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Diffstat (limited to 'docs/users_guide/exts/empty_case.rst')
| -rw-r--r-- | docs/users_guide/exts/empty_case.rst | 5 |
1 files changed, 3 insertions, 2 deletions
diff --git a/docs/users_guide/exts/empty_case.rst b/docs/users_guide/exts/empty_case.rst index c42de22e9e..7a32f609e6 100644 --- a/docs/users_guide/exts/empty_case.rst +++ b/docs/users_guide/exts/empty_case.rst @@ -19,6 +19,9 @@ or :: \case { } -- -XLambdaCase is also required +Note that it is not allowed for ``\cases``, since it would be unclear how many +patterns are being matched. + This can be useful when you know that the expression being scrutinised has no non-bottom values. For example: @@ -45,5 +48,3 @@ We much prefer (B). Why? Because GHC can figure out that is able to compile with :ghc-flag:`-Wincomplete-patterns` and :ghc-flag:`-Werror`. On the other hand (A) looks dangerous, and GHC doesn't check to make sure that, in fact, the function can never get called. - - |