RE: Regular Expressions

Yes, the approach I tend to use, is to cache up to 10 expressions. And it
could be implemented into a utility procedure, with the caveat that one
would have to (rather, "should") remember to free associated space at end of
program. This important step may not be so easy for the developer to
remember, and no error will result if it's forgotten. In some designs, it's
very difficult even to accomplish.

I cannot see what's happening under the covers (wish I could - it'd be fun
to see how another might do it), so all I could do was raise questions. You
note I had no problem with that challenge. ;)

Dennis Lovelady
http://www.linkedin.com/in/dennislovelady
--
No time spent with a cat on your lap, can ever be considered 'wasted.'

-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx [mailto:rpg400-l-
bounces@xxxxxxxxxxxx] On Behalf Of Charles Wilt
Sent: Friday, August 13, 2010 8:54 AM
To: RPG programming on the IBM i / System i
Subject: Re: Regular Expressions

Dennis,

It would seem to me that your concerns could be simply addressed by
keeping track of the last expression REGCOMP'd and not doing the
REGFREE until the expression changes or the activation group ends.

In fact, if it we're me, I'd consider keeping a lookup table of
expressions and either the DS or pointers to dynamically allocated DSs
that REGCOMP uses.

That way you could have more than one regex "active" as it were.

Charles

On Fri, Aug 13, 2010 at 5:03 AM, Dennis Lovelady <iseries@xxxxxxxxxxxx>
wrote:

Thanks, John.  I've seen implementations like this before (but not

public

domain).  I cannot download and restore a save file to the systems I

access,

so there is conjecture here.  That conjecture can be solved by having

a FAQ

for the product.  I presume that you're doing REGCOMP, REGEXP,

REGFREE with

each operation.  Have you measured the performance of this against

the

alternative (REGCOMP at the beginning of a process, REGEXP for each

of x

million rows/columns/whatevers, REGFREE at the end?

My studies on this (which I unfortunately cannot share) suggest that

one

would be much better off using REGCOMP and REGFREE themselves, rather

than

taking such a generic approach.  After all, the hard part isn't in

calling

those expressions or evaluating their results; the hard part is in

coming up

with the right expression, and that remains a hurdle with your

approach.

In other words, what is the value-add that may be traded for

performance?

Your examples, when they find a match, find them in position 1, and

return a

1.  What happens if a match is found in position n?

When one makes a mistake with a regular expression, what help

(optional or

otherwise) does the function return?

Dennis Lovelady
http://www.linkedin.com/in/dennislovelady
--
"Better to remain silent and be thought a fool than to speak out and

remove

all doubt."
       -- Abraham Lincoln

Single function regular expressions  - regexp - now available for

free

at www.rpglanguage.com/regexp

Regards,
John McKay  mba
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