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diff --git a/boost/metaparse/v1/unless_error.hpp b/boost/metaparse/v1/unless_error.hpp
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+++ b/boost/metaparse/v1/unless_error.hpp
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+#ifndef BOOST_METAPARSE_V1_UTIL_UNLESS_ERROR_HPP
+#define BOOST_METAPARSE_V1_UTIL_UNLESS_ERROR_HPP
+
+// Copyright Abel Sinkovics (abel@sinkovics.hu)  2011.
+// 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)
+
+#include <boost/metaparse/v1/is_error.hpp>
+
+#include <boost/mpl/equal_to.hpp>
+#include <boost/mpl/eval_if.hpp>
+
+namespace boost
+{
+  namespace metaparse
+  {
+    namespace v1
+    {
+      template <class T, class NotErrorCase>
+      struct unless_error :
+        boost::mpl::eval_if<typename is_error<T>::type, T, NotErrorCase>
+      {};
+    }
+  }
+}
+
+#endif
+