[boost] [ANN] Xpressive 2.0.0

From: Eric Niebler (eric_at_[hidden])
Date: 2007-10-12 19:56:55

Xpressive has just reached 2.0! The new version has lots of cool new 
features (see below). Subversion and the File Vault both have the latest 
code. It works with HEAD and with Boost v1.34.1.

Below is an earlier message announcing the feature set of xpressive 2.0. 
  The latest docs are here:
http://boost-sandbox.sourceforge.net/libs/xpressive/doc/html/index.html

Also, xpressive.zip in the File Vault (Strings - Text Processing 
directory) contains the docs in pdf format.

Please grab the latest code and let me know of any problems you 
encounter so I can get them fixed for 1.35.

-- 
Eric Niebler
Boost Consulting
www.boost-consulting.com
Eric Niebler wrote:
> It's a poorly kept secret that I've been adding new features to 
> Xpressive on CVS HEAD for a while now. So here are the features already 
> implemented (documentation forthcoming) for Xpressive 2.0:
> 
> << Semantic Actions >>
> 
> Specify code to execute when parts of a regex match, a-la Spirit's 
> semantic actions. Eg.: if you want to parse a string of name/value pairs 
> into a std::map, you might:
> 
>      std::map<std::string, int> result;
>      std::string str("aaa=>1 bbb=>23 ccc=>456");
> 
>      // Like "(\\w+)=>(\\d+)":
>      sregex pair = ( (s1= +_w) >> "=>" >> (s2= +_d) )
>                    [ ref(result)[s1] = as<int>(s2) ];
>      sregex rx = pair >> *(+_s >> pair);
> 
>      if(regex_match(str, rx))
>      {
>          assert(result["aaa"] == 1);
>          assert(result["bbb"] == 23);
>          assert(result["ccc"] == 456);
>      }
> 
> The actions are placed on a queue and executed in order only when the 
> regex match succeeds.
> 
> << Custom Assertions >>
> 
> Use the check() function to create a boolean predicate that can 
> participate in the match. Here's a regex that recognizes two integers 
> only if the first is less than the second:
> 
>    sregex rx = ( (s1= +_d) >> ' ' >> (s2= +_d) )
>                [ check( as<int>(s1) < as<int>(s2) ) ];
> 
> Unlike actions, predicates execute immediately. You can also define the 
> predicate out-of-line as a function object.
> 
> << Dynamic Regex Grammars with Named Regexes >>
> 
> Using regex_compiler, you can map a name to a regex object, and then 
> refer to that regex from another by name. In this way, you can build 
> grammars from regexes at runtime.
> 
>      sregex_compiler comp;
>      sregex rx = comp.compile("^bar(?$RE)baz$");
>      comp.compile("(?$RE=)\\d+ \\d+");
> 
> There's an alternate syntax for associating a name with a regex that you 
> can use to nest a static regex in a dynamic one. Eg., the last line 
> above could be:
> 
>      comp["RE"] = +_d >> ' ' >> +_d;
> 
> With these changes, you can now nest static and dynamic regexes within 
> each other freely, giving you lots of flexibility to build grammars and 
> modify them on the fly.
> 
> << Named Captures >>
> 
> For dynamic regular expressions, you can create a named capture with 
> (?P<name> ...). You can refer back to the named capture with (?P=name). 
> In substitution strings (for use with regex_replace()), you can refer 
> back to a named capture with \\g<name> when using the format_perl or 
> format_all flags.
> 
> And more .... I'd like to give props to Dave Jenkins who has been doing 
> m4d things with this stuff already, and who has given me a laundry list 
> of other features he'd like.