Boost C++ Libraries

boost/spirit/home/qi/operator/alternative.hpp

/*=============================================================================
    Copyright (c) 2001-2011 Joel de Guzman
    Copyright (c) 2001-2011 Hartmut Kaiser

    Distributed under the Boost Software License, Version 1.0. (See accompanying
    file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
=============================================================================*/
#if !defined(SPIRIT_ALTERNATIVE_FEBRUARY_05_2007_1153AM)
#define SPIRIT_ALTERNATIVE_FEBRUARY_05_2007_1153AM

#if defined(_MSC_VER)
#pragma once
#endif

#include <boost/spirit/home/qi/detail/alternative_function.hpp>
#include <boost/spirit/home/qi/meta_compiler.hpp>
#include <boost/spirit/home/qi/parser.hpp>
#include <boost/spirit/home/qi/detail/attributes.hpp>
#include <boost/spirit/home/support/has_semantic_action.hpp>
#include <boost/spirit/home/support/handles_container.hpp>
#include <boost/spirit/home/support/detail/what_function.hpp>
#include <boost/spirit/home/support/unused.hpp>
#include <boost/spirit/home/support/info.hpp>
#include <boost/fusion/include/any.hpp>
#include <boost/fusion/include/mpl.hpp>
#include <boost/fusion/include/for_each.hpp>

namespace boost { namespace spirit
{
    ///////////////////////////////////////////////////////////////////////////
    // Enablers
    ///////////////////////////////////////////////////////////////////////////
    template <>
    struct use_operator<qi::domain, proto::tag::bitwise_or> // enables |
      : mpl::true_ {};

    template <>
    struct flatten_tree<qi::domain, proto::tag::bitwise_or> // flattens |
      : mpl::true_ {};
}}

namespace boost { namespace spirit { namespace qi
{
    template <typename Elements>
    struct alternative : nary_parser<alternative<Elements> >
    {
        template <typename Context, typename Iterator>
        struct attribute
        {
            // Put all the element attributes in a tuple
            typedef typename traits::build_attribute_sequence<
                Elements, Context, traits::alternative_attribute_transform
              , Iterator, qi::domain
            >::type all_attributes;

            // Ok, now make a variant over the attribute sequence. Note that
            // build_variant makes sure that 1) all attributes in the variant
            // are unique 2) puts the unused attribute, if there is any, to
            // the front and 3) collapses single element variants, variant<T>
            // to T.
            typedef typename
                traits::build_variant<all_attributes>::type
            type;
        };

        alternative(Elements const& elements_)
          : elements(elements_) {}

        template <typename Iterator, typename Context
          , typename Skipper, typename Attribute>
        bool parse(Iterator& first, Iterator const& last
          , Context& context, Skipper const& skipper
          , Attribute& attr_) const
        {
            detail::alternative_function<Iterator, Context, Skipper, Attribute>
                f(first, last, context, skipper, attr_);

            // return true if *any* of the parsers succeed
            return fusion::any(elements, f);
        }

        template <typename Context>
        info what(Context& context) const
        {
            info result("alternative");
            fusion::for_each(elements,
                spirit::detail::what_function<Context>(result, context));
            return result;
        }

        Elements elements;
    };

    ///////////////////////////////////////////////////////////////////////////
    // Parser generators: make_xxx function (objects)
    ///////////////////////////////////////////////////////////////////////////
    template <typename Elements, typename Modifiers>
    struct make_composite<proto::tag::bitwise_or, Elements, Modifiers>
      : make_nary_composite<Elements, alternative>
    {};
}}}

namespace boost { namespace spirit { namespace traits
{
    ///////////////////////////////////////////////////////////////////////////
    template <typename Elements>
    struct has_semantic_action<qi::alternative<Elements> >
      : nary_has_semantic_action<Elements> {};

    ///////////////////////////////////////////////////////////////////////////
    template <typename Elements, typename Attribute, typename Context
      , typename Iterator>
    struct handles_container<qi::alternative<Elements>, Attribute, Context
      , Iterator>
      : nary_handles_container<Elements, Attribute, Context, Iterator> {};
}}}

#endif