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From: worley@compass.com (Dale Worley)
Newsgroups: comp.lang.perl
Subject: Sluggish patterns.
Message-ID: <1991Apr1.181801.16850@uvaarpa.Virginia.EDU>
Date: 1 Apr 91 18:18:01 GMT
Sender: mmdf@uvaarpa.Virginia.EDU (Uvaarpa Mail System)
Reply-To: worley@compass.com
Organization: The Internet
Lines: 44


   X-Name: Felix Lee

   I have a pattern /$cookie/ that appears in an inner loop and gets
   evaluated thousands of times.  Recompiling the pattern every time is
   terribly inefficient, since $cookie almost never changes.

   Well, here's the original loop:
	   while (! $done) {
		   &begin();
		   &eat() if /$cookie/;
		   &run() if /$monster/;
		   &end();
	   }

The usual solution runs along the lines:

$cookie = ...;
$monster = ...;

eval "sub cookie { &eat() if /$cookie/o; }";
eval "sub monster { &run() if /$monster/o; }";

while (! $done) {
	&begin();
	&cookie;
	&monster;
	&end();
}

Now, anytime $cookie is changed, reexecute the first eval, and anytime
$monster is changed, reexecute the second eval.

If there was only one pattern searched for in the loop, you could
exploit the fact that // reuses the previous pattern.

Dale

Dale Worley		Compass, Inc.			worley@compass.com
--
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