[ANN] xpressive 0.9.3 in boost-sandbox
<< Background >> xpressive is a TR1 regex work-alike that also accepts regexes as expression templates and lets regexes nest and call each other recursively. << Significant changes since 0.9.2 >> - TR1-style regex_traits interface - Speed enhancements - syntax_option_type::ignore_white_space << Download >> xpressive.zip at: http://boost-sandbox.sf.net/vault/index.php?directory=eric_niebler << Docs >> http://boost-sandbox.sf.net/libs/xpressive -- Eric Niebler Boost Consulting www.boost-consulting.com
On Thu, Jun 30, 2005 at 12:02:18AM -0700, Eric Niebler <eric@boost-consulting.com> wrote:
<< Background >> xpressive is a TR1 regex work-alike that also accepts regexes as expression templates and lets regexes nest and call each other recursively.
How does xpressive implement recursive/nested regexes? The nested regexes look like context-free grammars. Is expressive able to handle LL-1 grammars only, or even RL grammars? Regards Andreas Pokorny PS: I have not found enough time to implement some conveniece structures for spirit scanner generation based upon xpressive :(.
Andreas Pokorny wrote:
On Thu, Jun 30, 2005 at 12:02:18AM -0700, Eric Niebler <eric@boost-consulting.com> wrote:
<< Background >> xpressive is a TR1 regex work-alike that also accepts regexes as expression templates and lets regexes nest and call each other recursively.
How does xpressive implement recursive/nested regexes? The nested regexes look like context-free grammars. Is expressive able to handle LL-1 grammars only, or even RL grammars?
Regards Andreas Pokorny
PS: I have not found enough time to implement some conveniece structures for spirit scanner generation based upon xpressive :(.
That's right, when using nested regexes with xpressive, you have the full power of context-free grammars. Its usefulness for creating parsers is limitted right now by the lack of semantic actions. Actions are a post-1.0 feature. xpressive is an exhaustive backtracking NFA, like Perl's regex. A nested regex is treated like any other matching primitive -- a tail parser. If the tail parser fails at a given point, back up and try something different. Keep trying until you succeed or until all possibilities are exhausted. It can be expensive, but there is a construct for turning off exhaustive backtracking for parts of your pattern that don't need it. -- Eric Niebler Boost Consulting www.boost-consulting.com
participants (2)
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Andreas Pokorny -
Eric Niebler