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+/*!
+@file
+Forward declares `boost::hana::append`.
+
+@copyright Louis Dionne 2013-2016
+Distributed under the Boost Software License, Version 1.0.
+(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
+ */
+
+#ifndef BOOST_HANA_FWD_APPEND_HPP
+#define BOOST_HANA_FWD_APPEND_HPP
+
+#include <boost/hana/config.hpp>
+#include <boost/hana/core/when.hpp>
+
+
+BOOST_HANA_NAMESPACE_BEGIN
+    //! Append an element to a monadic structure.
+    //! @ingroup group-MonadPlus
+    //!
+    //! Given an element `x` and a monadic structure `xs`, `append` returns a
+    //! new monadic structure which is the result of lifting `x` into the
+    //! monadic structure and then combining that (to the right) with `xs`.
+    //! In other words,
+    //! @code
+    //!     append(xs, x) == concat(xs, lift<Xs>(x))
+    //! @endcode
+    //! where `Xs` is the tag of `xs`. For sequences, this has the intuitive
+    //! behavior of simply appending an element to the end of the sequence,
+    //! hence the name.
+    //!
+    //! > #### Rationale for not calling this `push_back`
+    //! > See the rationale for using `prepend` instead of `push_front`.
+    //!
+    //!
+    //! Signature
+    //! ---------
+    //! Given a MonadPlus `M`, the signature is
+    //! @f$ \mathtt{append} : M(T) \times T \to M(T) @f$.
+    //!
+    //! @param xs
+    //! A monadic structure that will be combined to the left of the element.
+    //!
+    //! @param x
+    //! An element to combine to the right of the monadic structure.
+    //!
+    //!
+    //! Example
+    //! -------
+    //! @include example/append.cpp
+#ifdef BOOST_HANA_DOXYGEN_INVOKED
+    constexpr auto append = [](auto&& xs, auto&& x) {
+        return tag-dispatched;
+    };
+#else
+    template <typename M, typename = void>
+    struct append_impl : append_impl<M, when<true>> { };
+
+    struct append_t {
+        template <typename Xs, typename X>
+        constexpr auto operator()(Xs&& xs, X&& x) const;
+    };
+
+    constexpr append_t append{};
+#endif
+BOOST_HANA_NAMESPACE_END
+
+#endif // !BOOST_HANA_FWD_APPEND_HPP