I'm a little confused on the correct way to lazily call a boost::function
in a phoenix expression. For example, this doesn't do anything:

namespace bp = boost::phoenix;
namespace bpa = bp::arg_names;

struct Foo
{
   boost::function< void() > callback;

   Foo(boost::function< void() > const& callback) :
      callback(callback)
   {
   }
};

main()
{
   std::list< Foo > foos;

   foos.push_back(Foo(std::cout << bp::val(1) << '\n'));
   foos.push_back(Foo(std::cout << bp::val(2) << '\n'));
   foos.push_back(Foo(std::cout << bp::val(3) << '\n'));

   std::for_each(
      foos.begin(),
      foos.end(),
     bp::bind(&Foo::callback, bpa::arg1));
}

If I wrap the bind(...) in another bind(...) it'll work, but is that the
right way? I'm not binding anything, I just want the callback called.