[Haskell-cafe] Re: Efficient parallel regular expressions

[Nicolas Pouillard]

Excerpts from ajb's message of Wed Nov 05 03:59:03 +0100 2008:
> G'day all.

Hi,

> 
> Quoting Achim Schneider <barsoap at web.de>:
> 
> > 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.
> 
> In the case of a command followed by arguments, it would make more
> sense to use a keyword recogniser followed by a command-specific parser.
> 
> One suggestion follows.

Oops there is a bug in there:

GHCI> keywordMatch  [("a", 1), ("aa", 2)] "aa"
Nothing

The third equation of generateTrie' is missing a guard, namely k1 /= k2.

generateTrie' [(k1:ks1,v1),(k2:ks2,v2)] | k1 /= k2
     = Node2 k1 (generateTrie [(ks1,v1)]) k2 (generateTrie [(ks2,v2)])

Best regards,

-- 
Nicolas Pouillard aka Ertai