Example on how to do asynchronous http get request using cpp-netlib

I'm trying to do asynchronous http requests using cpp-netlib. I couldn't find any examples of this in the documentation, as a result can't even get it to compile. My current attempt is below (with compilation errors in the comments). Any hints how to make it work? Thank you in advance!

#include <iostream>
#include <boost/network/protocol/http/client.hpp>

using namespace std;
using namespace boost::network;
using namespace boost::network::http;

typedef function<void(boost::iterator_range<char const *> const &, boost::system::error_code const &)> body_callback_function_type; // ERROR: Expected initializer before '<' token

body_callback_function_type callback() // ERROR: 'body_callback_function_type' does not name a type
{
    cout << "This is my callback" << endl;
}

int main() {
    http::client client;
    http::client::request request("http://www.google.com/");
    http::client::response response = client.get(request, http::_body_handler=callback()); // ERROR: 'callback' was not declared in this scope
    cout << body(response) << endl;
    return 0;
}