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.. _overloaded-record-dot:
Overloaded record dot
---------------------
.. extension:: OverloadedRecordDot
:shortdesc: Record '.' syntax
:since: 9.2.0
Provides record '.' syntax e.g. ``x.foo``
When ``OverloadedRecordDot`` is enabled one can write ``a.b`` to mean the ``b`` field of the ``a`` record expression.
Example:
.. code-block:: haskell
{-# LANGUAGE OverloadedRecordDot #-}
{-# LANGUAGE DuplicateRecordFields #-}
data Person = Person { name :: String }
data Company = Company { name :: String, owner :: Person }
main = do
let c = Company { name = "Acme Corp."
, owner = Person { name = "Wile E. Coyote" } }
print $ c.name ++ " is run by " ++ c.owner.name
You may also write ``(.b)`` to mean a function that "projects the ``b`` field from its argument". For example, ``(.b) a`` means the same thing as ``a.b``).
``OverloadedRecordDot`` is normally implemented by desugaring record ``.`` expressions to ``GHC.Records.getField`` expressions. By enabling ``OverloadedRecordDot`` and ``RebindableSyntax`` together it is possible to desugar ``.`` expressions into your own ``getField`` implementations.
When considering ``a.b``, the ``b`` field that is meant is determined by solving ``HasField`` constraints. See :ref:`solving-hasfield-constraints`.
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