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Re: [netmod] regular expression flavours (again)

"Rob Wilton (rwilton)" <rwilton@cisco.com> Fri, 14 June 2019 10:08 UTC

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From: "Rob Wilton (rwilton)" <rwilton@cisco.com>
To: Carsten Bormann <cabo@tzi.org>
CC: Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de>, Robert Varga <nite@hq.sk>, NETMOD WG <netmod@ietf.org>
Thread-Topic: [netmod] regular expression flavours (again)
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Date: Fri, 14 Jun 2019 10:08:36 +0000
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Subject: Re: [netmod] regular expression flavours (again)
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> -----Original Message-----
> From: Carsten Bormann <cabo@tzi.org>
> Sent: 14 June 2019 10:57
> To: Rob Wilton (rwilton) <rwilton@cisco.com>
> Cc: Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de>; Robert
> Varga <nite@hq.sk>; NETMOD WG <netmod@ietf.org>
> Subject: Re: [netmod] regular expression flavours (again)
> 
> On Jun 14, 2019, at 11:29, Rob Wilton (rwilton) <rwilton@cisco.com> wrote:
> >
> > I'm sure that someone can post an XKCD of why this is a bad idea 😉
> 
> Yeah, going ahead and standardizing another regex dialect that is subtly
> incompatible with everything else is exactly what we need.

This is not what I am suggesting.

We don't need a standard regex dialect that is subtly incompatible with all the normal regex implementations because that is exactly what W3C produced.

What I am suggesting is standardizing a regex dialect that is well defined and widely compatible with normal regex engines.  I.e. a standardized subset of PCRE.

> 
> We could even make sure that dialect is actually useful in a pattern
> statement (e.g., by making it self-anchoring).

I don't think that adding/removing the anchor characters is really the issue, since they are trivial to add/remove as required.


> 
> But wait, somebody has already done that work for us!
> 
> W3C did, when they designed their XSD-types… So we are done already!

I disagree, please see above.


> 
> Now the main deployability problem with W3C XSD regexes is that they added
> some functionality that is sorely missing in other dialects, such as
> character class subtraction, so it is more than an hour of work to write a
> converter from XSD regexes to you favorite flavor.  Maybe we should
> encourage some open source software in this space…

Or perhaps we could define a regex language that worked with normal implementations without requiring any conversion.

Thanks,
Rob


> 
> Grüße, Carsten
> 
>

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