Prologue and Epilogue
=====================

Every source in |hysj| starts by including the prologue, and ends by including the epilogue. These introduce and unintroduce some unhygenic, but ergonomic, macros. The macros are cleaned up in the epilogue. 

*Example*

.. code-block:: cpp
   
   #include<yada.hpp>

   #include<hysj/detail/prologue.hpp>
   namespace hysj::inline _HYSJ_VERSION_NAMESPACE::something{
     //yada yada.
   }
   #include<hysj/detail/epilogue.hpp>

Prologue
--------
:cpp:include:`#include<hysj/detail/prologue.hpp>`

.. c:macro:: fwd(expression)

   Simpler :cppref:`std::forward <utility/forward>`.

   |

.. c:macro:: arrow(sequence)
	     
   Expects a sequence of :cpp:expr:`(expression)(constraint)`, where :cpp:expr:`constraint` is optional.
			  
   Sets up noexcept-specification, trailing return type deduction, and a function body, repating :cpp:expr:`expression` 3 times. If :cpp:expr:`constraint` is supplied it will be pasted as a return-type-requirement on :cpp:expr:`expression`.

   *Example*

   Defines a function:
	     
   .. code-block:: cpp

      constexpr add_one(auto x)
        arrow((x + 1)(-> std::integral))

   equivalent to:

   .. code-block:: cpp

      constexpr add_one(auto x) noexcept(noexcept(x+1))
        -> decltype(auto)
        requires requires { { x + 1 } -> std::integral; }
      { return x + 1; }

   |

.. c:macro:: lift(identifier)
             
   Lifts :cpp:expr:`identifier` into a variadic lambda using :c:macro:`arrow`.

   *Example*

   Invokes a range of callables:

   .. code-block:: cpp

      std::ranges::for_each(callables,lift(std::invoke));

   |

.. c:macro:: reify(expression)
             
   Extracts the nested type-alias :cpp:expr:`type` from the uncvref'd type of the expression.

   *Example*

   Computes type from :cppref:`identity_type <types/identity_type>` expression:

   .. code-block:: cpp

      static_assert(std::is_same_v<reify(std::identity_type<int>{}),int>);

   |
			     
Epilogue
--------

:cpp:include:`#include<hysj/detail/epilogue.hpp>`

Undefines the unhygenic, non-namespace-prefixed, macros introduced in the prologue_.