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.. _monadfail-desugaring:
New monadic failure desugaring mechanism
----------------------------------------
.. extension:: MonadFailDesugaring
:shortdesc: Enable monadfail desugaring.
:since: 8.0.1
Use the ``MonadFail.fail`` instead of the legacy ``Monad.fail`` function
when desugaring refutable patterns in ``do`` blocks.
The ``-XMonadFailDesugaring`` extension switches the desugaring of
``do``-blocks to use ``MonadFail.fail`` instead of ``Monad.fail``.
This extension is enabled by default since GHC 8.6.1, under the
`MonadFail Proposal (MFP)
<https://gitlab.haskell.org/haskell/prime/-/wikis/libraries/proposals/monad-fail>`__.
This extension is temporary, and will be deprecated in a future release.
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