Editing Persistent data structure (section)

=== Haskell ===
Haskell is a [[pure functional language]] and therefore does not allow for mutation. Therefore, all data structures in the language are persistent, as it is impossible to not preserve the previous state of a data structure with functional semantics.<ref>{{Cite web|url=https://www.haskell.org/|title=Haskell Language|website=www.haskell.org|access-date=2018-10-22}}</ref> This is because any change to a data structure that would render previous versions of a data structure invalid would violate [[referential transparency]].

In its standard library Haskell has efficient persistent implementations for linked lists,<ref>{{Cite web|url=http://hackage.haskell.org/package/base-4.12.0.0/docs/Data-List.html|title=Data.List|website=hackage.haskell.org|access-date=2018-10-23}}</ref> Maps (implemented as size balanced trees),<ref>{{Cite web|url=http://hackage.haskell.org/package/containers-0.6.0.1/docs/Data-Map-Strict.html|title=Data.Map.Strict|website=hackage.haskell.org|access-date=2018-10-23}}</ref> and Sets<ref>{{Cite web|url=http://hackage.haskell.org/package/containers-0.6.0.1/docs/Data-Set.html|title=Data.Set|website=hackage.haskell.org|access-date=2018-10-23}}</ref> among others.<ref>{{Cite web|url=https://wiki.haskell.org/Performance/Arrays|title=Performance/Arrays - HaskellWiki|website=wiki.haskell.org|language=en|access-date=2018-10-23}}</ref>