Re: Regular Expressions

Rory,

The optional operator for running REGFREE each time is a good one. Thanks.

Let me think about it and see how best to implement that. Also I want to wait before I do any changes to monitor feedback.


Regards,
John McKay mba


----- Original Message ----- From: "Rory Hewitt" <rory.hewitt@xxxxxxxxx>
To: "RPG programming on the IBM i / System i" <rpg400-l@xxxxxxxxxxxx>
Sent: Friday, August 13, 2010 5:15 PM
Subject: Re: Regular Expressions

John,

I like the look of it, but I have a couple of 'concerns'.

1. Could you implement it so that you don't need to explicitly pass the
terminating null character? Easy to check within your REGEXP procedure, and
means that RPG programmers won't have to mess around themselves.

2. Following on from Dennis's concern(s), could you pass an (optional) final
parameter to say wheter you want to perform REGFREE? Then, REGEXP can check
whetherthe regexp has changed since the last time (and perform REGCOMP if
necessary), and only do REGFREE if specified (or when the ActGrp ends, of
course):


H bnddir('QC2LE')

D intotest s 256
D inpattern s 256

d regexp pr 10i 0 extproc('regexp')
d xtotest * value options(*string)
d xpattern * value options(*string)
d regfree 10i 0 options(*nopass)

d xreturn s 10i 0
d totest s like(intotest)
d totestptr s * inz(%addr(totest))
d pattern s like(inpattern)
d patternptr s * inz(%addr(pattern))

d cnull c x'00'
d REGFREE c 0


/free

intotest = 'myname@xxxxxxxxxxxxxxxx';
inpattern = '\w+@\w+\.\w{2,3}$';

totest = %trim(intotest);
pattern = %trim(inpattern);

xreturn = regexp (totestptr: patternptr: REGFREE);

dsply xreturn;

*inlr = *on;

/end-free


Just a thought (or two)

Rory

p.s. I still really like it. Don't think that these are all negatives - just
observations...

On Fri, Aug 13, 2010 at 3:56 AM, John McKay <jmckay@xxxxxxxxxxxxxxxx> wrote:

Hi Dennis,

Thanks for your comments.

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

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