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+
+#ifndef BOOST_MPL_SEQUENCE_TAG_HPP_INCLUDED
+#define BOOST_MPL_SEQUENCE_TAG_HPP_INCLUDED
+
+// Copyright Aleksey Gurtovoy 2000-2004
+//
+// 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)
+//
+// See http://www.boost.org/libs/mpl for documentation.
+
+// $Id$
+// $Date$
+// $Revision$
+
+#include <boost/mpl/sequence_tag_fwd.hpp>
+#include <boost/mpl/aux_/has_tag.hpp>
+#include <boost/mpl/aux_/has_begin.hpp>
+#include <boost/mpl/aux_/na_spec.hpp>
+#include <boost/mpl/aux_/is_msvc_eti_arg.hpp>
+#include <boost/mpl/aux_/config/eti.hpp>
+#include <boost/mpl/aux_/yes_no.hpp>
+#include <boost/mpl/aux_/config/workaround.hpp>
+
+namespace boost { namespace mpl {
+
+// agurt, 27/nov/02: have to use a simplistic 'sequence_tag' implementation
+// on MSVC to avoid dreadful "internal structure overflow" error
+#if BOOST_WORKAROUND(BOOST_MSVC, < 1300) \
+    || defined(BOOST_MPL_CFG_NO_HAS_XXX)
+
+template<
+      typename BOOST_MPL_AUX_NA_PARAM(Sequence)
+    >
+struct sequence_tag
+{
+    typedef typename Sequence::tag type;
+};
+
+#elif BOOST_WORKAROUND(BOOST_MSVC, == 1300)
+
+// agurt, 07/feb/03: workaround for what seems to be MSVC 7.0-specific ETI issue
+
+namespace aux {
+
+template< bool >
+struct sequence_tag_impl
+{
+    template< typename Sequence > struct result_
+    {
+        typedef typename Sequence::tag type;
+    };
+};
+
+template<>
+struct sequence_tag_impl<false>
+{
+    template< typename Sequence > struct result_
+    {
+        typedef int type;
+    };
+};
+
+} // namespace aux
+
+template<
+      typename BOOST_MPL_AUX_NA_PARAM(Sequence)
+    >
+struct sequence_tag
+    : aux::sequence_tag_impl< !aux::is_msvc_eti_arg<Sequence>::value >
+        ::template result_<Sequence>
+{
+};
+
+#else
+
+namespace aux {
+
+template< bool has_tag_, bool has_begin_ >
+struct sequence_tag_impl
+{
+    // agurt 24/nov/02: MSVC 6.5 gets confused in 'sequence_tag_impl<true>' 
+    // specialization below, if we name it 'result_' here
+    template< typename Sequence > struct result2_;
+};
+
+#   define AUX_CLASS_SEQUENCE_TAG_SPEC(has_tag, has_begin, result_type) \
+template<> struct sequence_tag_impl<has_tag,has_begin> \
+{ \
+    template< typename Sequence > struct result2_ \
+    { \
+        typedef result_type type; \
+    }; \
+}; \
+/**/
+
+AUX_CLASS_SEQUENCE_TAG_SPEC(true, true, typename Sequence::tag)
+AUX_CLASS_SEQUENCE_TAG_SPEC(true, false, typename Sequence::tag)
+AUX_CLASS_SEQUENCE_TAG_SPEC(false, true, nested_begin_end_tag)
+AUX_CLASS_SEQUENCE_TAG_SPEC(false, false, non_sequence_tag)
+
+#   undef AUX_CLASS_SEQUENCE_TAG_SPEC
+
+} // namespace aux
+
+template<
+      typename BOOST_MPL_AUX_NA_PARAM(Sequence)
+    >
+struct sequence_tag
+    : aux::sequence_tag_impl<
+          ::boost::mpl::aux::has_tag<Sequence>::value
+        , ::boost::mpl::aux::has_begin<Sequence>::value
+        >::template result2_<Sequence>
+{
+};
+
+#endif // BOOST_MSVC
+
+BOOST_MPL_AUX_NA_SPEC(1, sequence_tag)
+
+}}
+
+#endif // BOOST_MPL_SEQUENCE_TAG_HPP_INCLUDED