[boost] Phoenix: is there a Phoenix expression trait?

Subject: [boost] Phoenix: is there a Phoenix expression trait?
From: Vicente BOTET (vicente.botet_at_[hidden])
Date: 2011-05-14 14:18:22

Hi,

I'm adding a convert_to Phoenix like functor to Boost.Conversion.

I would like to use the same name, i.e. convert_to, but the overloads conflict. I would like to use sfinae to choose the correct overloading between

template 
inline
typename expression::convert_to, U>::type const
convert_to(U const& u);

template 
Target convert_to(Source const& from, boost::dummy::base_tag const& p=boost::dummy::base_tag())

Is there a trait that can be used to detect if the parameter is a Phoenix expression?

BTW, I have just based my implementation on the one for static_cast, that uses the detail 
boost::phoenix::detail::target

Could someone explain me why this is needed?
Could this detail be moved to the user interface?

Best,
Vicente