From: Helmut Eller <eller.helmut@gmail.com>
To: help-gnu-emacs@gnu.org
Subject: Re: how to use parsing expressing grammar
Date: Sun, 21 Dec 2008 10:49:44 +0100 [thread overview]
Message-ID: <m2skohoo1z.fsf@gmail.com> (raw)
In-Reply-To: 91fa65a0-a7e7-4374-8f96-5786c8908615@w24g2000prd.googlegroups.com
* Xah Lee [2008-12-20 22:41+0100] writes:
> I have another question, hopefully this one is not a dumb one.
>
> In summary, if i have
>
> (imgTag "<img" whitespace (+ attributes whitespace) ">")
>
> how to tell PEG that if a attribute is the last item, then the
> whitespace following it is optional?
Hmm, good question. Perhaps something like
(imgTag "<img" (+ whitespace attribute) (opt whitespace) ">")
This does a bit of backtracking, but easy to read.
>> So far only 2 people asked questions. If there are some more we can set
>> up a mailing list.
>
> I'm pretty sure if you create it, more and more people will join it.
> I'm very interested in PEG and think it is of critical importance.
I'll try to set up project at savannah.
> If say emacs 24 has it built in as C code, with all its regex
> functions such as search-forward-regexp, query-replace-regexp etc
> having PEG version, it would make emacs a killer app.
I don't think that PEGs are easy to use interactively, like
query-replace-regexp. Regexps have a more concise notation, which is
crucial when used interactively.
> From Wikipedia, it appears that people have already wrote PEG lib for
> most major langs. There is already a C lib for PEG. The problem with
> them is that most comes with a background of computer lang parsing, as
> opposed to practical use for text processing like regex. (note: regex
> itself came from computer science background as a way to determine
> languages with âregularâ grammar, but today it is far
> removed from theoretical parsing. The process of this transmutation
> took i think 10 years, and it took another 10 or so years until it
> become a widely popular tool in langs, starting with Perl in the
> 1990s) I don't forsee that in the next 10 years that practicing
> programers will all know about computer science of parsing or that
> major langs will all have formal grammar spec. I'm pretty certain
> people are already seeing the potential of PEG as regex replacement
> and working towards creatings such practical goal.
I think that the Lua language uses PEGs for text processing and
apparently implements it's regexp library on top of PEGs.
Helmut.
next prev parent reply other threads:[~2008-12-21 9:49 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <6b8a1070-1a89-48b0-9287-343b673b5758@a29g2000pra.googlegroups.com>
[not found] ` <m27i5yygi5.fsf@gmail.com>
[not found] ` <m2k59ywtj2.fsf@gmail.com>
[not found] ` <b3203a8b-324f-440f-98a9-653c8d582c7c@y1g2000pra.googlegroups.com>
2008-12-20 8:42 ` how to use parsing expressing grammar Xah Lee
2008-12-20 9:34 ` Helmut Eller
2008-12-20 21:41 ` Xah Lee
2008-12-21 9:49 ` Helmut Eller [this message]
2009-03-03 17:34 ` Leo
2009-03-03 17:59 ` Mike Mattie
[not found] ` <mailman.2299.1236115586.31690.help-gnu-emacs@gnu.org>
2009-03-03 22:05 ` Xah Lee
2009-03-03 23:52 ` W Dan Meyer
2009-03-04 0:35 ` Miles Bader
2009-03-05 6:55 ` Mike Mattie
2009-03-05 6:18 ` Mike Mattie
2009-03-05 16:38 ` Mike Mattie
2009-03-06 8:53 ` Helmut Eller
2008-12-20 22:27 ` Xah Lee
2008-12-21 11:24 ` Helmut Eller
2008-12-23 23:21 ` ashishnkadakia
2008-12-17 11:53 Xah Lee
2008-12-18 3:43 ` Kevin Rodgers
[not found] ` <mailman.3007.1229571828.26697.help-gnu-emacs@gnu.org>
2008-12-18 9:24 ` Xah Lee
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