Dynamic programming language: Difference between revisions

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}}let foo = 42; // foo is now a number

A '''dynamic programming language''' is a type of programming language that allows various operations to be determined and executed at runtime. This is different from the compilation phase. Key decisions about variables, method calls, or data types are made when the program is running, unlike in [[Static program analysis|static languages]], where the structure and types are fixed during compilation. Dynamic languages provide flexibility. This allows developers to write more adaptable and concise code.

foo = "bar"; // foo is now a string

foo = true; // foo is now a boolean

In computer science, a '''dynamic programming language''' is a class of high-level programming languages which at runtime execute many common programming behaviours that static programming languages perform during compilation. These behaviors could include an extension of the program, by adding new code, by extending objects and definitions, or by modifying the type system. Although similar behaviors can be emulated in nearly any language, with varying degrees of difficulty, complexity and performance costs, dynamic languages provide direct tools to make use of them. Many of these features were first implemented as native features in the Lisp programming language.

For instance, in a dynamic language, a variable can start as an integer. It can later be reassigned to hold a string without explicit type declarations. This feature of dynamic typing enables more fluid and less restrictive coding. Developers can focus on the logic and functionality rather than the constraints of the language.

Most dynamic languages are also dynamically typed, but not all are. Dynamic languages are frequently (but not always) referred to as scripting languages, although that term in its narrowest sense refers to languages specific to a given run-time environment.

==Implementation==

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===Eval===

Some dynamic languages offer an ''[[eval]]'' function. This function takes a string or [[abstract syntax tree]] containing code in the language and executes it. If this code stands for an expression, the resulting value is returned. [[Erik Meijer (computer scientist)|Erik Meijer]] and Peter Drayton distinguish the [[runtime code generation]] offered by eval from the [[dynamic loading]] offered by [[shared libraries]], and warn that in many cases eval is used merely to implement [[higher-order function]]s (by passing functions as strings) or [[deserialization]].<ref>{{Citation | citeseerx = 10.1.1.69.5966 | title=Static Typing Where Possible, Dynamic Typing When Needed: The End of the Cold War Between Programming Languages | author=[[Erik Meijer (computer scientist)|Meijer, Erik]] and Peter Drayton | year=2005 | publisher=[[Microsoft]] Corporation|url=https://people.dsv.su.se/~beatrice/DYPL/meijer_drayton.pdf}}</ref>

===Object runtime alteration===

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[[Assembly language|Assembly]], [[C (programming language)|C]], [[C++]], early [[Java (programming language)|Java]], and [[Fortran]] do not generally fit into this category.{{clarify|date=September 2016}}

The earliest dynamic programming language is considered to be Lisp (McCarthy, 1965) which continued to influence the design of programming languages to the present day.<ref>{{cite book| last=Harper| first=Robert | title=Practical Foundations for Programming languages | page=195 | year=2016 |publisher=Cambridge University Press| ___location=New York| isbn=9-781107-150300}}</ref>

==Example code==

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* [[ActionScript]]

* [[BeanShell]]<ref>[http://static.springsource.org/spring/docs/2.0.x/reference/dynamic-language.html Chapter 24. Dynamic language support]. Static.springsource.org. Retrieved on 2013-07-17.</ref>

* [[C Sharp (programming language)|C#]] (using Reflectionreflection)]]

* [[Clojure]]

* [[CobolScript]]

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* [[Elixir (programming language)|Elixir]]

* [[Erlang (programming language)|Erlang]]

* [[Forth (programming language)|FORTHForth]]

* [[Gambas]]

* [[GDScript]]

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* [[MATLAB]] / [[GNU Octave|Octave]]

* [[Objective-C]]

* [[Object REXX|ooRexx]]

* [[Perl]]

* [[PHP]]

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* [[Raku (programming language)|Raku]]

* [[Rebol]]

* [[Ring (programming language)|Ring]]

* [[Ruby (programming language)|Ruby]]

* [[Smalltalk]]

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** {{cite web |last1=Ascher |first1=David |date=2004-07-27 |df=mdy |url=https://www.activestate.com/Corporate/Publications/ActiveState_Dynamic_Languages.pdf |title=Dynamic Languages — ready for the next challenges, by design |department=Whitepapers |publisher=[[ActiveState]] |archive-url=https://web.archive.org/web/20081118035341/https://www.activestate.com/Corporate/Publications/ActiveState_Dynamic_Languages.pdf |archive-date=2008-11-18}}

** {{cite web |last1=Ascher |first1=David |date=2004-07-27 |df=mdy |url=http://www.activestate.com/company/newsroom/whitepapers_ADL.plex |title=Dynamic Languages — ready for the next challenges, by design |department=Whitepapers |publisher=[[ActiveState]] |archive-url=https://web.archive.org/web/20081208121835/http://www.activestate.com/company/newsroom/whitepapers_ADL.plex |archive-date=2008-12-08}}

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{{Types of programming languages}}