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diff --git a/boost/hana/tap.hpp b/boost/hana/tap.hpp
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+/*!
+@file
+Defines `boost::hana::tap`.
+
+@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_TAP_HPP
+#define BOOST_HANA_TAP_HPP
+
+#include <boost/hana/fwd/tap.hpp>
+
+#include <boost/hana/concept/monad.hpp>
+#include <boost/hana/config.hpp>
+#include <boost/hana/core/dispatch.hpp>
+#include <boost/hana/functional/partial.hpp>
+#include <boost/hana/lift.hpp>
+
+
+BOOST_HANA_NAMESPACE_BEGIN
+    template <typename M>
+    struct tap_t {
+    #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
+        static_assert(hana::Monad<M>::value,
+        "hana::tap<M> requires 'M' to be a Monad");
+    #endif
+
+        template <typename F>
+        constexpr auto operator()(F&& f) const {
+            using Tap = BOOST_HANA_DISPATCH_IF(tap_impl<M>,
+                hana::Monad<M>::value
+            );
+
+            return Tap::apply(static_cast<F&&>(f));
+        }
+    };
+
+    namespace detail {
+        template <typename M>
+        struct tap_helper {
+            template <typename F, typename X>
+            constexpr auto operator()(F&& f, X&& x) const {
+                (void)static_cast<F&&>(f)(x);
+                return hana::lift<M>(static_cast<X&&>(x));
+            }
+        };
+    }
+
+    template <typename M, bool condition>
+    struct tap_impl<M, when<condition>> : default_ {
+        template <typename F>
+        static constexpr auto apply(F&& f)
+        { return hana::partial(detail::tap_helper<M>{}, static_cast<F&&>(f)); }
+    };
+BOOST_HANA_NAMESPACE_END
+
+#endif // !BOOST_HANA_TAP_HPP