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Diffstat (limited to 'docs')
| -rw-r--r-- | docs/users_guide/safe_haskell.rst | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/docs/users_guide/safe_haskell.rst b/docs/users_guide/safe_haskell.rst index 3914820ebe..6ce8b8fc26 100644 --- a/docs/users_guide/safe_haskell.rst +++ b/docs/users_guide/safe_haskell.rst @@ -278,6 +278,15 @@ Furthermore, we restrict the following features: between types. Derived instances (through the :ghc-flag:`-XDeriveDataTypeable` extension) are still allowed. +- ``GHC.Generics`` — Hand crafted instances of the ``Generic`` type class are + not allowed in Safe Haskell. Such instances aren't strictly unsafe, but + there is an important invariant that a ``Generic`` instance should adhere to + the structure of the data type for which the instance is defined, and + allowing manually implemented ``Generic`` instances would break that + invariant. Derived instances (through the :ghc-flag:`-XDeriveGeneric` + extension) are still allowed. Refer to the + :ref:`generic programming <generic-programming>` section for more details. + .. _safe-overlapping-instances: Safe Overlapping Instances |