boost/xpressive/detail/static/transforms/as_alternate.hpp
///////////////////////////////////////////////////////////////////////////////
// as_alternate.hpp
//
// Copyright 2007 Eric Niebler. 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)
#ifndef BOOST_XPRESSIVE_DETAIL_STATIC_TRANSFORMS_AS_ALTERNATE_HPP_EAN_04_01_2007
#define BOOST_XPRESSIVE_DETAIL_STATIC_TRANSFORMS_AS_ALTERNATE_HPP_EAN_04_01_2007
// MS compatible compilers support #pragma once
#if defined(_MSC_VER) && (_MSC_VER >= 1020)
# pragma once
#endif
#include <boost/config.hpp>
#include <boost/mpl/assert.hpp>
#include <boost/type_traits/is_same.hpp>
#include <boost/xpressive/proto/traits.hpp>
#include <boost/xpressive/proto/matches.hpp>
#include <boost/xpressive/proto/transform/fold.hpp>
#include <boost/xpressive/proto/transform/branch.hpp>
#include <boost/xpressive/proto/transform/fold_tree.hpp>
#include <boost/xpressive/detail/detail_fwd.hpp>
#include <boost/xpressive/detail/static/static.hpp>
#include <boost/xpressive/detail/core/matcher/alternate_matcher.hpp>
#include <boost/xpressive/detail/utility/cons.hpp>
namespace boost { namespace xpressive { namespace detail
{
///////////////////////////////////////////////////////////////////////////////
// alternates_list
// a fusion-compatible sequence of alternate expressions, that also keeps
// track of the list's width and purity.
template<typename Head, typename Tail>
struct alternates_list
: fusion::cons<Head, Tail>
{
BOOST_STATIC_CONSTANT(std::size_t, width = Head::width == Tail::width ? Head::width : unknown_width::value);
BOOST_STATIC_CONSTANT(bool, pure = Head::pure && Tail::pure);
alternates_list(Head const &head, Tail const &tail)
: fusion::cons<Head, Tail>(head, tail)
{
}
};
template<typename Head>
struct alternates_list<Head, fusion::nil>
: fusion::cons<Head, fusion::nil>
{
BOOST_STATIC_CONSTANT(std::size_t, width = Head::width);
BOOST_STATIC_CONSTANT(bool, pure = Head::pure);
alternates_list(Head const &head, fusion::nil const &tail)
: fusion::cons<Head, fusion::nil>(head, tail)
{
}
};
///////////////////////////////////////////////////////////////////////////////
// in_alternate
template<typename Grammar>
struct in_alternate
: Grammar
{
in_alternate();
template<typename Expr, typename State, typename Visitor>
struct apply
{
typedef alternates_list<
typename Grammar::template apply<Expr, alternate_end_xpression, Visitor>::type
, State
> type;
};
template<typename Expr, typename State, typename Visitor>
static typename apply<Expr, State, Visitor>::type
call(Expr const &expr, State const &state, Visitor &visitor)
{
return typename apply<Expr, State, Visitor>::type(
Grammar::call(expr, alternate_end_xpression(), visitor)
, state
);
}
};
///////////////////////////////////////////////////////////////////////////////
// as_alternate_matcher
template<typename Grammar>
struct as_alternate_matcher
: Grammar
{
as_alternate_matcher();
template<typename Expr, typename State, typename Visitor>
struct apply
{
typedef alternate_matcher<
typename Grammar::template apply<Expr, State, Visitor>::type
, typename Visitor::traits_type
> type;
};
template<typename Expr, typename State, typename Visitor>
static typename apply<Expr, State, Visitor>::type
call(Expr const &expr, State const &state, Visitor &visitor)
{
return typename apply<Expr, State, Visitor>::type(
Grammar::call(expr, state, visitor)
);
}
};
///////////////////////////////////////////////////////////////////////////////
// as_alternate
template<typename Grammar>
struct as_alternate
: as_alternate_matcher<
proto::transform::reverse_fold_tree<
typename Grammar::proto_tag
, in_alternate<typename Grammar::proto_arg0>
, fusion::nil
>
>
{
BOOST_MPL_ASSERT((
is_same<
typename Grammar::proto_arg0
, typename Grammar::proto_arg1
>
));
};
}}}
#endif