[boost] [spirit] How to detect Spirit.Qi expressions?

Hi, Is there a way to detect at compile time that a certain type is a Boost.Spirit.Qi parser? That includes template expressions and grammars. Basically, I want to detect if qi::parse(b, e, expr) would be a sensible thing to do. I tried this: boost::is_same< typename proto::domain_of< ExpressionT >::type, spirit::qi::domain

But domain_of returns default_domain for Boost.Spirit.Qi template expressions.