Editing Pattern matching (section)

{{Short description|Act of checking a given sequence of tokens for the presence of the constituents of some pattern}}
{{About|pattern matching in [[functional programming]]||string matching|and|pattern recognition}}
{{For|the use of variable matching criteria in defining abstract patterns to match|regular expression}}
{{More citations needed|date=February 2011}}
In [[computer science]], '''pattern matching''' is the act of checking a given sequence of [[Lexical analysis#Token|tokens]] for the presence of the constituents of some [[pattern]]. In contrast to [[pattern recognition]], the match usually must be exact: "either it will or will not be a  match." The patterns generally have the form of either [[String (computer science)|sequences]] or [[tree structure]]s. Uses of pattern matching include outputting the locations (if any) of a pattern within a token sequence, to output some component of the matched pattern, and to substitute the matching pattern with some other token sequence (i.e., [[Regular expression|search and replace]]).

Sequence patterns (e.g., a text string) are often described using [[regular expression]]s and matched using techniques such as [[backtracking]].

Tree patterns are used in some [[programming language]]s as a general tool to process data based on its structure, e.g. [[C Sharp (programming language)|C#]],<ref>{{cite web|url=https://docs.microsoft.com/en-us/dotnet/csharp/pattern-matching|title=Pattern Matching - C# Guide|date=13 March 2024}}</ref> [[F Sharp (programming language)|F#]],<ref>{{cite web|url=https://docs.microsoft.com/en-us/dotnet/fsharp/language-reference/pattern-matching|title=Pattern Matching - F# Guide|date=5 November 2021}}</ref> [[Haskell]],<ref>[http://www.haskell.org/tutorial/patterns.html A Gentle Introduction to Haskell: Patterns]</ref> [[Java (programming language)|Java]],<ref>https://docs.oracle.com/en/java/javase/21/language/pattern-matching.html</ref> [[ML (programming language)|ML]], [[Python (programming language)|Python]],<ref>{{Cite web|title=What's New In Python 3.10 — Python 3.10.0b3 documentation|url=https://docs.python.org/3.10/whatsnew/3.10.html#pep-634-structural-pattern-matching|access-date=2021-07-06|website=docs.python.org}}</ref> [[Ruby (programming language)|Ruby]],<ref>{{Cite web|title=pattern_matching - Documentation for Ruby 3.0.0|url=https://docs.ruby-lang.org/en/3.0.0/doc/syntax/pattern_matching_rdoc.html|access-date=2021-07-06|website=docs.ruby-lang.org}}</ref> [[Rust (programming language)|Rust]],<ref>{{cite web |url=https://doc.rust-lang.org/book/ch18-03-pattern-syntax.html |title=Pattern Syntax - The Rust Programming Language}}</ref> [[Scala (programming language)|Scala]],<ref>{{Cite web|title=Pattern Matching|url=https://docs.scala-lang.org/tour/pattern-matching.html|access-date=2021-01-17|website=Scala Documentation}}</ref> [[Swift (programming language)|Swift]]<ref>{{cite web|url=https://docs.swift.org/swift-book/ReferenceManual/Patterns.html|title=Patterns — The Swift Programming Language (Swift 5.1)}}</ref> and the symbolic mathematics language [[Wolfram Mathematica|Mathematica]] have special [[Syntax (programming languages)|syntax]] for expressing tree patterns and a [[language construct]] for [[Conditional (computer programming)|conditional execution]] and value retrieval based on it.

Often it is possible to give alternative patterns that are tried one by one, which yields a powerful conditional programming construct. Pattern matching sometimes includes support for [[Guard (computer science)|guards]].{{citation needed|date=January 2019}}