[Haskell-cafe] Re: Efficient parallel regular expressions

"Dan Piponi" wrote:

On Tue, Nov 4, 2008 at 9:26 AM, Achim Schneider wrote:

...

Martijn van Steenbergen wrote: For anything remotely connected to parsing, always use parsec.

I'd not be surprised if the beast is touring complete in itself...

Actually, this can count against you. It's very easy to use Parsec to build an innocent looking grammar that's too slow to use because it'll do all kinds of backtracking to find a way to make your input fit the grammar. I recommend Parsec for lots of tasks, but take care to design the grammar so it doesn't take exponential time to do anything.

Considering that he's talking about a mud, I figure the grammar is a quite straightforward command = l[eft] | r[ight] | ... | t[ake] <item> | c[ast] <spell> That is, I'd be very surprised if you even need more than two or three characters lookahead, much less backtracking. Parsec is a thousand times more efficient for such things than regular expressions, and you can just lazily parse all the input into a list of data constructors and happily fold it into your state... The only thing more straightforward than this is reading a xml with HaXML (if you have a DTD, that is) -- (c) this sig last receiving data processing entity. Inspect headers for copyright history. All rights reserved. Copying, hiring, renting, performance and/or quoting of this signature prohibited.