This should do it:
typedef multi_index_container<
node,
indexed_by< hashed_unique< member<node,std::string, &node::data> >
, ordered_non_unique< member<node, int, &node::numerical> >
>
> node_type;
global_fun
expects, well, a gloabl function. &node::numerical
is a member just like &node::data
. You can of course write a function that accepts a node and extracts it, but why would you?
You are also missing the member.hpp
include.