On Thu, 6 Dec 2001, Garrett Goebel wrote:
> Maybe Sam Tregar could share some tips on do's and don't of speed
> considerations when writing a grammar. Lessons he's learned rewriting his
> grammar for HTML::Template::Expr.
Hmmmm, I don't know how general my observations are but here goes:
1) Don't use autotree (duh).
2) Rather than breaking out equivalent forms into separate rules combine
them in a regex for a single rule. Ultimately keeping the rule-count
as low as possible seemed to help.
3) Think carefully about the parse tree you want to build - if you don't
need a particular piece of information then don't put it in the tree.
I think this one was of particular importance for
HTML::Template::Expr since it also allows the interpreter to be
faster.
I worked in a strictly trial-and-error mode. I'd make a change and then
run my benchmark. If the time went down I kept the change, if not I'd
hurl curses into the sky and try again.
> I noticed this
> (http://search.cpan.org/doc/TBONE/Parse-RecDescent-FAQ-2.22/FAQ.tt)
> FAQ and thought you all might be interested. It has nice section
> called "OPTIMIZING YOUR GRAMMARS", and lots of other tips.
Interesting, I had no idea that existed! Off to CPAN...
-sam
