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Re: emacs 22 - regular-expression isearch on spaces extremely lenient
From: |
ken manheimer |
Subject: |
Re: emacs 22 - regular-expression isearch on spaces extremely lenient |
Date: |
Mon, 1 May 2006 18:04:40 +0000 (UTC) |
User-agent: |
Loom/3.14 (http://gmane.org/) |
Drew Adams <drew.adams <at> oracle.com> writes:
> [Ken Manheimer wrote:]
>
> i recently started noticing that emacs 22 regular expression isearches
> do not treat spaces exactly - any number of spaces in your search will
> map to any number, same or different, of spaces in the target.
>
> can anyone tell me whether or not it's deliberate, and what the
> rationale is?
>
> (setq search-whitespace-regexp nil) will turn this off. When this is nil,
> each space you type matches literally, against one space.
thanks! i did infer that from a bit of investigation (in isearch-search), and
am kinda mortified by how unobvious it is. i agree very strongly with your
analysis, and feel the feature is too elusive in too many ways - all the
questions i was asking: behaviorally ("wait a minute, does it really do that,
and if so, when?"), properness ("is it really supposed to do that?"),
control/inhibition (how the hell do i turn it off?!") - that it's a Real Bad
Idea. oh well.
i agree that making the control obvious, and defaulting it to off, is a much
better way to make the feature available. (i could even see having a transient
message in the minibuffer whenever someone types in a space, saying how to make
it a fuzzy space with Ctrl-Q.)
> `search-whitespace-regexp' is, by default, "\\s-+", which searches for any
> amount of whitespace when you type a space. This was introduced for regexp
> search in Emacs 21, I believe. There is no such "magic-space" searching in
> Emacs 20. Doc:
>
> If non-nil, regular expression to match a sequence of whitespace chars.
> This applies to regular expression incremental search.
> When you put a space or spaces in the incremental regexp, it stands for
> this, unless it is inside of a regexp construct such as [...] or *, + or ?.
> You might want to use something like "[ \t\r\n]+" instead.
> In the Customization buffer, that is `[' followed by a space,
> a tab, a carriage return (control-M), a newline, and `]+'.
i didn't notice anything about it in the documentation for isearch, though now
that i look at the section on regular expression search i see something about
it. this is a pitfall of rich features - too much functionality to describe
adequately without overwhelming.
> The rationale was, I believe, that some users might want that: type space to
> find any amount of whitespace, in particular, to find two words that are
> separated by a newline.
i would have suggested using "\ " or "^Q " (which both currently now have the
opposite effect).
> There was talk of using this "magic-space" searching also for plain
> incremental search in Emacs 22, but I don't think that was done.
good.
> FWIW, I agree with Miles on this - this is a misfeature, if turned on by
> default. It should be off by default, and you should be able to turn it on
> via a simple toggle during incremental search (regexp or plain).
who's miles?
> Here is what I wrote 2005/02/06 to emacs-devel on this:
>
> > > sometimes the actual whitespace matters.
> > Right: in *regexp* search.
> while people generally expect regexp searches to be a bit
> fuzzy, they might expect a non-regexp search to be exact.
> Since the fuzzy whitespace matching often "looks" like normal
> matching (because the majority of whitespace is in fact a
> single space), it might take some time to see what's going on,
> resulting in some subtle errors. This is particularly true if
> one embeds a search inside a keyboard macro [which I often do].
>
> Plain (incremental) search should be a literal search. Regexp
> search should rigorously respect the regexp. People don't expect
> either to be fuzzy.
>
> The question is "Under what circumstances should typing a space be
> interpreted as wanting to search for any amount of whitespace?"
>
> This is unrelated to both plain search and regexp search. You
> might or might not want this _input effect_ with either plain
> or regexp search.
>
> This is akin to word search (as I think someone mentioned).
> Ultimately, a word search or a space-means-whitespace search is
> implemented with a regexp search - but the point in both cases
> is to provide a user-friendly way to do it, instead of requiring
> users to know about regexps.
>
> By default, neither `C-M-s' nor `C-s' should respect the
> user-friendly space-input feature. Or, rather, the default
> behavior of each should be determined by a user option - a la
> case-fold-search. And, regardless of the value of this option,
> you should be able to toggle space-means-whitespace
> searching from both `C-M-s' and `C-s', via a key sequence.
>
> The question then becomes how to toggle this space-means-whitespace
> searching?
thanks much for the thorough answer - it's good to have the mystery settled,
even if i don't agree with the situation. at least i now know various ways to
work around it...
(i guess it's too late to propose inverting the mode of the feature on
emacs-devel? i'd just copy this posting over there, asking if it's worth
reopening the discussion. i wouldn't want to do that, though, if the discussion
ended on a conclusive pronouncement that even dismissed revisiting in the event
of complaints...)
ken manheimer
http://myriadicity.net
- Re: emacs 22 - regular-expression isearch on spaces extremely lenient,
ken manheimer <=