Chris@16: /*==============================================================================
Chris@16:     Copyright (c) 2005-2010 Joel de Guzman
Chris@16: 
Chris@16:     Distributed under the Boost Software License, Version 1.0. (See accompanying
Chris@16:     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
Chris@16: ==============================================================================*/
Chris@16: #ifndef BOOST_PHOENIX_CORE_NOTHING_HPP
Chris@16: #define BOOST_PHOENIX_CORE_NOTHING_HPP
Chris@16: 
Chris@16: #include <boost/phoenix/core/limits.hpp>
Chris@16: #include <boost/mpl/void.hpp>
Chris@16: #include <boost/phoenix/core/actor.hpp>
Chris@16: #include <boost/phoenix/core/call.hpp>
Chris@16: #include <boost/phoenix/core/expression.hpp>
Chris@16: #include <boost/phoenix/core/value.hpp>
Chris@16: 
Chris@16: namespace boost { namespace phoenix
Chris@16: {
Chris@16:     /////////////////////////////////////////////////////////////////////////////
Chris@16:     //
Chris@16:     //  null_actor
Chris@16:     //
Chris@16:     //      An actor that does nothing (a "bum", if you will :-).
Chris@16:     //
Chris@16:     /////////////////////////////////////////////////////////////////////////////
Chris@16:     
Chris@16:     namespace detail
Chris@16:     {
Chris@16:         struct nothing {};
Chris@16:     }
Chris@16:     
Chris@16:     namespace expression
Chris@16:     {
Chris@16:         struct null
Chris@16:             : expression::value<detail::nothing>
Chris@16:         {};
Chris@16:     }
Chris@16:     
Chris@16:     template<typename Dummy>
Chris@16:     struct is_custom_terminal<detail::nothing, Dummy>
Chris@16:       : mpl::true_
Chris@16:     {};
Chris@16: 
Chris@16:     template<typename Dummy>
Chris@16:     struct custom_terminal<detail::nothing, Dummy>
Chris@16:     {
Chris@16:         typedef void result_type;
Chris@16:         template <typename Context>
Chris@16:         void operator()(detail::nothing, Context &) const
Chris@16:         {
Chris@16:         }
Chris@16:     };
Chris@16: 
Chris@16:     typedef expression::null::type nothing_type;
Chris@16: #ifndef BOOST_PHOENIX_NO_PREDEFINED_TERMINALS
Chris@16:     nothing_type const nothing = {{{}}};
Chris@16: #endif
Chris@16: }}
Chris@16: 
Chris@16: #endif