recursive_test.cpp

#include "boost/variant.hpp"

#include <iostream>
#include <sstream>
#include <vector>
#include <boost/cstdlib.hpp>

struct vector_printer
    : boost::static_visitor<std::string>
{
    template <typename T>
    auto operator()(const std::vector<T>& vec) const -> std::string 
    {
        std::ostringstream ost;

        ost << "( ";

        typename std::vector<T>::const_iterator it = vec.begin();
        for (; it != vec.end(); ++it)
            ost << boost::apply_visitor(vector_printer(), *it);

        ost << ") ";

        return ost.str();
    }

    template <typename T>
    auto operator()(const T& operand) const -> std::string
    {
        std::ostringstream ost;
        ost << operand << ' ';
        return ost.str();
    }
};

int main(int , char* [])
{
  typedef boost::make_recursive_variant<
    int, 
    std::vector<boost::recursive_variant_>
  >::type var_t;

  std::vector<var_t> vec;
  vec.push_back(3);
  vec.push_back(5);
  vec.push_back(vec);
  vec.push_back(7);

  var_t var(vec);
  std::string result( boost::apply_visitor( vector_printer(), var ) );

  std::cout << "result: " << result << '\n';
  // BOOST_CHECK(result == "( 3 5 ( 3 5 ) 7 ) ");

  return boost::exit_success;
}