From: Stefan Monnier <monnier@IRO.UMontreal.CA>
To: Eli Zaretskii <eliz@gnu.org>
Cc: bruce.connor.am@gmail.com, emacs-devel@gnu.org
Subject: Re: Character group folding in searches
Date: Sun, 08 Feb 2015 09:03:23 -0500 [thread overview]
Message-ID: <jwvzj8ov7a5.fsf-monnier+emacs@gnu.org> (raw)
In-Reply-To: <83bnl5buvm.fsf@gnu.org> (Eli Zaretskii's message of "Sat, 07 Feb 2015 17:31:57 +0200")
> I'm sorry, I don't understand how this will solve the use-cases
> brought up in this thread. Can you explain?
Every equivalence class selected by such a DFA can match any set of
strings that can be described by a regular expression, so it should be
more than sufficiently powerful.
> . exact match -- only exactly the same codepoints match
The DFA is trivial, matches any (and only) one-char sequences and
returns the char.
> . base-character match -- this ignores any combining marks,
> diacriticals, etc.
Admittedly, less trivial since we have to remember the base char after
matching it, while skipping subsequent combining marks and diacriticals.
> . matching ligatures, such as ffi and ffi
Straightforward.
> . ignoring punctuation, like string-collate-equalp does,
> i.e. "foobar" will match "foo.bar"
Easy: the DFA will simply loop back when it sees a ".".
> . ignoring isolated zero-width or non-combining marks and
> directional controls
Same.
> I understand very well how these can be handled by several different
> char-tables, but you seem to say that a single char-table can do all
> this, and I don't see how.
Not sure what you mean by "single char-table" or why you think I said
something about single-vs-multiple char-tables.
A first implementation of DFAs could use internally char-tables (where
each node of the DFA is a char-table) but I think it's something
entirely different from what you mean by "different char-tables" or
"single char-table", since you'd choose one DFA (which may have any
number of char-tables inside).
> Now I'm completely confused: char-tables don't need this optimization,
> as you well know: they already are space-efficient for storing
> characters that map to the table's default value. So I probably
> misunderstand your whole idea, if it does need such an optimization.
A DFA can have hundreds of nodes (hence hundreds of char-tables if we
use char-tables for that), most of which map one or two chars to
a special value while all others are mapped to "the default", so there
can be significant gains from using a more specialized representation.
>> PS: And this same kind of "char-table extended into a DFA" could be
>> useful for syntax-tables in order to provide much more flexible support
>> for multi-character comment markers or "paren-like nested elements".
> If that's your itch to scratch, I'm impatiently waiting for patches ;-)
It's been in the back of my mind for many years.
Stefan
next prev parent reply other threads:[~2015-02-08 14:03 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-02-06 13:04 Character group folding in searches Artur Malabarba
2015-02-06 14:32 ` Eli Zaretskii
2015-02-06 16:18 ` Artur Malabarba
2015-02-06 16:44 ` Eli Zaretskii
2015-02-06 18:03 ` Stefan Monnier
2015-02-06 19:03 ` Eli Zaretskii
2015-02-06 19:27 ` Artur Malabarba
2015-02-06 21:38 ` Eli Zaretskii
2015-02-06 22:08 ` Artur Malabarba
2015-02-07 8:38 ` Eli Zaretskii
2015-02-06 19:41 ` Stefan Monnier
2015-02-06 21:43 ` Eli Zaretskii
2015-02-07 0:05 ` Stefan Monnier
2015-02-07 8:47 ` Eli Zaretskii
2015-02-07 15:02 ` Stefan Monnier
2015-02-07 15:31 ` Eli Zaretskii
2015-02-08 14:03 ` Stefan Monnier [this message]
2015-02-08 19:12 ` Eli Zaretskii
2015-02-09 3:03 ` Stefan Monnier
2015-02-09 15:40 ` Eli Zaretskii
2015-02-09 16:33 ` Stefan Monnier
2015-02-09 17:39 ` Eli Zaretskii
2015-02-10 2:15 ` Stefan Monnier
2015-02-10 15:45 ` Eli Zaretskii
2015-02-07 0:07 ` Juri Linkov
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