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.. _lambda-case:
Lambda-case
-----------
.. extension:: LambdaCase
:shortdesc: Enable lambda-case expressions.
:since: 7.6.1
Allow the use of lambda-case syntax.
The :extension:`LambdaCase` extension enables expressions of the form ::
\case { p1 -> e1; ...; pN -> eN }
which is equivalent to ::
\freshName -> case freshName of { p1 -> e1; ...; pN -> eN }
Since GHC 9.4.1, it also allow expressions with multiple scrutinees (see GHC
proposal `#302 <https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0302-cases.rst>`_)
of the form ::
\cases { p11 ... pM1 -> e1; ...; p1N ... pMN -> eN }
which is equivalent to a function defined as ::
f p11 ... pM1 = e1
...
f p1N ... pMN = eN
Note that both ``\case`` and ``\cases`` start a layout, so you can write ::
\case
p1 -> e1
...
pN -> eN
Additionally, since GHC 9.0.1, combining :extension:`LambdaCase` with
:extension:`Arrows` allows ``\case`` (and since GHC 9.4.1 ``\cases``)
syntax to be used as a command in ``proc`` notation: ::
proc x -> (f -< x) `catchA` \case
p1 -> cmd1
...
pN -> cmdN
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