(Currently I'm on vacation. Sorry for the delay.) Jorge Lodos Vigil wrote:
Hi We are using xpressive with a grammar to match certain patterns. In some cases, we have the need to ignore white spaces. Using dynamic regexes, this can be achieved with the ignore_white_space constant. Is there a way to ignore white spaces using a grammar in xpressive other than modifying the grammar itself? We know spirit is an option, but we need to evaluate parsing speed with as many methods as possible. Thanks in advance.
I see that Dave has offered a couple of creative solutions, but that they interact badly with backtracking. What we really need is a whitespace skipping directive. Neither dynamic nor static xpressive has one. (The ignore_white_space option is like perl's /x option, and certainly doesn't do what you want.) The only thing I can think of off the top of my head is to do something like the following: BOOST_PROTO_AUTO( _ws, keep(*_w) ); ... and then use _ws in your grammar wherever you want to ignore whitespace, like: sregex rx = "some stuff" >> _ws >> "other stuff"; _ws will efficiently eat up the whitespace. Not ideal, but it works. If you don't want to use BOOST_PROTO_AUTO, the following is equivalent: boost::proto::unary_expr< boost::xpressive::detail::keeper_tag , boost::proto::dereference< boost::proto::terminal< boost::xpressive::detail::posix_charset_placeholder >::type >::type
::type const _ws = {{{{"w", false}}}};
-- Eric Niebler Boost Consulting www.boost-consulting.com