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| -rw-r--r-- | docs/users_guide/8.0.2-notes.rst | 13 |
1 files changed, 13 insertions, 0 deletions
diff --git a/docs/users_guide/8.0.2-notes.rst b/docs/users_guide/8.0.2-notes.rst index 9bc78ea224..fa7aa8db3d 100644 --- a/docs/users_guide/8.0.2-notes.rst +++ b/docs/users_guide/8.0.2-notes.rst @@ -86,6 +86,19 @@ Language instance {-# OVERLAPPING #-} Foo Int +- GHC now adheres more closely to the Haskell 2010 Report with respect to + defaulting rules. As a result, GHC will now reject some defaulting rules + which GHC 8.0.1 and earlier would accept. For example, this is now + rejected :: + + module Foo where + default (Bool) + + because when the :ghc-flag:`-XExtendedDefaultRules` extension is not + enabled, defaulting rules only work for the ``Num`` class, of which ``Bool`` + is not an instance. To make GHC accept the above program, simply enable the + :ghc-flag:`-XExtendedDefaultRules` extension. + Compiler ~~~~~~~~ |