6.3.4. Explicit namespaces in import/export¶
- ExplicitNamespaces¶
- Implied by:
- 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 (Type operators) it becomes possible to declare
(++) as a type constructor. In that case, how would you export or
import it?
The 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 ExplicitNamespaces is implied by
TypeOperators and (for some reason) by TypeFamilies.
In addition, with 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 Import and export of pattern synonyms).