From: Carsten Dominik <carsten.dominik@gmail.com>
To: Thorsten Jolitz <tjolitz@gmail.com>
Cc: emacs-orgmode@gnu.org
Subject: Re: [BUG] in org-property-drawer-re?
Date: Tue, 1 Oct 2013 20:44:10 +0200 [thread overview]
Message-ID: <08DC8B04-182A-4B69-A5A7-F4F7A98F621C@gmail.com> (raw)
In-Reply-To: <87mwms4z4o.fsf@gmail.com>
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On 1.10.2013, at 20:36, Thorsten Jolitz <tjolitz@gmail.com> wrote:
> Carsten Dominik <carsten.dominik@gmail.com> writes:
>
>> On 1.10.2013, at 19:50, Thorsten Jolitz <tjolitz@gmail.com> wrote:
>>
>>>
>>> Hi List,
>>>
>>> for the navi-mode keyword-search for complete property drawers I copied
>>>
>>> ,-----------------------
>>> | org-property-drawer-re
>>> `-----------------------
>>>
>>> from org.el:
>>>
>>> #+begin_src emacs-lisp
>>> (concat "\\(" org-property-start-re "\\)[^\000]*\\("
>>> org-property-end-re "\\)\n?")
>>> #+end_src
>>>
>>> #+results:
>>> : \(^[ ]*:PROPERTIES:[ ]*$\)[^\\000]*\(^[ ]*:END:[ ]*$\)
>>> : ?
>>>
>>> A bit unreadable, but you get the message ... here is my hopefully equivalent
>>> version:
>>>
>>> ,--------------------------------------------------------------
>>> | (:propertydrawer
>>> | . (concat "\\(^[\\s\\t]*:PROPERTIES:[\\s\\t]*$\\)[^\\000]*"
>>> | "\\(^[\\s\\t]*:END:[\\s\\t]*$\\)\\n?"))
>>> `--------------------------------------------------------------
>>>
>>> But this did not match correctly in Bernt Hansens tutorial:
>>
>> Indeed, this is a bad regular expression, it is too greedy and will
>> match all the way to the last :END: line it can find. also, \\s is
>> wrong, it should be just a space, so "[ \t]". Luckily
>> this regular expression does not seem to be used in Org as far
>> as I can see....
>
>
> But, if this is equivalent to the #+results: block above, it is defined
> in org.el without that one ? indicated that makes the difference:
>
> ,-----------------------------------------------------------
> | (:propertydrawer
> | . (concat "\\(^[ \\t]*:PROPERTIES:[ \\t]*$\\)[^\\000]*?" <=
> | "\\(^[ \\t]*:END:[ \\t]*$\\)\\n?"))
> `-----------------------------------------------------------
Yes. this is a bug, fortunately inconsequential since org does
its property matching in a different way.
Anyway, this bug is fixed in master.
- Carsten
>
>> Yes, you need the star to make it non-greedy.
>
> the '?' I guess ...
>
>> However, you can leave the \n after you have corrected the
>> character class to "[ \t]" - it just means that
>> the \n will be part of the match, but still allow
>> for the possibility that the last line hits the end
>> of the buffer.
>
> ok, I see
>
>> Ahhhh, regular expressions. I think in my entire history
>> as a programmer, learning about regular expressions was
>> the biggest braintrip I ever had - still love them.
>
> thanks god for M-x regexp-builder ;)
>
>>> PS
>>> Can anybody explain this marvelous construct in the regexp:
>>>
>>> ,---------
>>> | [^\\000]
>>> `---------
>>
>> This is just a cheep way to match any character at all, because \000 should
>> not be part of any string (in C it indicates the end of a string).
>> In principle you could put any character you are sure will not turn up,
>> but \000 seems to be the safest choice. It is
>> faster (I think) than "\\(.\\|\n\\)*" because the first will
>> just run fast and streight with a table lookup while the
>> latter need to always alternate between two alternatives.
>> I have not timed it, though.
>
> This is a very nice trick, and the alternative looks easy too - I have
> to remember this.
>
>>> I often pondered about how to achieve its effect with other means, since
>>> I did not find it in the Emacs Lisp manual.
>>
>> There you go - sometimes a brain is better than the Emacs manual :)
>
> Thanks a lot
>
> --
> cheers,
> Thorsten
>
>
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next prev parent reply other threads:[~2013-10-01 18:44 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-01 17:50 [BUG] in org-property-drawer-re? Thorsten Jolitz
2013-10-01 18:17 ` Carsten Dominik
2013-10-01 18:36 ` Thorsten Jolitz
2013-10-01 18:44 ` Carsten Dominik [this message]
2013-10-02 9:55 ` Nicolas Goaziou
2013-10-02 11:05 ` Carsten Dominik
2013-10-02 11:14 ` Nicolas Goaziou
2013-10-02 11:37 ` Carsten Dominik
2013-10-02 11:38 ` Thorsten Jolitz
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