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| author | Cyd Parser <cydparser@gmail.com> | 2017-08-06 22:23:23 -0700 |
|---|---|---|
| committer | Ben Gamari <ben@smart-cactus.org> | 2017-08-07 19:22:59 -0400 |
| commit | 14457cf6a50f708eecece8f286f08687791d51f7 (patch) | |
| tree | 621e8610872006b0c297862718a3759bd79bf0d2 | |
| parent | 2f29f198bfd04aadfae3b5a6152c855f9bb999d6 (diff) | |
| download | haskell-14457cf6a50f708eecece8f286f08687791d51f7.tar.gz | |
Fix EmptyCase documentation
| -rw-r--r-- | docs/users_guide/glasgow_exts.rst | 11 |
1 files changed, 5 insertions, 6 deletions
diff --git a/docs/users_guide/glasgow_exts.rst b/docs/users_guide/glasgow_exts.rst index d50dd40d53..bc09402668 100644 --- a/docs/users_guide/glasgow_exts.rst +++ b/docs/users_guide/glasgow_exts.rst @@ -1701,8 +1701,8 @@ example, consider these two candidate definitions of ``absurd``: :: - data a :==: b where - Refl :: a :==: a + data a :~: b where + Refl :: a :~: a absurd :: True :~: False -> a absurd x = error "absurd" -- (A) @@ -1710,10 +1710,9 @@ example, consider these two candidate definitions of ``absurd``: We much prefer (B). Why? Because GHC can figure out that ``(True :~: False)`` is an empty type. So (B) has no partiality and GHC -should be able to compile with :ghc-flag:`-Wincomplete-patterns`. (Though -the pattern match checking is not yet clever enough to do that.) On the -other hand (A) looks dangerous, and GHC doesn't check to make sure that, -in fact, the function can never get called. +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. .. _multi-way-if: |