| 1 | /*! |
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| 2 | @file |
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| 3 | Forward declares `boost::hana::lift`. |
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| 4 | |
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| 5 | Copyright Louis Dionne 2013-2022 |
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| 6 | Distributed under the Boost Software License, Version 1.0. |
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| 7 | (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) |
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| 8 | */ |
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| 9 | |
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| 10 | #ifndef BOOST_HANA_FWD_LIFT_HPP |
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| 11 | #define BOOST_HANA_FWD_LIFT_HPP |
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| 12 | |
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| 13 | #include <boost/hana/config.hpp> |
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| 14 | #include <boost/hana/core/when.hpp> |
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| 15 | |
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| 16 | |
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| 17 | namespace boost { namespace hana { |
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| 18 | //! Lift a value into an `Applicative` structure. |
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| 19 | //! @ingroup group-Applicative |
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| 20 | //! |
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| 21 | //! `lift<A>` takes a normal value and embeds it into a structure whose |
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| 22 | //! shape is represented by the `A` `Applicative`. Note that the value |
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| 23 | //! may be a function, in which case the created structure may be |
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| 24 | //! `ap`plied to another `Applicative` structure containing values. |
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| 25 | //! |
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| 26 | //! |
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| 27 | //! Signature |
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| 28 | //! --------- |
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| 29 | //! Given an Applicative `A`, the signature is |
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| 30 | //! @f$ \mathtt{lift}_A : T \to A(T) @f$. |
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| 31 | //! |
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| 32 | //! @tparam A |
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| 33 | //! A tag representing the `Applicative` into which the value is lifted. |
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| 34 | //! |
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| 35 | //! @param x |
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| 36 | //! The value to lift into the applicative. |
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| 37 | //! |
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| 38 | //! |
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| 39 | //! Example |
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| 40 | //! ------- |
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| 41 | //! @include example/lift.cpp |
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| 42 | #ifdef BOOST_HANA_DOXYGEN_INVOKED |
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| 43 | template <typename A> |
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| 44 | constexpr auto lift = [](auto&& x) { |
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| 45 | return tag-dispatched; |
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| 46 | }; |
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| 47 | #else |
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| 48 | template <typename A, typename = void> |
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| 49 | struct lift_impl : lift_impl<A, when<true>> { }; |
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| 50 | |
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| 51 | template <typename A> |
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| 52 | struct lift_t { |
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| 53 | template <typename X> |
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| 54 | constexpr auto operator()(X&& x) const; |
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| 55 | }; |
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| 56 | |
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| 57 | template <typename A> |
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| 58 | BOOST_HANA_INLINE_VARIABLE constexpr lift_t<A> lift{}; |
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| 59 | #endif |
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| 60 | }} // end namespace boost::hana |
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| 61 | |
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| 62 | #endif // !BOOST_HANA_FWD_LIFT_HPP |
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| 63 | |
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