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| author | David Feuer <david.feuer@gmail.com> | 2017-02-07 00:16:55 -0500 |
|---|---|---|
| committer | David Feuer <David.Feuer@gmail.com> | 2017-02-07 00:16:56 -0500 |
| commit | 2219c8cd612ec7920a3bd1661b3c663575737267 (patch) | |
| tree | 43c944b3fd09c9719a27f871abba1a6ece01e16b /docs/users_guide | |
| parent | a28a55211d6fb8d3182b0a9e47656ff9ca8a3766 (diff) | |
| download | haskell-2219c8cd612ec7920a3bd1661b3c663575737267.tar.gz | |
Derive <$
Using the default definition of `<$` for derived `Functor`
instance is very bad for recursive data types. Derive
the definition instead.
Fixes #13218
Reviewers: austin, bgamari, RyanGlScott
Reviewed By: RyanGlScott
Subscribers: RyanGlScott, thomie
Differential Revision: https://phabricator.haskell.org/D3072
Diffstat (limited to 'docs/users_guide')
| -rw-r--r-- | docs/users_guide/8.2.1-notes.rst | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/docs/users_guide/8.2.1-notes.rst b/docs/users_guide/8.2.1-notes.rst index 36ed2b90d8..a01ad1a9d5 100644 --- a/docs/users_guide/8.2.1-notes.rst +++ b/docs/users_guide/8.2.1-notes.rst @@ -138,6 +138,11 @@ Compiler -- uses of `Monoid MyMonoid` here are improved bar :: MonadWriter MyMonoid m => ... +- GHC now derives the definition of ``<$`` when using ``DeriveFunctor`` + rather than using the default definition. This prevents unnecessary + allocation and a potential space leak when deriving ``Functor`` for + a recursive type. + GHCi ~~~~ |