Re: Lua and LPeg

[Patrick Donnelly <batrick () batbytes com>]

On Fri, Mar 5, 2010 at 2:23 PM, David Fifield <david () bamsoftware com> wrote:
> On Mon, Mar 01, 2010 at 01:53:14PM -0500, Patrick Donnelly wrote:
> > On Mon, Mar 1, 2010 at 3:35 AM, Martin Holst Swende <martin () swende se> wrote:
> > > Yes and no. I took a quick look at what libraries existed, but license
> > > issues (of which I am no expert) and/or overly complicated behaviour put
> > > me off. For example, the luaforge-library is 10+files (not counting
> > > testcases) and, in addition, requires Lpeg, a complete library for
> > > parsing grammar. Had Json been a lot more complex than it actually is,
> > > that perhaps had seemed the best solution. That being said, other
> > > implementations may be better than mine, and if you have any suggestions
> > > once you have looked at the code they are most welcome.
> >
> > Well, the luaforge library is MIT licensed (same as Lua) so no problem
> > there. The library itself is modularized into files which is good and
> > bad, mostly good when it comes to LPeg. My feeling on LPeg is that
> > Nmap will eventually have it because Lua will eventually have it.
> > Plus, LPeg is appropriate for most parsing problems (JSON fits nicely)
> > that are network related. What we are waiting for is a library/script
> > that heavily relies on it that justifies the addition of LPeg. The
> > JSON library may have been that library :)
>
> LPeg is planned to be in a future release of Lua, right? Then I think we
> should wait for that so that someone else is maintaining it. I admit
> that it is cool technically and I am interested in learning more about
> it.

Well, it is highly probable but it could be quite a while before that
happens. Roberto gives us a maybe [1] but definitely not for Lua 5.2.
I don't think it is prudent for us to wait for Lua to officially add
it because that version will likely be many years away due to Lua's
release cycle [2].

About maintaining it, Roberto (author of Lua) is developing LPeg so
there should be no worries about that.

I think if we wanted to add it now we could improve a lot of libraries
as well as NSE. I believe I showed you the script args code
implemeneted in LPeg and the improvement in readability and code size
(58 -> 20 lines, not including extraneous newlines) was quite good
(attached). I'm fairly certain libraries like the http or json library
would benefit as well.

[1] http://lua-users.org/lists/lua-l/2008-02/msg00724.html
[2] http://www.lua.org/versions.html

-- 
- Patrick Donnelly

Attachment: sargs-lpeg.patch
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