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| -rw-r--r-- | docs/users_guide/exts/control.rst | 8 |
1 files changed, 7 insertions, 1 deletions
diff --git a/docs/users_guide/exts/control.rst b/docs/users_guide/exts/control.rst index a94def72b5..84c2aa1208 100644 --- a/docs/users_guide/exts/control.rst +++ b/docs/users_guide/exts/control.rst @@ -18,7 +18,7 @@ Language extensions can be controlled (i.e. allowed or not) in two ways: ``{-# LANGUAGE TemplateHaskell #-}`` (see :ref:`language-pragma`). .. extension:: GHC2021 - :shortdesc: Use GHC’s set of default languages from 2021 + :shortdesc: Use GHC’s set of default language extensions from 2021 GHC blesses a number of extensions, beyond Haskell 2010, to be suitable to turned on by default. These extensions are considered to be stable and @@ -29,6 +29,12 @@ Language extensions can be controlled (i.e. allowed or not) in two ways: ``GHC20xx`` by default, users are advised to declare the language set explicitly with ``-XGHC2021``. + Note that, because GHC2021 includes a number of non-standardized + extensions, the stability guarantees it provides are not quite as strong as + those provided by, e.g., :extension:`Haskell2010`. While GHC does take + pains to avoid changing the semantics of these extensions, changes may + still happen (e.g. the simplified subsumption change introduced in GHC 9.0 + which caused GHC to reject some programs using :extension:`RankNTypes`). The ``GHC2021`` language set comprises the following extensions: |