I had to write an invoke metafunction because I couldn't seem to find one that looked like it was what I needed:
template < typename MF > struct invoke { typedef typename MF::type type; };
I've looked through the documentation TOC: http://www.boost.org/doc/libs/1_42_0/libs/mpl/doc/refmanual/refmanual_toc.html
Is there something I'm missing?