 *might* acquiesce so long as the additions do not
> cause a delay in the production of that next standard.
>
> At the very least this action on my part will ensure that these topics are
> on the standards committees' radar screens, and stimulate the discussion and
> clarification as to why EXIT PERFORM (with or without CYCLE) was limited to
> inline PERFORMs in the 2002 standard.
>
> -Chuck Stevens

I'm not sure I understand the perform/forever need. In all cases, one
will eventually have to have a conditional check with an "exit perform"
statement. My experience tells me that such a perform can always be
restructured to make that condition the UNTIL clause.

I would like to see a positive perform, sort of a perform/while that
executes until a condition becomes false -- is this what you mean by
PERFORM/UNTIL FALSE? I'm all for it.

Relevant Pages

  • Re: Infinite Loops and Explicit Exits
    ... As the person who wrote the initial proposal to add EXIT PARAGRAPH/SECTION ... Currently the EXIT PARAGRAPH/SECTION syntax can cause VERY unexpected results if ... > For those who have been following the "perform forever" and "exit perform> " threads, I'm just tidying up the first drafts of two proposals that> I hope to submit Real Soon Now to INCITS/J4 for evaluation and consideration> for a future standard, if nothing else so that they can be added to the> "candidates list" for future consideration. ... > One of these proposals relaxes the current restriction that an EXIT PERFORM> or EXIT PERFORM CYCLE statement may only appear within a PERFORM ... ...
    (comp.lang.cobol)
  • Infinite Loops and Explicit Exits
    ... for a future standard, if nothing else so that they can be added to the ... One of these proposals relaxes the current restriction that an EXIT PERFORM ... or EXIT PERFORM CYCLE statement may only appear within a PERFORM ... ...
    (comp.lang.cobol)
  • Re: If you were inventing CoBOL...
    ... I can't get COBOL to produce a *floating* version of the most common ... EXIT PARAGRAPH and EXIT SECTION provide good support for structure ... disallowed in other contexts in the '02 standard. ... EXIT PARAGRAPH and EXIT SECTION are big helps here. ...
    (comp.lang.cobol)
  • Re: Is it possible to use the value of the PROGRAM ID within the source code?
    ... This was used by some compilers to generate null code that ... I can't recall a mandatory EXIT, even on the earliest IBM compilers. ... >paragraph without a statement until the '74 standard. ... During meetings to formulate a Programming Standard, ...
    (comp.lang.cobol)
  • Re: Infinite Loops and Explicit Exits
    ... 04-0195 -- Provide Explicit Infinite Loop Capability ... for a future revision of the standard. ... > One of these proposals relaxes the current restriction that an EXIT ... > or EXIT PERFORM CYCLE statement may only appear within a PERFORM ... ...
    (comp.lang.cobol)