[x3d-public] X3D Regex

Wed Jun 6 17:31:48 PDT 2018

On Wed, Jun 6, 2018 at 7:38 PM, Joseph D Williams <joedwil at earthlink.net>
wrote:

>
>
> *From: *Andreas Plesch <andreasplesch at gmail.com>
> *Sent: *Wednesday, June 6, 2018 4:05 PM
> *To: *Joseph D Williams <joedwil at earthlink.net>
> *Cc: *X3D Graphics public mailing list <x3d-public at web3d.org>
> *Subject: *Re: [x3d-public] X3D Regex
>
>
>
> On Wed, Jun 6, 2018 at 4:51 PM, Joseph D Williams <joedwil at earthlink.net>
> wrote:
>
> HI,
>
>
>
>
>
> *From: *Andreas Plesch <andreasplesch at gmail.com>
> *Sent: *Wednesday, June 6, 2018 10:39 AM
> *To: *X3D Graphics public mailing list <x3d-public at web3d.org>
> *Subject: *Re: [x3d-public] X3D Regex
>
>
>
> > Date: Wed, 6 Jun 2018 09:23:09 -0700
>
> > From: Don Brutzman <brutzman at nps.edu>
>
> > To: X3D Graphics Working Group <x3d at web3d.org>
>
> > Cc: X3D Graphics public mailing list <x3d-public at web3d.org>, "Humanoid
>
> >         Animation (H-Anim) Working Group" <h-anim at web3d.org>
>
> > Subject: [x3d-public] X3D teleconference 5 JUN 2018 minutes: HAnim
>
> >         DIS, X3D Regex, Web3D 2018 and X3Dv4
>
> >
>
> ...
>
> >         X3D Regular Expressions (regexes)
>
> >         http://www.web3d.org/specifications/X3dRegularExpressions.html
>
> >
>
> > Vince reports that MFInt32 problem stack-overflow error still remains
> when running X3D Schematron locally.  He will post the abridged example
> that is still failing, hopefully that will help our test efforts.
>
> >
>
> > MFInt32 regex pattern:
>
> >
>
> >         ((\+|\-)?(0|[1-9][0-9]*)?( )?(,)?( )?)*
>
> >         http://www.web3d.org/specifications/X3dRegularExpressions.html#
> MFInt32
>
>
>
> >> I am looking at this regex and have a few questions.
>
>
>
> >> All groups are optional, so it seems to also match an empty string "".
>
> >> Perhaps not a problem, or even intentional.
>
>
>
> Totally intentional. We need the ability to legally load the node with no
> content then later, prior to actually running the scene. Add some attr
> content.
>
>
>
> >>> Yes, so the question is really if an empty string is a legal value. It
> may be intended as a signal to use the default value.
>
>
>
> Fine observation. The default value may be the empty string.
>

>
> >> It matches a mix of commas and spaces, for example ",,,  , ,, ,,  ".
>
> That is an error. Look at the entire range of X3DFields. I don’t think we
> want to allow a comma inside a tuple, just blank or comma between fields.
>
> >> This does not look like an acceptable MFInt32 value.
>
>
>
> Well, either space or comma is legal sep. Mix reads poorly but legal if
> number of
>
>
>
> Not sure if there are no digits and just commas and spaces. "1,,2,,3" also
> matches. but I doubt that skipping entries is legal.
>
>
>
> Matches what,
>

The regex in question here: ((\+|\-)?(0|[1-9][0-9]*)?( )?(,)?( )?)*

> there is a long list of X3DFOe;d forms and X3DArrayFIeld forms. Pretty
> sure that “,,” has got to be an error. However, look at implementations and
> see that most can be flexible to give the copy/paste or hand coder a break
> and at least not kill. .
>

Yes, better be generous rather than too strict.

>
>
> >> The second group (0|[1-9][0-9]*) : This is harder to understand. It
>
> seems to want to address leading zeros. Why not just use ([0-9]*) ?
>
> Using https://regexr.com/ and https://regex101.com/ I could not come
>
> up with a pattern where these expressions were not equivalent. What
>
> would be an example where ([0-9]*) would not work ?
>
>
>
> leading zero for decimal value?
>
>
>
> >>> [0-9]* matches 012 as well, so still looking for an example.
>
>
>
> 012 is the same as 12 so maybe intent is leading 0 in decimals
>

Yes, but leading 0 do not require the full (0|[1-9][0-9]*)
expression.Simply [0-9]* suffices.

> There are fields where a 0 is legal. Again, I think there is a regex for
> every X3D field and X3DArrayField type,
>

I think we are still looking for a regex for SFImage.

>
>
> >> http://www.web3d.org/documents/specifications/19776-1/V3.3/Part01/
> EncodingOfFields.html#SFInt32
>
> allows hexadecimal values, using 0x prefix. I have never seen this but
>
> the regex would not match, eg. produces a false negative.
>
>
>
> Looks like hex needs better regex.
>
>
>
>
>
> Tempted to give it a try, starting with SFInt32:
>
> /[ \t]*[-|+]?((0x([0-9]|[a-f]|[A-F])+)|[0-9]*)[ \t]*/
>
>
>
> Translation: optional whitespace followed by optional plus or minus signs
> followed by
>
> either 0x followed by a at least one digit or a to f or A to F letter
>
> or by zero or more digits
>
> followed by white space.
>
>
>
> Is tab legal white space ? Is whitespace after the plus/minus sign allowed
> ? Hm, I guess so.
>
>
>
> >>> Testing this regex shows it works pretty well. One issue that it
> matches "  +  " without any digits. One could require at least one digit
> but then the empty string does not match any more. So one could make the
> complete  regex optional:
>
>
>
> >>> /([ \t]*[-|+]?[ \t]*((0x([0-9]|[a-f]|[A-F])+)|[0-9]+)[ \t]*)?/
>
>
>
> So, for this one, the correct answer is Either this regex or the empty
> string. Seems like we ought to be able to say that. Esp for MFs where the
> [] is signal for empty
>

That the idea. To accommodate "" as empty array [].

>
>
> >>> How does that look for SFInt32 ? There is \d for digits and \s for
> white space but I am not sure how widely supported these are.
>
> >>> /(\s*[-|+]?\s*((0x(\d|[a-f]|[A-F])+)|\d+)\s*)?/
>
>
>
> Has any toolmaker shown their regex? I don’t know what is the spec for
> ww3regex.
>

I do not think w3 deals with regexes directly. Javascript does and has \s
and \d classes.

Given the SFInt32 regex. for MFInt32 it ought to possible to say : this
regex followed by an optional comma, all matched at least 0 times:
/(\s*[-|+]?\s*((0x(\d|[a-f]|[A-F])+)|\d+)\s*,?)*/

Testing looks good ! Let me nominate above a better regex for MFInt32,

-Andreas

Best, Andreas

> >> -Andreas
>
>
>
> Thanks and Best,
>
> Joe
>
>
>
> This mail thing I have gets lost in the processing very easy
>
>
>
> --
>
> Andreas Plesch
>
> Waltham, MA 02453
>
>
>
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>
>
>
>
>
> --
>
> Andreas Plesch
> Waltham, MA 02453
>
>
>

-- 
Andreas Plesch
Waltham, MA 02453
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