docs/users_guide/9.4.1-notes.rst


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.. _release-9-4-1:

Version 9.4.1
==============

``base`` library
~~~~~~~~~~~~~~~~

- ``GHC.Exts.magicDict`` now has the type: ::

        magicDict :: forall {rr :: RuntimeRep} dt st (r :: TYPE rr). (dt => r) -> st -> r

  ``magicDict`` can now be used without defining an intermediate data type. For
  example, the ``withTypeable`` function from the ``Data.Typeable`` module can
  now be defined as: ::

        withTypeable :: forall k (a :: k) rep (r :: TYPE rep). ()
                     => TypeRep a -> (Typeable a => r) -> r
        withTypeable rep k = magicDict @(Typeable a) k rep

  Note that the explicit type application is required, as the call to
  ``magicDict`` would be ambiguous otherwise.