The definition of Fusion polymorphic function object will be changed shortly to be consistent with boost.resultof. Instead of requiring a nested result metafunction of the form: template<typename T0, typename T1, ... typename TN> struct result { typedef xxx type; }; A polymorphic function object will instead simply be required to suppport boost::result_of<F(A,B,...Z)>::type as a valid expression. This will break some Fusion client code, specifically, if you are using fold, accumulate, transform, or a lot of the components in the functional section of the library, you may need to make changes to support this change. The change should be entered into CVS head over the forthcoming weekend. Apologies to anyone whos code this breaks, but this should make things more consistent with the rest of boost going forwards. Cheers Dan ___________________________________________________________ Yahoo! Mail is the world's favourite email. Don't settle for less, sign up for your free account today http://uk.rd.yahoo.com/evt=44106/*http://uk.docs.yahoo.com/mail/winter07.htm...