Functional programming

In computer science, functional programming is a programming paradigm where programs are constructed by applying and composing functions. It is a declarative programming paradigm in which function definitions are trees of expressions that map values to other values, rather than a sequence of imperative statements which update the running state of the program.

In functional programming, functions are treated as first-class citizens, meaning that they can be bound to names (including local identifiers), passed as arguments, and returned from other functions, just as any other data type can. This allows programs to be written in a declarative and composable style, where small functions are combined in a modular manner.

Functional programming is sometimes treated as synonymous with purely functional programming, a subset of functional programming which treats all functions as deterministic mathematical functions, or pure functions. When a pure function is called with some given arguments, it will always return the same result, and cannot be affected by any mutable state or other side effects. This is in contrast with impure procedures, common in imperative programming, which can have side effects (such as modifying the program's state or taking input from a user). Proponents of purely functional programming claim that by restricting side effects, programs can have fewer bugs, be easier to debug and test, and be more suited to formal verification.[1][2]

Functional programming has its roots in academia, evolving from the lambda calculus, a formal system of computation based only on functions. Functional programming has historically been less popular than imperative programming, but many functional languages are seeing use today in industry and education, including Common Lisp, Scheme,[3][4][5][6] Clojure, Wolfram Language,[7][8] Racket,[9] Erlang,[10][11][12] Elixir,[13] OCaml,[14][15] Haskell,[16][17] and F#.[18][19] Functional programming is also key to some languages that have found success in specific domains, like JavaScript in the Web,[20] R in statistics,[21][22] J, K and Q in financial analysis, and XQuery/XSLT for XML.[23][24] Domain-specific declarative languages like SQL and Lex/Yacc use some elements of functional programming, such as not allowing mutable values.[25] In addition, many other programming languages support programming in a functional style or have implemented features from functional programming, such as C++11, C#,[26] Kotlin,[27] Perl,[28] PHP,[29] Python,[30] Go,[31] Rust,[32] Raku,[33] Scala,[34] and Java (since Java 8).[35]

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  18. ^ Mansell, Howard (2008). Quantitative Finance in F#. CUFP 2008. Retrieved 2009-08-29.
  19. ^ Peake, Alex (2009). The First Substantial Line of Business Application in F#. CUFP 2009. Archived from the original on 2009-10-17. Retrieved 2009-08-29.
  20. ^ comments, 27 Jun 2017 Matt Banz Feed 603up 2. "An introduction to functional programming in JavaScript". Opensource.com. Retrieved 2021-01-09.{{cite web}}: CS1 maint: numeric names: authors list (link)
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  26. ^ Functional Programming with C# - Simon Painter - NDC Oslo 2020, archived from the original on 2021-10-30, retrieved 2021-10-23
  27. ^ "Functional programming - Kotlin Programming Language". Kotlin. Retrieved 2019-05-01.
  28. ^ Dominus, Mark J. (2005). Higher-Order Perl. Morgan Kaufmann. ISBN 978-1-55860-701-9.
  29. ^ Holywell, Simon (2014). Functional Programming in PHP. php[architect]. ISBN 9781940111056.
  30. ^ The Cain Gang Ltd. "Python Metaclasses: Who? Why? When?" (PDF). Archived from the original (PDF) on 30 May 2009. Retrieved 27 June 2009.
  31. ^ "GopherCon 2020: Dylan Meeus - Functional Programming with Go". YouTube.
  32. ^ "Functional Language Features: Iterators and Closures - The Rust Programming Language". doc.rust-lang.org. Retrieved 2021-01-09.
  33. ^ Vanderbauwhede, Wim (18 July 2020). "Cleaner code with functional programming". Archived from the original on 28 July 2020. Retrieved 6 October 2020.
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