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diff --git a/boost/spirit/home/x3/auxiliary/guard.hpp b/boost/spirit/home/x3/auxiliary/guard.hpp
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+++ b/boost/spirit/home/x3/auxiliary/guard.hpp
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+/*=============================================================================
+    Copyright (c) 2001-2014 Joel de Guzman
+
+    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(BOOST_SPIRIT_X3_GUARD_FERBRUARY_02_2013_0649PM)
+#define BOOST_SPIRIT_X3_GUARD_FERBRUARY_02_2013_0649PM
+
+#if defined(_MSC_VER)
+#pragma once
+#endif
+
+#include <boost/spirit/home/x3/support/context.hpp>
+#include <boost/spirit/home/x3/directive/expect.hpp>
+
+namespace boost { namespace spirit { namespace x3
+{
+    enum class error_handler_result
+    {
+        fail
+      , retry
+      , accept
+      , rethrow
+    };
+
+    template <typename Subject, typename Handler>
+    struct guard : unary_parser<Subject, guard<Subject, Handler>>
+    {
+        typedef unary_parser<Subject, guard<Subject, Handler>> base_type;
+        static bool const is_pass_through_unary = true;
+
+        guard(Subject const& subject, Handler handler)
+          : base_type(subject), handler(handler) {}
+
+        template <typename Iterator, typename Context
+          , typename RuleContext, typename Attribute>
+        bool parse(Iterator& first, Iterator const& last
+          , Context const& context, RuleContext& rcontext, Attribute& attr) const
+        {
+            for (;;)
+            {
+                try
+                {
+                    Iterator i = first;
+                    bool r = this->subject.parse(i, last, context, rcontext, attr);
+                    if (r)
+                        first = i;
+                    return r;
+                }
+                catch (expectation_failure<Iterator> const& x)
+                {
+                    switch (handler(first, last, x, context))
+                    {
+                        case error_handler_result::fail:
+                            return false;
+                        case error_handler_result::retry:
+                            continue;
+                        case error_handler_result::accept:
+                            return true;
+                        case error_handler_result::rethrow:
+                            throw;
+                    }
+                }
+            }
+            return false;
+        }
+
+        Handler handler;
+    };
+}}}
+
+#endif