RE: [F/O] backreferences in regexen

I'm personally sympathetic to this requirement, though with some
reservations about feature creep.

Michael Kay

> -----Original Message-----
> From: Tobias Reif [mailto:tobiasreif@pinkjuice.com] 
> Sent: 19 August 2003 09:10
> To: public-qt-comments@w3.org
> Subject: [F/O] backreferences in regexen
> 
> 
> 
> Hi
> 
> I'd like to re-raise a request I expressed in May [post1] 
> regarding the 
> addition of backreferences in regexen. It has been discussed 
> previously 
> so I expect no replies, but merely wanted it to be known that I still 
> think that XSLT 2 / XQuery 1.0 / XPath 2.0 F/O should have 
> this feature.
> 
> My research in May [langs] did show that the feature is 
> widely available 
> in programming languages and in existing regular expression 
> libraries. Among the popular languages which support 
> backreferences in regexen  are 
> Ruby, Perl, Python and Java, an ancient version of sed 
> already supported 
> this feature [sed], and the PCRE lib provides this feature 
> for C++ etc 
> so it can be used to implement regexen in many languages and apps.
> 
> F/O adds "^" and "$" to the regex set of WXS [additions] 
> which are very 
> useful, it should also add "\[number]".
> 
> Some developers (if not most) agree with me about the 
> usefulness of the 
> feature:
> 
> [mk]
> "I agree this can be a handy feature [...]"
> 
> ... and some also agree that it is very popular in addition to being 
> very useful:
> 
> [todd]
> "I agree with all of his arguments - back references are easy to 
> implement, are available in every regex library I have used over the 
> past several years, and extremely useful. Some tasks become 
> substantially more difficult without back references.
> [...]
> I believe many real-world users will be unpleasantly 
> surprised if back 
> references are not supported."
> 
> Tobi
> 
> [post1] 
> http://lists.w3.org/Archives/Public/public-qt-comments/2003May
/0288.html
(more sample output is at
http://www.pinkjuice.com/howto/vimxml/setup.xml#catalogs)

[langs]
http://lists.w3.org/Archives/Public/public-qt-comments/2003May/0298.html

[sed]
http://lists.w3.org/Archives/Public/public-qt-comments/2003May/0307.html

[additions]
http://www.w3.org/TR/xquery-operators/#regex-syntax
"The regular expression syntax and semantics for these functions are 
identical to those defined in [XML Schema Part 2: Datatypes] with the 
following additions:
[...]
Two meta-characters, ^ and $ are added. In string mode, the 
metacharacter ^ matches the start of the entire string, while $ matches 
the end of the entire string.
[...]"

[mk]
http://lists.w3.org/Archives/Public/public-qt-comments/2003May/0294.html

[todd]
http://lists.w3.org/Archives/Public/public-qt-comments/2003Jun/0125.html


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