Re: Macro aborts even though regexp instance exists - Serious Bug

[dkcombs@panix.com (David Combs)]

In article <mailman.11579.1351050855.855.help-gnu-emacs@gnu.org>,
Kevin Rodgers  <kevin.d.rodgers@gmail.com> wrote:
>On 10/22/12 2:40 PM, Swami Tota Ram Shankar wrote:
>> Hi emacs users,
>>
>> I write a simple macro which works, however, it fails in a particular
>> case.
>>
>> C-s
>> M-r
>>
>> to get into isearch-forward-regexp
>>
>> and give a regexp like
>>
>> ONE\|TWO
>>
>> It works for every TWO and ONE as long as there is a ONE ahead of TWO.
>> In the last instance, no ONE exists after TWO and it fails.
>>
>> \|<=>  OR or disjunction.
>>
>> Any solutions?
>>
>> This is such a fundamental issue that I think its a bug. When the C-s
>> M-r  is used outside the macro definition, the cursor gladly returns
>> to the original position when OR is entered and proceeds forward from
>> there, but perhaps, the macro aborts.
>
>It is not a bug: when ONE fails to match the buffer, C-s (which is designed
>for interactive use, obviously) signals an error, which terminates the macro
>execution.
>
>That's because there is no way for C-s to know that you _might_ type \|TWO
>after ONE.
>
>So the solution is to make sure that the regexp is not complete after ONE:
>C-s \(ONE\|TWO\)
>
>> I guess, this can lead to a lot of confusion and time wastage, if the
>> user is unaware of this and most likely to neglect it because its
>> contrary to normal usage.
>
>Yes, there is a lot of confusion and wasted time when a user is not aware
>of how to use a program.
>
>> I include more newsgroups because of the seriousness of this bug.
>
>Whatever :-)
>
>-- 
>Kevin Rodgers
>Denver, Colorado, USA
>
>

(1) THANKS FOR THAT HINT/WARNING/INFO!

(2) "when a user is not aware of how to use a program": I don't know
    that this thread really falls under that.  Although your solution
    and especially the reason for it "obvious" -- but only once you've
    seen it.  It's actually a little subtle.

    AND I believe it's so important (and easy to get wrong) that
    it should be added to the emacs manual (in macros) AND to
    any much-used cheat-sheets -- plus the wiki, of course.

    Perhaps you (as one of the real gurus around here) could write
    a paragraph and example and ask the developers to put it into
    the right places.

Thanks again for the pointer!

David