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diff --git a/docs/users_guide/exts/deriving.rst b/docs/users_guide/exts/deriving.rst new file mode 100644 index 0000000000..d10260b21f --- /dev/null +++ b/docs/users_guide/exts/deriving.rst @@ -0,0 +1,41 @@ +.. _deriving: + +Deriving mechanism +================== + +Haskell 98 allows the programmer to add a deriving clause to a data type +declaration, to generate a standard instance declaration for specified class. +GHC extends this mechanism along several axes: + +* The derivation mechanism can be used separately from the data type + declaration, using the :ref:`standalone deriving mechanism + <stand-alone-deriving>`. + +* In Haskell 98, the only derivable classes are ``Eq``, + ``Ord``, ``Enum``, ``Ix``, ``Bounded``, ``Read``, and ``Show``. :ref:`Various + language extensions <deriving-extra>` extend this list. + +* Besides the stock approach to deriving instances by generating all method + definitions, GHC supports two additional deriving strategies, which can + derive arbitrary classes: + + * :ref:`Generalised newtype deriving <newtype-deriving>` for newtypes and + * :ref:`deriving any class <derive-any-class>` using an empty instance + declaration. + + The user can optionally declare the desired :ref:`deriving strategy + <deriving-strategies>`, especially if the compiler chooses the wrong + one :ref:`by default <default-deriving-strategy>`. + + +.. toctree:: + :maxdepth: 1 + + empty_data_deriving + deriving_inferred + standalone_deriving + deriving_extra + newtype_deriving + derive_any_class + deriving_strategies + deriving_via |