[boost] [xpressive] capture float?

Hi all, I'm trying to capture a float with xpressive and put it into a local map. As a simplified example, I tried just pushing the matched pattern to a float and the result is always a float containing '0'. namespace xpr = boost::xpressive; std::map l_floatOperMap; xpr::sregex l_relation = xpr::as_xpr("<=") | ">=" | "<" | ">"); l_floatRestriction = !(xpr::s1 = l_relation) >> (xpr::s2 = (+xpr::_d >> '.' >> +xpr::_d)) [xpr::ref(l_floatOperMap)[xpr::as<float>(xpr::s2)] = xpr::asstd::string(xpr::s1)]; However, when I go to print the contents of l_floatOperMap, it contains only the tuple (0, ""). Is it something I'm doing wrong? It seems like this should work to me. Thanks, Greg