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| author | Jakob Bruenker <jakob.bruenker@gmail.com> | 2022-03-21 00:14:25 +0100 |
|---|---|---|
| committer | Jakob Bruenker <jakob.bruenker@gmail.com> | 2022-03-31 17:45:37 +0200 |
| commit | a9c0c69b42657d39f26ab822241900ba0f308dc3 (patch) | |
| tree | fd59a5e49146ee436e04137b313d8e4178c2bed0 /docs/users_guide/exts/lambda_case.rst | |
| parent | dda46e2da13268c239db3290720b014cef00c01d (diff) | |
| download | haskell-wip/T20768.tar.gz | |
Implement \cases (Proposal 302)wip/T20768
This commit implements proposal 302: \cases - Multi-way lambda
expressions.
This adds a new expression heralded by \cases, which works exactly like
\case, but can match multiple apats instead of a single pat.
Updates submodule haddock to support the ITlcases token.
Closes #20768
Diffstat (limited to 'docs/users_guide/exts/lambda_case.rst')
| -rw-r--r-- | docs/users_guide/exts/lambda_case.rst | 19 |
1 files changed, 16 insertions, 3 deletions
diff --git a/docs/users_guide/exts/lambda_case.rst b/docs/users_guide/exts/lambda_case.rst index 74bc84e164..6872101698 100644 --- a/docs/users_guide/exts/lambda_case.rst +++ b/docs/users_guide/exts/lambda_case.rst @@ -18,7 +18,20 @@ which is equivalent to :: \freshName -> case freshName of { p1 -> e1; ...; pN -> eN } -Note that ``\case`` starts a layout, so you can write :: +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 @@ -26,8 +39,8 @@ Note that ``\case`` starts a layout, so you can write :: pN -> eN Additionally, since GHC 9.0.1, combining :extension:`LambdaCase` with -:extension:`Arrows` allows ``\case`` syntax to be used as a command in -``proc`` notation: :: +: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 |