Re: [boost] [xpressive]: nested regular expressions for dynamic xpressive and basic_regex assignment

From: Eric Niebler (eric_at_[hidden])
Date: 2007-08-27 16:23:16

Andreas Pokorny wrote:
> Hi Eric,
> 
> Eric Niebler wrote:
>> (Sorry for the delay, I just got back from a week-long vacation.)
>>
>> Andreas Pokorny wrote:
>>> Do you see a nicer solution?
>> Hi Andreas. I *also* recently made nested regexes work for dynamic
>> regexes, and I made an announcement about it on this list not too long
>> ago. See here: http://lists.boost.org/Archives/boost/2007/06/122641.php.
> 
> Oh dear, I switched from my old gmx email account to the gmail based for
> boost, there are still 7k unread boost messages.

I guess you've got some reading to do. ;-)

>> In particular, see "Dynamic Regex Grammars with Named Regexes", which
>> has the following example:
>>
>>     sregex_compiler comp;
>>     sregex rx = comp.compile("^bar(?$RE)baz$");
>>     comp.compile("(?$RE=)\\d+ \\d+");
>>
>> The regex_compiler holds a map from names to regex objects. The first
>> call to compile() creates a forward reference to a regex object named
>> "RE" and the second call binds a regex to the name "RE".
>>
>> Is this the sort of thing you had in mind? (This is only available in
>> the repository -- no public release has this feature yet.)
> 
> (?$ looks like an assertion. I wanted to use that feature to implement
> configureable/extensible syntax highlighting withing quickbook. What
> happens if you add RE regex line
> e.g. comp.compile("(?$RE=)\\w+ ");

You mean add that line after the other two? It should replace the 
meaning of (?$RE) in all the regexes that refer to $RE. The syntax is 
something I made up and is evocative of a Perl variable assignment.

> Did you consider a different syntax for specifiying named regular
> expressions, or is (?$=) and (?$) something that exists in other regex engine?

I made that syntax up and I'm not attached to it. I don't know of any 
prior art in this area, except that design work for Perl 6. I don't 
recall not what they're using or why I didn't go with it. :-P Can you 
suggest a better syntax?

-- 
Eric Niebler
Boost Consulting
www.boost-consulting.com
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