Editing High-level programming language

{{Short description|Programming language that abstracts details of computing hardware}}
{{Use dmy dates|date=May 2023}}
{{Use American English|date=January 2019}}

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>

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>

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.

== Features ==
"High-level language" refers to the higher level of abstraction from [[machine language]]. Rather than dealing with registers, memory addresses, and call stacks, high-level languages deal with variables, arrays, [[object (computer science)|object]]s, complex arithmetic or [[Boolean expression|Boolean expressions]], subroutines and functions, loops, [[Thread (computer science)|thread]]s, locks, and other abstract computer science concepts, with a focus on [[usability]] over optimal program efficiency. 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. 
 |year=2006 
 |url=http://lispnyc.org/meeting-assets/2007-02-13_pinku/SuranaThesis.pdf
 |access-date=2008-03-17 
 |url-status=live
 |archive-url=https://web.archive.org/web/20150217154926/http://lispnyc.org/meeting-assets/2007-02-13_pinku/SuranaThesis.pdf 
 |archive-date=2015-02-17 
}}</ref><ref>{{cite web
  | first = Argyn
  | last = Kuketayev
  | website = Application Development Trends
  | title = The Data Abstraction Penalty (DAP) Benchmark for Small Objects in Java.
  | url = http://www.adtmag.com/joop/article.aspx?id=4597
  | access-date = 2008-03-17
  | archive-url = https://web.archive.org/web/20090111091710/http://www.adtmag.com/joop/article.aspx?id=4597
  | archive-date = 2009-01-11
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  }}</ref><ref>{{Cite book
  | last1 = Chatzigeorgiou
  | last2 = Stephanides
  | editor-last = Blieberger
  | editor2-last = Strohmeier
  | contribution = Evaluating Performance and Power Of Object-Oriented Vs. Procedural Programming Languages
  | title = Proceedings - 7th International Conference on Reliable Software Technologies - Ada-Europe'2002
  | year = 2002
  | pages = 367
  | publisher = Springer
  }}</ref> For this reason, code which 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. In many cases, critical portions of a program mostly in a high-level language can be hand-coded in [[assembly language]], leading to a much faster, more efficient, or simply reliably functioning [[Program optimisation|optimised program]].

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
  | title = High-level languages for small devices: a case study
  | url = http://www.clip.dia.fi.upm.es/papers/carro06:stream_interpreter_cases.pdf
  | year = 2006
  | publisher = ACM
  }}</ref>
High-level languages are designed independent of a specific computing [[Computer architecture|system architecture]]. This facilitates executing a program written in such a language on any computing system with compatible support for the Interpreted or [[Just-in-time compilation|JIT]] program. High-level languages can be improved as their designers develop improvements. In other cases, new high-level languages evolve from one or more others with the goal of aggregating the most popular constructs with new or improved features. An example of this is [[Scala (programming language)|Scala]] which maintains backward compatibility with [[Java (programming language)|Java]], meaning that programs and libraries written in Java will continue to be usable even if a programming shop switches to Scala; this makes the transition easier and the lifespan of such high-level coding indefinite. 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 ==
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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. 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>

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>

== Execution modes ==
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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: 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]].
:; 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]].

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).

=== 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 ==
{{Portal|Computer programming}}
* [[Generational list of programming languages]]
* [[Categorical list of programming languages]]
* [[Very high-level programming language]]s
* [[Low-level programming language]]s
* [[High-level assembler]]
* [[Abstraction (computer science)]]
{{Clear}}

== References ==
{{Reflist}}

== External links ==
* http://c2.com/cgi/wiki?HighLevelLanguage - The [[WikiWikiWeb]]'s article on high-level programming languages

{{Types of programming languages}}
{{Authority control}}

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[[Category:High-level programming languages| ]]
[[Category:Programming language classification]]