High-level programming language: Difference between revisions

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A '''high-level programming language''' is a [[programming language]] with strong [[Abstraction (computer science)|abstraction]] from the details of the [[computer]]. In contrast to [[low-level programming language]]s, it may use [[natural language]] ''elements'', be easier to use, or may automate (or even hide entirely) significant areas of computing systems (e.g. [[memory management]]), making the process of developing a program simpler and more understandable than when using a lower-level language. The amount of abstraction provided defines how "high-level" a programming language is.<ref>{{cite web |archive-url=https://web.archive.org/web/20070826224349/http://www.ittc.ku.edu/hybridthreads/glossary/index.php |archive-date=2007-08-26 |url=http://www.ittc.ku.edu/hybridthreads/glossary/index.php |url-status=dead |title=HThreads - RD Glossary<!-- Bot generated title -->}}</ref>

''High-level'' refers to a level of abstraction from the hardware details of a [[CPU |processor]] inherent in [[machine code |machine]] and [[assembly language| assembly]] code. Rather than dealing with registers, memory addresses, and call stacks, high-level languages deal with variables, arrays, [[object (computer science)|object]]s, arithmetic and [[Boolean expression]]s, [[function (computing)|functions]], loops, [[Thread (computer science)|thread]]s, locks, and other computer science abstractions, intended to facilitate [[Correctness (computer science)|correctness]] and [[software maintenance |maintainability]]. Unlike low-level [[assembly language]]s, high-level languages have few, if any, language elements that translate directly intoto a machine's native [[opcode]]s. Other features, such as string handling routines, [[Object-oriented programming|object-oriented language]] features, and file input/output, may also be presentprovided. One thing to note aboutA high-level programminglanguage languagesallows isfor thatsource thesecode languagesthat allow the programmer to beis detached and separated from the machine details. That is, unlike low-level languages like assembly orand machine languagecode, high-level programminglanguage cancode amplifymay theresult programmer's instructions and trigger a lot ofin data movements inwithout the background without theirprogrammer's knowledge. TheSome responsibility and powercontrol of executingwhat instructions haveto beenexecute is handed over to the machine from the programmercompiler.

==History==

In the 1960s, a high-level programming language using a [[compiler]] was commonly called an ''[[autocode]]''.<ref name=kleith>{{cite book|last=London|first=Keith|year=1968|title=Introduction to Computers|publisher=Faber and Faber Limited|___location=24 Russell Square London WC1|isbn=0571085938|page=184|chapter=4, Programming|quote=The 'high' level programming languages are often called autocodes and the processor program, a compiler.}}<!--The book has no ISBN number, instead it has an SBN number. There is no typo in the prior sentence.--></ref>

Examples of autocodes are [[COBOL]] and [[Fortran]].<ref name=kleith2>{{cite book|last=London|first=Keith|title=Introduction to Computers|year=1968|publisher=Faber and Faber Limited|___location=24 Russell Square London WC1|isbn=0571085938|page=186|chapter=4, Programming|quote=Two high level programming languages which can be used here as examples to illustrate the structure and purpose of autocodes are COBOL (Common Business Oriented Language) and FORTRAN (Formular Translation).}}<!--The book has no ISBN number, instead it has an SBN number. There is no typo in the prior sentence.--></ref>

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The first high-level programming language designed for computers was [[Plankalkül]], created by [[Konrad Zuse]].<ref>{{ill|Wolfgang Giloi{{!}}Giloi, Wolfgang, K.|de|Wolfgang Giloi}} (1997). "Konrad Zuse's Plankalkül: The First High-Level "non von Neumann" Programming Language". IEEE Annals of the History of Computing, vol. 19, no. 2, pp.&nbsp;17–24, April–June, 1997. [http://doi.ieeecomputersociety.org/10.1109/85.586068 (abstract)]</ref> However, it was not implemented in his time, and his original contributions were largely isolated from other developments due to [[World War II]], aside from the language's influence on the "Superplan" language by [[Heinz Rutishauser]] and also to some degree [[ALGOL]]. The first significantly widespread high-level language was [[Fortran]], a machine-independent development of IBM's earlier [[Autocode]] systems. The [[ALGOL]] family, with [[ALGOL 58]] defined in 1958 and [[ALGOL 60]] defined in 1960 by committees of European and American computer scientists, introduced [[recursion]] as well as [[nested functions]] under [[lexical scope]]. ALGOL 60 was also the first language with a clear distinction between [[call by value|value]] and [[call by name|name-parameter]]s and their corresponding [[Semantics (computer science)|semantics]].<ref>Although it lacked a notion of [[call by reference|reference-parameter]]s, which could be a problem in some situations. Several successors, including [[ALGOL W]], [[ALGOL 68]], [[Simula]], [[Pascal (programming language)|Pascal]], [[Modula]] and [[Ada (programming language)|Ada]] thus included reference-parameters (The related C-language family instead allowed addresses as <code>value</code>-parameters).</ref> ALGOL also introduced several [[structured programming]] concepts, such as the <code>while-do</code> and <code>if-then-else</code> constructs and its [[Syntax (programming languages)|syntax]] was the first to be described in formal notation – ''[[Backus–Naur form]]'' (BNF). During roughly the same period, [[COBOL]] introduced [[Record (computer science)|record]]s (also called structs) and [[Lisp (programming language)|Lisp]] introduced a fully general [[lambda abstraction]] in a programming language for the first time.

== Abstraction penalty ==

== Features ==

A high-level language provides features that standardize common tasks, permit rich debugging, and maintain architectural agnosticism. On the other hand, a low-level language requires the coder to work at a lower-level of abstraction which is generally more challenging, but does allow for [[program optimization |optimizations]] that are not possible with a high-level language. This ''abstraction penalty'' for using a high-level language instead of a low-level language is real, but in practice, low-level optimizations rarely improve performance at the [[user experience]] level.<ref>{{cite journal

''High-level'' refers to a level of abstraction from the hardware details of a [[CPU |processor]] inherent in [[machine code |machine]] and [[assembly language| assembly]] code. Rather than dealing with registers, memory addresses, and call stacks, high-level languages deal with variables, arrays, [[object (computer science)|object]]s, arithmetic and [[Boolean expression]]s, [[function (computing)|functions]], loops, [[Thread (computer science)|thread]]s, locks, and other computer science abstractions, intended to facilitate [[Correctness (computer science)|correctness]] and [[software maintenance |maintainability]]. Unlike low-level [[assembly language]]s, high-level languages have few, if any, language elements that translate directly into a machine's native [[opcode]]s. Other features, such as string handling routines, [[Object-oriented programming|object-oriented language]] features, and file input/output, may also be present. One thing to note about high-level programming languages is that these languages allow the programmer to be detached and separated from the machine. That is, unlike low-level languages like assembly or machine language, high-level programming can amplify the programmer's instructions and trigger a lot of data movements in the background without their knowledge. The responsibility and power of executing instructions have been handed over to the machine from the programmer.

== Abstraction penalty ==

High-level languages intend to provide features that standardize common tasks, permit rich debugging, and maintain architectural agnosticism; while low-level languages often produce more efficient code through [[program optimization|optimization]] for a specific [[Computer architecture|system architecture]]. ''Abstraction penalty'' is the cost that high-level programming techniques pay for being unable to optimize performance or use certain hardware because they don't take advantage of certain low-level architectural resources. High-level programming exhibits features like more generic data structures and operations, run-time interpretation, and intermediate code files; which often result in execution of far more operations than necessary, higher memory consumption, and larger binary program size.<ref>{{cite journal

|author=Surana P

|title=Meta-Compilation of Language Abstractions.

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| pages = 367

| publisher = Springer

}}</ref> ForNone thisthe reasonless, code whichthat needs to run particularly quickly and efficiently may require the use of a lower-level language, even if a higher-level language would make the coding easier to write and maintain. In many cases, critical portions of a program mostly in a high-level language canare be hand-coded in [[assembly language]],in leadingorder to meet tight timing or memory constraints. A well-designed compiler for a muchhigh-level faster,language morecan efficientproduce code comparable in efficiency to what could be coded by hand in assembly, orand simplythe reliablyhigher-level functioningabstractions [[Programsometimes optimisation|optimisedallow program]]for optimizations that beat the performance of hand-coded assembly.<ref>

However, with the growing complexity of modern [[microprocessor]] architectures, well-designed compilers for high-level languages frequently produce code comparable in efficiency to what most low-level programmers can produce by hand, and the higher abstraction may allow for more powerful techniques providing better overall results than their low-level counterparts in particular settings.<ref>

{{Cite journal

|author1=Manuel Carro |author2=José F. Morales |author3=Henk L. Muller |author4=G. Puebla |author5=M. Hermenegildo | journal = Proceedings of the 2006 International Conference on Compilers, Architecture and Synthesis for Embedded Systems

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| year = 2006

| publisher = ACM

}}</ref> Since a high-level language is designed independent of a specific computing [[Computer architecture |system architecture]], a program written in such a language can run on any computing context with a compatible compiler or interpreter.

}}</ref>

High-level languages are designed independent ofUnlike a specificlow-level computinglanguage [[Computerthat architecture|systemis architecture]].inherently Thistied facilitatesto executingprocessor a program written in suchhardware, a language on any computing system with compatible support for the Interpreted or [[Just-in-time compilation|JIT]] program. Highhigh-level languageslanguage can be improved, as their designers develop improvements. In other cases,and new high-level languages can evolve from one or more others with the goal of aggregating the most popular constructs with new or improved features. AnFor example of this is, [[Scala (programming language)|Scala]] which maintains backward compatibility with [[Java (programming language)|Java]],. meaning that programs and librariesCode written in Java will continue to be usable even if a programming shopdeveloper switches to Scala;. thisThis makes the transition easier and extends the lifespan of sucha high-level coding indefinite[[codebase]]. In contrast, low-level programs rarely survive beyond the [[Computer architecture |system architecture]] which they were written for without major revision. This is the engineering 'trade-off' for the 'Abstraction Penalty'.

== Relative meaning ==

{{refimprove section|small=y|date=October 2018}}

Examples of high-level programming languages in active use today include [[Python (programming language)|Python]], [[JavaScript]], [[Visual Basic]], [[Delphi (programming language)|Delphi]], [[Perl]], [[PHP]], [[ECMAScript]], [[Ruby (programming language)|Ruby]], [[C Sharp (programming language)|C#]], [[Java (programming language)|Java]] and many others.

The terms ''high-level'' and ''low-level'' are inherently relative, and languages can be compared as higher or lower level to each other. Sometimes the [[C (programming language)|C language]] is considered as either high-level or low-level depending on one's perspective. Regardless, most agree that C is higher level than assembly and lower level than most other languages.

The terms ''high-level'' and ''low-level'' are inherently relative. Some decades ago,{{clarify timeframe|date=July 2023}} the [[C (programming language)|C language]], and similar languages, were most often considered "high-level", as it supported concepts such as expression evaluation, [[parameter]]ised recursive functions, and data types and structures, while [[assembly language]] was considered "low-level". Today, many programmers might refer to C as low-level, as it lacks a large [[Runtime system|runtime-system]] (no garbage collection, etc.), basically supports only scalar operations, and provides direct memory addressing; it therefore, readily blends with assembly language and the machine level of [[CPU]]s and [[microcontroller]]s. Also, in the introduction chapter of [[The C Programming Language]] (second edition) by [[Brian Kernighan]] and [[Dennis Ritchie]], C is described as "not a very high level" language.<ref>{{cite book|last1=Kernighan|first1=Brian W.|last2=Ritchie|first2=Dennis M.|date=1988|title=The C Programming Language: 2nd Edition|url=https://books.google.com/books?id=FGkPBQAAQBAJ|url-status=bot: unknown|publisher=Prentice Hall|isbn=9780131103627|archive-url=https://web.archive.org/web/20221025180501/https://books.google.com/books?id=FGkPBQAAQBAJ|archive-date=25 October 2022|access-date=25 October 2022}}</ref>

The terms ''high-level'' and ''low-level'' are inherently relative. Some decades ago,{{clarify timeframe|date=July 2023}} the [[C (programming language)|C language]], and similar languages, were most often considered "high-level", as it supportedsupports conceptsconstructs such as expression evaluation, [[parameter |parameterized]]ised and recursive functions, and data types and structures, whilewhich [[assemblyare language]]generally wasnot consideredsupported "low-level".in Today,assembly manyor programmersdirectly mightby refera toprocessor but C asdoes provide lowlower-level, asfeatures itsuch lacksas a large [[Runtime system|runtimeauto-system]]increment (noand garbagepointer collection, etcmath.), basicallyBut supportsC onlylacks scalarmany operations,higher-level andabstracts providescommon directin memoryother addressing;languages itsuch therefore,as readily[[garbage blends with assembly languagecollection]] and thea machinebuilt-in levelstring of [[CPU]]s and [[microcontroller]]stype. Also, inIn the introduction chapter of [[The C Programming Language]] (second edition) by [[Brian Kernighan]] and [[Dennis Ritchie]], C is described as "not a very high level" language.<ref>{{cite book|last1=Kernighan|first1=Brian W.|last2=Ritchie|first2=Dennis M.|date=1988|title=The C Programming Language: 2nd Edition|url=https://books.google.com/books?id=FGkPBQAAQBAJ|url-status=bot: unknown|publisher=Prentice Hall|isbn=9780131103627|archive-url=https://web.archive.org/web/20221025180501/https://books.google.com/books?id=FGkPBQAAQBAJ|archive-date=25 October 2022|access-date=25 October 2022}}</ref>

Assembly language may itself be regarded as a higher level (but often still one-to-one if used without [[Macro (computer science)|macro]]s) representation of [[machine code]], as it supports concepts such as constants and (limited) expressions, sometimes even variables, procedures, and [[data structure]]s. [[Machine code]], in turn, is inherently at a slightly higher level than the [[microcode]] or [[micro-operation]]s used internally in many processors.<ref>{{Cite book|title=The art of assembly language|last=Hyde, Randall.|date=2010|publisher=No Starch Press|isbn=9781593273019|edition= 2nd|___location=San Francisco|oclc=635507601|url=https://books.google.com/books?id=sYHtTvQ-ObIC}}</ref>

Assembly language is higher-level than machine code, but still highly tied to the processor hardware. But, assembly may provide some higher-level features such as [[Macro (computer science)|macro]]s, relatively limited expressions, constants, variables, procedures, and [[data structure]]s.

Assembly language may itself be regarded as a higher level (but often still one-to-one if used without [[Macro (computer science)|macro]]s) representation of [[machine code]], as it supports concepts such as constants and (limited) expressions, sometimes even variables, procedures, and [[data structure]]s. [[Machine code]], in turn, is inherently at a slightly higher level abstraction than the [[microcode]] or [[micro-operation]]s used internally in many processors.<ref>{{Cite book|title=The art of assembly language|last=Hyde, Randall.|date=2010|publisher=No Starch Press|isbn=9781593273019|edition= 2nd|___location=San Francisco|oclc=635507601|url=https://books.google.com/books?id=sYHtTvQ-ObIC}}</ref>

== Execution modes ==

{{refimprove section|find=Execution modes|date=October 2018}}

The source code of a high-level language may be processed in various ways, including

There are three general modes of execution for modern high-level languages:

; Interpreted: When code written in a language is [[Interpreted language|interpreted]], its syntax is read and then executed directly, with no compilation stage. A program called an ''interpreter'' reads each program statement, following the program flow, then decides what to do, and does it. A hybrid of an interpreter and a compiler will compile the statement into machine code and execute that; the machine code is then discarded, to be interpreted anew if the line is executed again. Interpreters are commonly the simplest implementations of the behavior of a language, compared to the other two variants listed here.

; Compiled: A [[compiler]] transforms source code into other code. Sometimes, and traditionally, a compiler generates native machine code that is interpreted by the processor. But, today many execution models involve generating an [[intermediate representation]] (i.e. [[bytecode]]) that is later interpreted in software or converted to native code at runtime (via [[JIT compilation]]).

; Compiled: When code written in a language is [[Compiled language|compiled]], its syntax is transformed into an executable form before running. There are two types of compilation:

:; Machine code generation: Some compilers compile source code directly into [[machine code]]. This is the original mode of compilation, and languages that are directly and completely transformed to machine-native code in this way may be called ''truly compiled'' languages. See [[assembly language]].

; Source-to-source translated or transcompiled[[Transpiled]]: Code written in a language may be translated into termssource code of aanother language (typically lower-level language) for which nativea codecompiler compilersor areinterpreter alreadyis commonavailable. [[JavaScript]] and the language [[C (programming language)|C]] are common targets for such translators. SeeFor [[CoffeeScript]]example, [[Chicken (Scheme implementation)|Chicken]] Scheme, and [[Eiffel (programming language)|Eiffel]] as examples. Specifically, the generated C and C++ code can be seen (as generated from the Eiffel languagecode when using the [[EiffelStudio]] IDE) in the EIFGENs directory of any compiled Eiffel project. In Eiffel, the ''translated'' process is referred to as ''transcompiling'' or ''transcompiled'', and the Eiffel compiler as a transcompiler or [[source-to-source compiler]].

:; Intermediate representations: When code written in a language is compiled to an [[intermediate representation]], that representation can be optimized or saved for later execution without the need to re-read the source file. When the intermediate representation is saved, it may be in a form such as [[bytecode]]. The intermediate representation must then be interpreted or further compiled to execute it. [[Virtual machine]]s that execute bytecode directly or transform it further into machine code have blurred the once clear distinction between intermediate representations and truly compiled languages.

; Source-to-source translated or transcompiled: Code written in a language may be translated into terms of a lower-level language for which native code compilers are already common. [[JavaScript]] and the language [[C (programming language)|C]] are common targets for such translators. See [[CoffeeScript]], [[Chicken (Scheme implementation)|Chicken]] Scheme, and [[Eiffel (programming language)|Eiffel]] as examples. Specifically, the generated C and C++ code can be seen (as generated from the Eiffel language when using the [[EiffelStudio]] IDE) in the EIFGENs directory of any compiled Eiffel project. In Eiffel, the ''translated'' process is referred to as transcompiling or transcompiled, and the Eiffel compiler as a transcompiler or [[source-to-source compiler]].

; Software interpreted: A [[interpreter (software)|software interpreter]] performs the actions encoded in source code without generating native machine code.

Alternatively,; itHardware isinterpreted: possibleAlthough foruncommon, a high-levelprocessor language to be directly implemented by a computer – the computer directly executes the HLL code. This is known aswith a ''[[high-level language computer architecture]]'' –can theprocess [[computera architecture]]high-level itselflanguage iswithout designeda tocompilation bestep. targetedFor byexample, a specific high-level language. Thethe [[Burroughs large systems]] were target machines for [[ALGOL 60]], for example.<ref>{{Citation|last=Chu|first=Yaohan|chapter=Concepts of High-Level Language Computer Architecture|date=1975|pages=1–14|publisher=Elsevier|isbn=9780121741501|doi=10.1016/b978-0-12-174150-1.50007-0|title=High-Level Language Computer Architecture}}</ref>

Note that languages are not strictly ''interpreted'' languages or ''compiled'' languages. Rather, implementations of language behavior use interpreting or compiling. For example, [[ALGOL 60]] and [[Fortran]] have both been interpreted (even though they were more typically compiled). Similarly, Java shows the difficulty of trying to apply these labels to languages, rather than to implementations; Java is compiled to bytecode which is then executed by either interpreting (in a [[Java virtual machine]] (JVM)) or compiling (typically with a just-in-time compiler such as [[HotSpot (virtual machine)|HotSpot]], again in a JVM). Moreover, compiling, transcompiling, and interpreting is not strictly limited to only a description of the compiler artifact (binary executable or IL assembly).

Note that languagesa arelanguage is not strictly ''interpreted'' languages or ''compiled'' languages. Rather, implementationsan ofexecution languagemodel behaviorinvolves usea interpretingcompiler or compilingan interpreter and the same language might be used with different execution models. For example, [[ALGOL 60]] and [[Fortran]] have both been interpreted (even though they were more typically compiled). Similarly, Java shows the difficulty of trying to apply these labels to languages, rather than to implementations;. Java is compiled to bytecode which is then executed by either interpreting (in a [[Java virtual machine]] (JVM)) or compilingJIT (typically with a just-in-time compiler such as [[HotSpot (virtual machine)|HotSpot]], again in a JVM). Moreover, compiling, transcompiling, and interpreting is not strictly limited to only a description of the compiler artifact (binary executable or IL assembly)compiled.

=== High-level language computer architecture ===

Alternatively, it is possible for a high-level language to be directly implemented by a computer – the computer directly executes the HLL code. This is known as a ''[[high-level language computer architecture]]'' – the [[computer architecture]] itself is designed to be targeted by a specific high-level language. The [[Burroughs large systems]] were target machines for [[ALGOL 60]], for example.<ref>{{Citation|last=Chu|first=Yaohan|chapter=Concepts of High-Level Language Computer Architecture|date=1975|pages=1–14|publisher=Elsevier|isbn=9780121741501|doi=10.1016/b978-0-12-174150-1.50007-0|title=High-Level Language Computer Architecture}}</ref>

== See also ==