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

[ken]

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?