Editing Functional programming (section)

=== Functional programming in non-functional languages ===

It is possible to use a functional style of programming in languages that are not traditionally considered functional languages.<ref>{{cite journal |last=Hartel |first=Pieter |author2=Henk Muller |author3=Hugh Glaser |title=The Functional C experience |journal=Journal of Functional Programming |volume=14 |issue=2 |pages=129–135 |date=March 2004 |url=http://www.ub.utwente.nl/webdocs/ctit/1/00000084.pdf |doi=10.1017/S0956796803004817 |s2cid=32346900 |accessdate=2006-05-28 |archivedate=2011-07-19 |archiveurl=https://web.archive.org/web/20110719201553/http://www.ub.utwente.nl/webdocs/ctit/1/00000084.pdf |url-status=deviated }}; {{cite web |title=Functional programming in Python, Part 3 |url=http://www-128.ibm.com/developerworks/linux/library/l-prog3.html |archive-url=https://web.archive.org/web/20071016124848/http://www-128.ibm.com/developerworks/linux/library/l-prog3.html |archive-date=2007-10-16 |author=David Mertz |access-date=2006-09-17 |work=IBM developerWorks }}([https://web.archive.org/web/20071016124848/http://www-128.ibm.com/developerworks/linux/library/l-prog.html Part 1], [https://web.archive.org/web/20071016124848/http://www-128.ibm.com/developerworks/linux/library/l-prog2.html Part 2])</ref> For example, both [[D (programming language)|D]]<ref>{{cite web |url=http://www.digitalmars.com/d/2.0/function.html#pure-functions |title=Functions&nbsp;— D Programming Language 2.0 |publisher=Digital Mars |date=30 December 2012}}</ref> and [[Fortran 95]]<ref name=fortran95/> explicitly support pure functions.

[[JavaScript]], [[Lua (programming language)|Lua]],<ref>{{cite web|url=http://www.luafaq.org/#T1.2|title=Lua Unofficial FAQ (uFAQ)}}</ref> [[Python (programming language)|Python]] and [[Go (programming language)|Go]]<ref>{{Cite web|title=First-Class Functions in Go - The Go Programming Language|url=https://golang.org/doc/codewalk/functions/|access-date=2021-01-04|website=golang.org}}</ref> had [[First-class function|first class functions]] from their inception.<ref>{{cite web|url=https://brendaneich.com/2008/04/popularity/|first=Brendan|last= Eich|title=Popularity|date=3 April 2008}}</ref> Python had support for "[[anonymous function|lambda]]", "[[Map (higher-order function)|map]]", "[[Fold (higher-order function)|reduce]]", and "[[Filter (higher-order function)|filter]]" in 1994, as well as closures in Python 2.2,<ref>{{cite web |url=http://python-history.blogspot.de/2009/04/origins-of-pythons-functional-features.html |title=Origins of Python's "Functional" Features |last=van Rossum |first=Guido |author-link=Guido van Rossum |date=2009-04-21 |access-date=2012-09-27}}</ref> though Python 3 relegated  "reduce" to the <code>functools</code> standard library module.<ref>{{cite web |url=https://docs.python.org/dev/library/functools.html#functools.reduce |title=functools — Higher order functions and operations on callable objects |publisher=Python Software Foundation |date=2011-07-31 |access-date=2011-07-31}}</ref> First-class functions have been introduced into other mainstream languages such as [[Perl]] 5.0 in 1994, [[PHP]] 5.3, [[Visual Basic 9]], [[C Sharp (programming language)|C#]] 3.0, [[C++11]], and [[Kotlin (programming language)|Kotlin]].<ref name=":0"/>{{citation needed|date=April 2015}}

In Perl, [[anonymous function|lambda]], [[Map (higher-order function)|map]], [[Fold (higher-order function)|reduce]], [[Filter (higher-order function)|filter]], and [[Closure (computer science)|closures]] are fully supported and frequently used.  The book [[Higher-Order Perl]], released in 2005, was written to provide an expansive guide on using Perl for functional programming.

In PHP, [[anonymous class]]es, [[Closure (computer science)|closures]] and lambdas are fully supported. Libraries and language extensions for immutable data structures are being developed to aid programming in the functional style.

In [[Java (programming language)|Java]], anonymous classes can sometimes be used to simulate closures;<ref>{{cite book |last=Skarsaune |first=Martin |title=The SICS Java Port Project Automatic Translation of a Large Object Oriented System from Smalltalk to Java |year=2008}}</ref> however, anonymous classes are not always proper replacements to closures because they have more limited capabilities.<ref>{{cite web|last=Gosling|first=James|title=Closures|url= http://blogs.oracle.com/jag/entry/closures|work=James Gosling: on the Java Road|publisher=Oracle|access-date=11 May 2013|archive-url= https://web.archive.org/web/20130414180002/https://blogs.oracle.com/jag/entry/closures|archive-date=2013-04-14|url-status=dead}}</ref> Java 8 supports lambda expressions as a replacement for some anonymous classes.<ref>{{cite web|url=https://blogs.oracle.com/javatraining/entry/java_se_8_lambda_quick|title=Java SE 8 Lambda Quick Start|first=Michael|last=Williams|date=8 April 2013}}</ref>

In [[C Sharp (programming language)|C#]], anonymous classes are not necessary, because closures and lambdas are fully supported. Libraries and language extensions for immutable data structures are being developed to aid programming in the functional style in C#.

Many [[object-oriented]] [[Design pattern (computer science)|design patterns]] are expressible in functional programming terms: for example, the [[strategy pattern]] simply dictates use of a higher-order function, and the [[visitor (design pattern)|visitor]] pattern roughly corresponds to a [[catamorphism]], or [[fold (higher-order function)|fold]].

Similarly, the idea of immutable data from functional programming is often included in imperative programming languages,<ref>{{cite book |title=Effective Java |edition=Second |first=Joshua |last=Bloch |chapter=Item 15: Minimize Mutability |isbn=978-0321356680 |date=2008 |publisher=Addison-Wesley |url-access=registration |url=https://archive.org/details/effectivejava00bloc_0}}</ref> for example the tuple in Python, which is an immutable array, and Object.freeze() in JavaScript.<ref>{{Cite web|last=|first=|date=|title=Object.freeze() - JavaScript {{!}} MDN|url=https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/freeze|access-date=2021-01-04|website=developer.mozilla.org|quote=The Object.freeze() method freezes an object. A frozen object can no longer be changed; freezing an object prevents new properties from being added to it, existing properties from being removed, prevents changing the enumerability, configurability, or writability of existing properties, and prevents the values of existing properties from being changed. In addition, freezing an object also prevents its prototype from being changed. freeze() returns the same object that was passed in.}}</ref>