Re: [Boost-users] REGEXP - Serializing regexp ?

From: Eric Niebler (eric_at_[hidden])
Date: 2007-10-31 12:40:40

Jacques-Olivier Goussard wrote:
> *Eric Niebler*  wrote:
>>'ll second the suggestion to look into xpressive. With xpressive, you
>>can refer to one regex from another. And with the latest version (in the
>>Boost Sandbox) you can put your list of cities into a symbol table and
>>get very fast look-up -- much better than just a bunch of alternates.
> 
> Ok, I've taken a look and that doesn't seem to be what I need afteral.
> The regexp used must use the Perl semantic and are only known at
> runtime, so I would go for what you call dynamic expressions, however 
> I'm not sure I see
> how I can use your symbol table neat trick with those, unless they are
> disconnected. I.e. I can easily translate
> "in (CITY) on westbrook"
> into
> sregex leftre = 'in';
> sregex rightre = 'on westbrook';
> sregex re = leftre >> (city_map) >> rightre;
> 
> but what to do with
> "in (CITY|heaven) on westbrook" ?

You're right, you can't /directly/ use symbol tables in dynamic regexes, 
but you can embed a static regex into a dynamic one. See the section on 
Dynamic Regex Grammars here: http://tinyurl.com/2nacj7.

In particular, you can:

   sregex_compiler comp;
   // static regex, creates a symbol table from city_map:
   comp["CITY"] = (a1 = city_map);
   // dynamic regex calls static regex
   sregex re = comp.compile("in ((?$CITY)|heaven) on westbrook");

HTH,

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