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.. _explicit-namespaces:
Explicit namespaces in import/export
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.. extension:: ExplicitNamespaces
:shortdesc: Enable using the keyword ``type`` to specify the namespace of
entries in imports and exports (:ref:`explicit-namespaces`).
Implied by :extension:`TypeOperators` and :extension:`TypeFamilies`.
:since: 7.6.1
Enable use of explicit namespaces in module export lists.
In an import or export list, such as ::
module M( f, (++) ) where ...
import N( f, (++) )
...
the entities ``f`` and ``(++)`` are *values*. However, with type
operators (:ref:`type-operators`) it becomes possible to declare
``(++)`` as a *type constructor*. In that case, how would you export or
import it?
The :extension:`ExplicitNamespaces` extension allows you to prefix the name of
a type constructor in an import or export list with "``type``" to
disambiguate this case, thus: ::
module M( f, type (++) ) where ...
import N( f, type (++) )
...
module N( f, type (++) ) where
data family a ++ b = L a | R b
The extension :extension:`ExplicitNamespaces` is implied by
:extension:`TypeOperators` and (for some reason) by :extension:`TypeFamilies`.
In addition, with :extension:`PatternSynonyms` you can prefix the name of a
data constructor in an import or export list with the keyword
``pattern``, to allow the import or export of a data constructor without
its parent type constructor (see :ref:`patsyn-impexp`).
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