First-class function: Difference between revisions

Revision as of 18:32, 27 September 2021

Revision as of 01:18, 17 October 2021

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{{Short description|Programming language feature that allows manipulating functions like other values}}

In [[computer science]], a [[programming language]] is said to have '''first-class functions''' if it treats [[function (programming)|function]]s as [[first-class citizen]]s. This means the language supports passing functions as arguments to other functions, returning them as the values from other functions, and assigning them to variables or storing them in data structures.<ref>{{cite book|first1=Harold|last1=Abelson|authorlink1=Harold Abelson|first2=Gerald Jay|last2=Sussman|authorlink2=Gerald Jay Sussman|title=Structure and Interpretation of Computer Programs|at=[https://archive.org/details/structureinterpr00abel/page/ Formulating Abstractions with Higher-Order Procedures]|publisher=MIT Press|year=1984|isbn=0-262-01077-1|url=https://mitpress.mit.edu/sites/default/files/sicp/full-text/book/book-Z-H-12.html#%_sec_1.3}}</ref> Some programming language theorists require support for [[anonymous function]]s (function literals) as well.<ref name="test">[http://www.worldcat.org/oclc/222529448 Programming language pragmatics], by Michael Lee Scott, section 11.2 "Functional Programming".</ref> In languages with first-class functions, the [[name (computer science)|names]] of functions do not have any special status; they are treated like ordinary [[variable (computer science)|variable]]s with a [[function type]].<ref>{{cite journal |title=The Implementation of Lua 5.0 |author1=Roberto Ierusalimschy |author1-link=Roberto Ierusalimschy |author2=Luiz Henrique de Figueiredo |author3=Waldemar Celes |journal=Journal of Universal Computer Science |doi=10.3217/jucs-011-07-1159 |doi-access=free |volume=11 |issue=7 |date=2005 |pages=1159–1176}}</ref> The term was coined by [[Christopher Strachey]] in the context of "functions as first-class citizens" in the mid-1960s.<ref name=strachey>{{cite journal|last1=Burstall |first1=Rod |last2=Strachey |first2=Christopher |title=Understanding Programming Languages |journal=[[Higher-Order and Symbolic Computation]] |date=2000 |volume=13 |issue=52 |pages=11–49 |doi=10.1023/A:1010052305354 |s2cid=1989590 |url=http://www.cs.cmu.edu/~crary/819-f09/Strachey67.pdf |url-status=bot: unknown |archiveurl=https://web.archive.org/web/20100216060948/http://www.cs.cmu.edu/~crary/819-f09/Strachey67.pdf |archivedate=February 16, 2010 }} (also on 2010-02-16</ref>

First-class functions are a necessity for the [[functional programming]] style, in which the use of [[higher-order function]]s is a standard practice. A simple example of a higher-ordered function is the ''[[map (higher-order function)|map]]'' function, which takes, as its arguments, a function and a list, and returns the list formed by applying the function to each member of the list. For a language to support ''map'', it must support passing a function as an argument.

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| [[ALGOL 60]] || {{yes}} || {{no}} || {{yes}} || {{no}} || {{partial|Downwards}} || {{no}} || rowspan=6 | Have [[function type]]s.

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| [[ALGOL 68]] || {{yes}} || {{Partial|Yes}}<ref name=compa68pascal>{{cite journal|page=319|title=A comparison of PASCAL and Algol 68|journal=The Computer Journal|volume=21|number=4|year=1977|first=A.S.|last=Tanenbaum|doi=10.1093/comjnl/21.4.316|doi-access=free}}</ref> || {{yes}} || {{yes}} || {{partial|Downwards}}<ref>{{Cite web|url=http://python-history.blogspot.nl/2009/04/origins-of-pythons-functional-features.html?showComment=1243166621952#c702829329923892023|title = The History of Python: Origins of Python's "Functional" Features|date = 21 April 2009}}</ref> || {{no}}

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| [[Pascal (programming language)|Pascal]] || {{yes}} || {{no}} || {{yes}} || {{no}} || {{partial|Downwards}} || {{no}}

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| rowspan=9 | Functional languages || [[Lisp (programming language)|Lisp]] || {{partial|Syntax}} || {{partial|Syntax}} || {{yes}} || {{yes}} || {{partial|Common Lisp}} || {{no}} || (see below)

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| [[Scheme (programming language)|Scheme]] || {{yes}} || {{yes}} || {{yes}} || {{yes}} || {{yes}} || {{yes|SRFI 26}}<ref>{{Cite web|url=http://srfi.schemers.org/srfi-26/srfi-26.html|title=SRFI 26: Notation for Specializing Parameters without Currying}}</ref> ||

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| [[Julia (programming language)|Julia]] || {{yes}} || {{yes}} || {{yes}} || {{yes}} || {{yes}} || {{yes}} ||

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| [[Io (programming language)|Io]] || {{yes}} || {{yes}} || {{yes}} || {{yes}} || {{yes}} || {{no}} ||

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| [[JavaScript]] || {{yes}} || {{yes}} || {{yes}} || {{yes}} || {{yes}} || {{yes|ECMAScript 5}} || Partial application possible with user-land code on ES3 <ref>{{Cite web|url=http://ejohn.org/blog/partial-functions-in-javascript/|title=John Resig - Partial Application in JavaScript}}</ref>

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| [[Lua (programming language)|Lua]] || {{yes}} || {{yes}} || {{yes}} || {{yes}} || {{yes}} || {{yes}}<ref>{{cite web |last1=Katz |first1=Ian |url=http://tinylittlelife.org/?p=249 |title=Lua Code for Curry (Currying Functions) |date=2010-07-23 |df=mdy |archive-url=https://web.archive.org/web/20181106235506/http://tinylittlelife.org/?p=249 |archive-date=2018-11-06}}</ref> ||

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| [[Perl]] || {{yes}} || {{yes}} || {{yes|6}} || {{yes}} || {{yes}} || {{yes|6}}<ref>{{Cite web|url=http://perlgeek.de/blog-en/perl-5-to-6/28-currying.html|title = Blog &#124; Perlgeek.de :: Currying}}</ref> ||

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| [[Python (programming language)|Python]] || {{yes}} || {{yes}} || {{yes}} || {{partial|Expressions only}} || {{yes}} || {{yes|2.5}}<ref>{{Cite web|url=https://docs.python.org/whatsnew/2.5.html#pep-309-partial-function-application|title=What's New in Python 2.5 — Python 3.10.0 documentation}}</ref> || (see below)

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| [[Ruby (programming language)|Ruby]] || {{partial|Syntax}} || {{partial|Syntax}} || {{no|Unscoped}} || {{yes}} || {{yes}} || {{partial|1.9}} || (see below)

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| [[Mathematica]] || {{yes}} || {{yes}} || {{yes}} || {{yes}} || {{yes}} || {{no}} ||

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| [[MATLAB]] || {{yes}} || {{yes}} || {{yes}} || {{yes}}<ref>{{Cite web|url=http://www.mathworks.co.uk/help/matlab/matlab_prog/anonymous-functions.html|title=Anonymous Functions - MATLAB & Simulink - MathWorks United Kingdom}}</ref> || {{yes}} || {{yes}} || Partial application possible by automatic generation of new functions.<ref>[https://stackoverflow.com/q/9154271 Partial Function Evaluation in MATLAB]</ref>

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| [[Smalltalk]] || {{yes}} || {{yes}} || {{yes}} || {{yes}} || {{yes}} || {{partial}} || Partial application possible through library.