37.154.166.127: /* Multiple implementations */

2025-05-16T12:53:11Z

Multiple implementations

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{{short description|System for executing computer programs}}

In [[computer programming]], a '''programming language implementation''' is a system for executing [[computer programs]]. There are two general approaches to programming language implementation:<ref name="RantaBook">{{cite book |last1=Ranta |first1=Aarne |title=Implementing Programming Languages |date=February 6, 2012 |publisher=College Publications |isbn=9781848900646 |pages=16–18 |url=http://www.cse.chalmers.se/edu/year/2012/course/DAT150/lectures/plt-book.pdf#page=16 |access-date=22 March 2020 |url-status=live |archive-url=https://web.archive.org/web/20201107224313/http://www.cse.chalmers.se/edu/year/2012/course/DAT150/lectures/plt-book.pdf#page=16 |archive-date= Nov 7, 2020 }}</ref>
*''[[Interpreter (computing)|Interpretation]]:'' The program is read as input by an interpreter, which performs the actions written in the program.<ref name="LanguageGreg">{{cite web |last1=Baker |first1=Greg |title=Language Implementations |url=https://www2.cs.sfu.ca/~ggbaker/prog-langs/content/lang-implement.html |website=Computing Science - Simon Fraser University |access-date=22 March 2020 |url-status=live |archive-url= https://web.archive.org/web/20190308033517/http://www.cs.sfu.ca/~ggbaker/prog-langs/content/lang-implement.html |archive-date= Mar 8, 2019 }}</ref>
*''[[Compiler|Compilation]]:'' The program is read by a compiler, which translates it into some other language, such as [[bytecode]] or [[machine code]]. The translated code may either be directly [[Execution (computing)|executed]] by hardware or serve as input to another interpreter or another compiler.<ref name="LanguageGreg" />

==Interpreter==
{{Main|Interpreter (computing)}}
An [[interpreter (computing)|interpreter]] is composed of two parts: a [[parser]] and an [[evaluator]]. After a program is read as input by an interpreter, it is processed by the parser. The parser breaks the program into [[Syntax (programming languages)|language components]] to form a [[parse tree]]. The evaluator then uses the parse tree to execute the program.<ref name="IntroToComputing">{{cite book |last1=Evans |first1=David |title=Introduction to Computing |date=19 August 2011 |publisher=University of Virginia |page=211 |url=https://computingbook.org/FullText.pdf#page=221 |access-date=22 March 2020}}</ref>

===Virtual machine===
A [[virtual machine]] is a special type of interpreter that interprets bytecode.<ref name="LanguageGreg" /> Bytecode is a [[Cross-platform software|portable]] low-level code similar to machine code, though it is generally executed on a virtual machine instead of a physical machine.<ref name="MakeUseOfVM">{{cite web |last1=Sridhar |first1=Jay |title=Why the Java Virtual Machine Helps Your Code Run Better |url=https://www.makeuseof.com/tag/why-java-virtual-machine-code-run-better/ |date=Aug 29, 2017 |website=MakeUseOf |access-date=22 March 2020}}</ref> To improve their efficiencies, many programming languages such as [[Java (programming language)|Java]],<ref name="MakeUseOfVM" /> [[Python (programming language)|Python]],<ref name="PythonBytecode">{{cite web |last1=Bennett |first1=James |title=An introduction to Python bytecode |url=https://opensource.com/article/18/4/introduction-python-bytecode |date=April 23, 2018 |website=Opensource.com |access-date=22 March 2020}}</ref> and [[C Sharp (programming language)|C#]]<ref name="CLR">{{cite web |last1=Ali |first1=Mirza Farrukh |title=Common Language Runtime(CLR) DotNet |url=https://medium.com/@mirzafarrukh13/common-language-runtime-dotnet-83e0218edcae |date=Oct 12, 2017 |website=Medium |access-date=22 March 2020}}</ref> are compiled to bytecode before being interpreted.

===Just-in-time compiler===
Some virtual machines include a [[just-in-time compilation|just-in-time (JIT) compiler]] to improve the efficiency of bytecode execution. While the bytecode is being executed by the virtual machine, if the JIT compiler determines that a portion of the bytecode will be used repeatedly, it compiles that particular portion to machine code. The JIT compiler then stores the machine code in [[Random-access memory|memory]] so that it can be used by the virtual machine. JIT compilers try to strike a balance between longer compilation time and faster execution time.<ref name="LanguageGreg" />

==Compiler==
{{Main|Compiler}}
A [[compiler]] translates programs written in one language into another language. Most compilers are organized into three stages: a [[Compiler#Front end|front end]], an [[Compiler#Middle end|optimizer]], and a [[Compiler#Back end|back end]]. The front end is responsible for understanding the program. It makes sure a program is valid and transforms it into an [[intermediate representation]], a data structure used by the compiler to represent the program. The optimizer improves the intermediate representation to increase the speed or reduce the size of the [[executable]] which is ultimately produced by the compiler. The back end converts the optimized intermediate representation into the output language of the compiler.<ref name="EngineeringCompiler">{{cite book |last1=Cooper |first1=Keith |last2=Torczon |first2=Linda |title=Engineering a Compiler |url=https://archive.org/details/engineeringcompi00coop_143 |url-access=limited |date=7 February 2011 |publisher=Morgan Kaufmann |isbn=9780120884780 |pages=[https://archive.org/details/engineeringcompi00coop_143/page/n238 6]-9 |edition=2nd}}</ref>

If a compiler of a given [[high level language]] produces another high level language, it is called a [[Source-to-source compiler|transpiler]]. Transpilers can be used to extend existing languages or to simplify compiler development by exploiting [[Software portability|portable]] and well-optimized implementations of other languages (such as [[C (programming language)|C]]).<ref name="LanguageGreg" />

Many combinations of interpretation and compilation are possible, and many modern programming language implementations include elements of both. For example, the [[Smalltalk]] programming language is conventionally implemented by compilation into [[bytecode]], which is then either interpreted or compiled by a [[virtual machine]]. Since Smalltalk bytecode is run on a virtual machine, it is portable across different hardware platforms.<ref name="SmalltalkBook">{{cite book |last1=Lewis |first1=Simon |title=The Art and Science of Smalltalk |date=May 11, 1995 |publisher=Prentice Hall |isbn=9780133713459 |pages=20–21 |url=http://sdmeta.gforge.inria.fr/FreeBooks/Art/artAdded174186187Final.pdf#page=32 |access-date=23 March 2020}}</ref>

==Multiple implementations==
Programming languages can have multiple implementations. Different implementations can be written in different languages and can use different methods to compile or interpret code. For example, implementations of [[Python (programming language)|Python]] include:{{thinsp}}<ref name="AltPython">{{cite web |title=Alternative Python Implementations |url=https://www.python.org/download/alternatives/ |website=Python.org |access-date=23 March 2020}}</ref>
* [[CPython]], the [[reference implementation]] of Python
* [[IronPython]], an implementation targeting the [[.NET Framework]] (written in [[C Sharp (programming language)|C#]])
* [[Jython]], an implementation targeting the [[Java virtual machine]]
* [[PyPy]], an implementation designed for speed (written in RPython)

==References==
{{Reflist}}

==External links==
*{{Commons category-inline|Compiling and linking}}

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[[Category:Programming language implementation| ]]
[[Category:Programming language topics|Implementation]]

Programming language implementation - Revision history

37.154.166.127: /* Multiple implementations */