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Diffstat (limited to 'docs/users_guide/9.4.1-notes.rst')
| -rw-r--r-- | docs/users_guide/9.4.1-notes.rst | 21 |
1 files changed, 18 insertions, 3 deletions
diff --git a/docs/users_guide/9.4.1-notes.rst b/docs/users_guide/9.4.1-notes.rst index a2cced7294..caac4e9362 100644 --- a/docs/users_guide/9.4.1-notes.rst +++ b/docs/users_guide/9.4.1-notes.rst @@ -22,9 +22,24 @@ Language If you want to retain the old behavior, add a (backward-compatible) type signature, explicitly requesting this unusual quantification. -- GHC no longer checks for ``-XGADTs`` or ``-XTypeFamilies`` in order to use - an equality constraint in a type. This is part of accepted proposal - `#371 <https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0371-non-magical-eq.md>`_. +- GHC Proposal `#371 <https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0371-non-magical-eq.md>`_ has been implemented. This means: + + * The use of equality constraints no longer requires ``-XGADTs`` or ``-XTypeFamilies``. + + * The use of equality constraint syntax ``a ~ b`` requires ``-XTypeOperators``, + otherwise results in a warning (:ghc-flag:`-Wtype-equality-requires-operators`). + + * ``(~)`` is now a legal name for a user-defined type operator: + :: + + class a ~ b where + ... + + This used to be rejected with "Illegal binding of built-in syntax". + + * The built-in type equality is now exported from ``Data.Type.Equality`` and + re-exported from ``Prelude``. When ``(~)`` is not in scope, its use results + in a warning (:ghc-flag:`-Wtype-equality-out-of-scope`). - There were previously cases around functional dependencies and injective type families where the result of type inference would depend on the order |