Re: Finding end of sentence[ was Re: Understanding ... Sentence Boundaries]

[Eric Abrahamsen <eric@ericabrahamsen.net>]

Eric Abrahamsen <eric@ericabrahamsen.net> writes:

> ken <gebser@mousecar.com> writes:
>
>> On 12/12/2012 02:02 AM Eric Abrahamsen wrote:
>>> ken<gebser@mousecar.com>  writes:
>>>
>>>> On 12/11/2012 07:03 AM Eric Abrahamsen wrote:
>>>>> ken<gebser@mousecar.com>   writes:
>>>>>
>>>>>> On 06/26/2010 11:05 PM Deniz Dogan wrote:
>>>>>>> 2010/6/27 ken<gebser@mousecar.com>:
>>>>>>>>
>>>>>>>> On 06/26/2010 06:53 AM Paul Drummond wrote:
>>>>>>>>> Thanks for the responses guys.
>>>>>>>>>
>>>>>>>>> ....
>>>>>>>>>
>>>>>>>> Is it possible to specify word boundaries for a particular mode?
>>>>>>>>
>>>>>>>
>>>>>>> Yes, it's part of the syntax table. See e.g. `modify-syntax-entry'.
>>>>>>
>>>>>> Thanks for the pointer to that function.
>>>>>>
>>>>>> The behavior I see in need of repair is the role of so-called "comments"
>>>>>> in sentence syntax.</tag>    For instance, immediately before this
>>>>>> sentence are two spaces... which should signify the end of the
>>>>>> previous sentence.  But functions like "forward-sentence" and
>>>>>> "fill-paragraph" and "backward-sentence" don't recognize it.
>>>>>>
>>>>>> Said another way, the "</tag>" string obscures the relationship
>>>>>> between the period before it and the two spaces after it and so fails
>>>>>> to see that one sentence ends and another starts.  This occurs in
>>>>>> text-mode and seems to be inherited by other modes.
>>>>>>
>>>>>> If I'm reading "modify-syntax-entry" correctly, the default meanings
>>>>>> of '<' and'>' are, respectively, beginning and end of comment, so
>>>>>> modifying them wouldn't fix this problem.  Or can this be remedied by
>>>>>> a change in the syntax table?  Or is this a bug?
>>>>>
>>>>> For this particular case, I think you can modify the value of the
>>>>> `sentence-end' variable (which is returned by the `sentence-end'
>>>>> function? The whole thing is a little confusing). You'd probably be best
>>>>> off starting with the docstring for the sentence-end function, and
>>>>> working back from there.
>>>>>
>>>>> I think the `sentence-end' variable is automatically buffer-local, which
>>>>> means if you change it in a mode-hook it ought to work the way you want.
>>>>> I agree that the whole syntax thing feels like a very well-polished
>>>>> hack.
>>>>>
>>>>> E
>>>>
>>>> Eric,
>>>>
>>>> Yes, that would be the variable to adjust.  I took a hard look at it
>>>> and discussed it (I believe) on this list years ago, but never came up
>>>> with a fix.  As I see it, there are two problems:
>>>>
>>>> First, "one" of the items in that RE would need to be "zero or more
>>>> consecutive instances of '<' followed by any number of other
>>>> characters up until the next '>' is found."  E.g., the RE would need
>>>> to be able to find the end of this
>>>> sentence</b></i>.)</q></p></span></div>   Though I've used REs
>>>> successfully in quite a few instances and so with a small bit of help
>>>> could probably figure that part out, there's a second issue.
>>>>
>>
>> [In my original post the paragraph below was unclear.  So changed it.]
>>
>>>> My considered opinion is that in the above and similar examples, the
>>>> end of the sentence is immediately after the period ('.')... or
>>>> question mark, exclamation mark, etc. and not after the</div>.  That
>>>> is where the point should go when forward-sentence is executed.  This
>>>> means that no RE would work because, once it finds the RE-defined
>>>> sentence-end, it then needs to go backwards within the found string
>>>> until it encounters [.!?]+ and then move the mark one char forward to the
>>>> character after.  IOW, unless I'm missing some capability of REs,
>>>> "sentence-end" needs to be a function rather than an RE and would be a
>>>> different function than one which finds the beginning of a sentence.
>>>
>>> I'm getting way out of my depth here, both regarding regexps and emacs'
>>> sentence-related shenanigans, but you could consider advising the
>>> `sentence-end' function so that it checks current the major mode, and
>>> delegates to a different sentence-end function depending on the mode (or
>>> declines to handle and bails to the built-in sentence-end).
>>>
>>> The individual mode-specific sentence-end functions look at the text
>>> after point, and return a different regexp every time, one specifically
>>> tailored to this particular sentence in this particular mode. The call to
>>> `forward-sentence' or whatever happily uses a different regexp every
>>> time it is called.
>>>
>>> Feels hacky, but I guess `sentence-end' is already doing this in a
>>> sense -- potentially returning a different regexp every time.
>>>
>>> My brain is exhausted!
>>>
>>> E
>>
>> If one were to write a mode-specific replacement for the existing
>> "forward-sentence" and "sentence-end", what are some ways in elisp to
>> ensure that they're invoked when working in that mode?  Would it be
>> enough to include (the recoded) "forward-sentence" and "sentence-end"
>> in the code for that mode...?  or would some kind of specific hook
>> language need to be included in ~/.emacs?
>
> I was considering overloading the `sentence-end' function in a
> mode-hook, but I think it's highly likely that you'd end up polluting
> other modes. So probably the safest thing to do is to advise it at the
> top level, ie in your ~/.emacs file, and then check current mode from
> there. Something like the following totally untested code:
>
> (defadvice sentence-end (before my-check-sentence-end activate)
>   "Possibly short-circuit the `sentence-end' function."
>   (cond ((derived-mode-p 'emacs-lisp-mode)
> 	 (emacs-lisp-sentence-end))
> 	((derived-mode-p 'some-other-mode)
> 	 (other-mode-sentence-end))
> 	(t ad-do-it)))

I'm in the habit of using `derived-mode-p' but on second thought, you'll
probably just want to go with the simpler, but more exacting: (eq
major-mode 'emacs-lisp-mode)