RE: Regular Expressions

["Dennis Lovelady" <iseries@xxxxxxxxxxxx>]

Thank you for your responses, John.  While I don't see the benefit of using
one individual's API under the conception that another's API is difficult to
learn/use, I salute you making this available.  I am not some other person,
and this may exactly fit that other person's needs!

But I did notice that you avoided the performance question.  I'm just
saying.  :)

Dennis Lovelady
http://www.linkedin.com/in/dennislovelady
--
"For a moment, nothing happened.  Then, after a second or so, nothing
continued to happen."
        -- The Hitchhiker's Guide to the Galaxy 


>     I had three objectives for producing this implementation.
>
>     The first objective was to use a single call instead of REGCOMP,
> REGEXEC
> and REGFREE.. This is closer to the "standard" implementation found in
> other
> languages and scripts.  It also makes regular expressions more
> accessible to
> those who are unfamiliar with the IBM api's.
>
>     My second objective was to remove the confusion / ambiguity caused
> by
> differing character sets / ccsid's.  While I cannot guarantee that my
> implementation will work successfully across all the character sets /
> ccsid's, it is more robust than the IBM-supplied api's.
>
>     My third objective was to widen the range of regular expressions
> available here.  Allied to this was the need to improve the
> documentation
> for RPG developers.
>
>     Two of the examples illustrate a return position rather than 1
> (alpha, h
> and alp25a, \d,  both of which return position 4).
>
>     Messages which can be of help in determining whether a regular
> expression is valid or not can be obtained from the return code.  A
> negative
> return code (range -1 to -18) will indicate the message based on the
> IBM
> documentation.  These return codes are in the readme, which can be
> viewed on
> line.
>
>     I agree with you in that "the hard part is in coming up with the
> right
> expression".  This is the case in all implementations of regular
> expressions.  Different implementations use different (albeit very
> similar)
> syntaxes and there is a set of standard escape characters and
> punctuation
> characters.
>
>     I had considered an implementation of REGEXEC on its own, but this
> cannot be done without a related implementation of REGCOMP.  If you
> think
> this to be useful, I will look at it again.
>
>
> Regards,
> John McKay   mba
>
> ----- Original Message -----
> From: "Dennis Lovelady" <iseries@xxxxxxxxxxxx>
> To: "'RPG programming on the IBM i / System i'" <rpg400-l@xxxxxxxxxxxx>
> Sent: Friday, August 13, 2010 10:03 AM
> Subject: RE: Regular Expressions
>
>
> > 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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> >
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