[Boost-users] [Proto] How to access the grammar of an expression?

Hi, ist there a way to access the grammar that was used to construct an expression? I have defined a metafunction template struct grammar_less: mpl::false_ {}; which has specialization for some grammar combinations. Now I want to define a function that can take two arguments so that child0.grammar < child1.grammar Any idea how to do that? My test-code is attached. Regards, Roland