#include <boost/variant.hpp>
#include <boost/tuple/tuple.hpp>

#include <vector>

namespace boost
{
//The following code is modelled after that shown here:
//
//  http://www.boost.org/doc/libs/1_43_0/doc/html/variant/tutorial.html#variant.tutorial.recursive
//
//IOW:
//
//   expression in tutorial corresponds to maybe_tree here.
//   binary_op<X> in tutorial corresponds to tuple_tree here.
//
//
struct null_tree{};
struct tuple_tree
;
    typedef
  variant
  < null_tree
  , recursive_wrapper
    < tuple_tree
    >
  >
maybe_tree
;  
struct tuple_tree
: tuple
  < int
  , std::vector<maybe_tree>
  >
{
};

}//exit boost namespace
  
using namespace boost;

#include <iostream>

int main(void)
{
    maybe_tree mt;
    std::cout<<"&maybe_tree="<<static_cast<void*>(&mt)<<"\n";
    null_tree& nt=get<null_tree>(mt);
    mt = tuple_tree();
    tuple_tree& tt=get<tuple_tree>(mt);
    std::cout<<"&null_tree="<<static_cast<void*>(&nt)<<"\n";
    std::cout<<"&tuple_tree="<<static_cast<void*>(&tt)<<"\n";
    //the following should throw a 'boost::bad_get' exception:
    null_tree& et=get<null_tree>(mt);
    std::cout<<"&err_tree="<<static_cast<void*>(&et)<<"\n";
    return 0;
}