stabilize build system: depends, installer, boost/bdb fixes, cross targets groundwork

depends/x86_64-pc-linux-gnu/include/boost/hana/fwd/prepend.hpp

@@ -0,0 +1,73 @@
+/*!
+@file
+Forward declares `boost::hana::prepend`.
+
+@copyright Louis Dionne 2013-2017
+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_PREPEND_HPP
+#define BOOST_HANA_FWD_PREPEND_HPP
+
+#include <boost/hana/config.hpp>
+#include <boost/hana/core/when.hpp>
+
+
+BOOST_HANA_NAMESPACE_BEGIN
+    //! Prepend an element to a monadic structure.
+    //! @ingroup group-MonadPlus
+    //!
+    //! Given a monadic structure `xs` and an element `x`, `prepend` returns
+    //! a new monadic structure which is the result of lifting `x` into the
+    //! monadic structure and then combining that (to the left) with `xs`.
+    //! In other words,
+    //! @code
+    //!     prepend(xs, x) == concat(lift<Xs>(x), xs)
+    //! @endcode
+    //!
+    //! For sequences, this has the intuitive behavior of simply prepending
+    //! an element to the beginning of the sequence, hence the name.
+    //!
+    //! > #### Rationale for not calling this `push_front`
+    //! > While `push_front` is the de-facto name used in the standard library,
+    //! > it also strongly suggests mutation of the underlying sequence, which
+    //! > is not the case here. The author also finds that `push_front`
+    //! > suggests too strongly the sole interpretation of putting an
+    //! > element to the front of a sequence, whereas `prepend` is slightly
+    //! > more nuanced and bears its name better for e.g. `hana::optional`.
+    //!
+    //!
+    //! Signature
+    //! ---------
+    //! Given a MonadPlus `M`, the signature is
+    //! @f$ \mathtt{prepend} : M(T) \times T \to M(T) @f$.
+    //!
+    //! @param xs
+    //! A monadic structure that will be combined to the right of the element.
+    //!
+    //! @param x
+    //! An element to combine to the left of the monadic structure.
+    //!
+    //!
+    //! Example
+    //! -------
+    //! @include example/prepend.cpp
+#ifdef BOOST_HANA_DOXYGEN_INVOKED
+    constexpr auto prepend = [](auto&& xs, auto&& x) {
+        return tag-dispatched;
+    };
+#else
+    template <typename M, typename = void>
+    struct prepend_impl : prepend_impl<M, when<true>> { };
+
+    struct prepend_t {
+        template <typename Xs, typename X>
+        constexpr auto operator()(Xs&& xs, X&& x) const;
+    };
+
+    constexpr prepend_t prepend{};
+#endif
+BOOST_HANA_NAMESPACE_END
+
+#endif // !BOOST_HANA_FWD_PREPEND_HPP