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diff --git a/boost/hana/while.hpp b/boost/hana/while.hpp
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+/*!
+@file
+Defines `boost::hana::while_`.
+
+@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_WHILE_HPP
+#define BOOST_HANA_WHILE_HPP
+
+#include <boost/hana/fwd/while.hpp>
+
+#include <boost/hana/bool.hpp>
+#include <boost/hana/concept/constant.hpp>
+#include <boost/hana/concept/constant.hpp>
+#include <boost/hana/concept/logical.hpp>
+#include <boost/hana/config.hpp>
+#include <boost/hana/core/to.hpp>
+#include <boost/hana/core/dispatch.hpp>
+#include <boost/hana/detail/canonical_constant.hpp>
+
+#include <type_traits>
+
+
+BOOST_HANA_NAMESPACE_BEGIN
+    //! @cond
+    template <typename Pred, typename State, typename F>
+    constexpr decltype(auto) while_t::operator()(Pred&& pred, State&& state, F&& f) const {
+        using Cond = decltype(pred(state));
+        using Bool = typename hana::tag_of<Cond>::type;
+        using While = BOOST_HANA_DISPATCH_IF(while_impl<Bool>,
+            hana::Logical<Bool>::value
+        );
+
+    #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
+        static_assert(hana::Logical<Bool>::value,
+        "hana::while_(pred, state, f) requires 'pred(state)' to be a Logical");
+    #endif
+
+        return While::apply(static_cast<Pred&&>(pred),
+                            static_cast<State&&>(state),
+                            static_cast<F&&>(f));
+    }
+    //! @endcond
+
+    template <typename L, bool condition>
+    struct while_impl<L, hana::when<condition>> : hana::default_ {
+        template <typename ...Args>
+        static constexpr auto apply(Args&& ...) = delete;
+    };
+
+    template <typename L>
+    struct while_impl<L, hana::when<std::is_arithmetic<L>::value>> {
+        template <typename Pred, typename State, typename F>
+        static auto apply(Pred&& pred, State&& state, F&& f)
+            -> decltype(
+                true ? f(static_cast<State&&>(state))
+                     : static_cast<State&&>(state)
+            )
+        {
+            if (pred(state)) {
+                decltype(auto) r = f(static_cast<State&&>(state));
+                return hana::while_(static_cast<Pred&&>(pred),
+                                    static_cast<decltype(r)&&>(r),
+                                    static_cast<F&&>(f));
+            }
+            else {
+                return static_cast<State&&>(state);
+            }
+        }
+    };
+
+    template <typename C>
+    struct while_impl<C, hana::when<
+        hana::Constant<C>::value &&
+        hana::Logical<typename C::value_type>::value
+    >> {
+        template <typename Pred, typename State, typename F>
+        static constexpr State
+        while_helper(hana::false_, Pred&&, State&& state, F&&) {
+            return static_cast<State&&>(state);
+        }
+
+        template <typename Pred, typename State, typename F>
+        static constexpr decltype(auto)
+        while_helper(hana::true_, Pred&& pred, State&& state, F&& f) {
+            decltype(auto) r = f(static_cast<State&&>(state));
+            return hana::while_(static_cast<Pred&&>(pred),
+                                static_cast<decltype(r)&&>(r),
+                                static_cast<F&&>(f));
+        }
+
+        template <typename Pred, typename State, typename F>
+        static constexpr decltype(auto)
+        apply(Pred&& pred, State&& state, F&& f) {
+            // Since `pred(state)` returns a `Constant`, we do not actually
+            // need to call it; we only need its decltype. However, we still
+            // call it to run potential side effects. I'm not sure whether
+            // that is desirable, since we pretty much take for granted that
+            // functions are pure, but we'll do it like this for now. Also, I
+            // think there is something rather deep hidden behind this, and
+            // understanding what must be done here should give us a better
+            // understanding of something non-trivial.
+            auto cond_ = pred(state);
+            constexpr auto cond = hana::value(cond_);
+            constexpr bool truth_value = hana::if_(cond, true, false);
+            return while_helper(hana::bool_c<truth_value>,
+                                static_cast<Pred&&>(pred),
+                                static_cast<State&&>(state),
+                                static_cast<F&&>(f));
+        }
+    };
+BOOST_HANA_NAMESPACE_END
+
+#endif // !BOOST_HANA_WHILE_HPP