6.2.13. Lambda-case

LambdaCase

Since:

7.6.1

Status:

Included in GHC2024

Allow the use of lambda-case syntax.

The 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 allows expressions with multiple scrutinees (see GHC proposal #302) 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 LambdaCase with 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