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A programming language is a system of notation for writing
computer programs A computer program is a sequence or set of instructions in a programming language for a computer to execute. Computer programs are one component of software, which also includes documentation and other intangible components. A computer program ...
. Most programming languages are text-based
formal language In logic, mathematics, computer science, and linguistics, a formal language consists of words whose letters are taken from an alphabet and are well-formed according to a specific set of rules. The alphabet of a formal language consists of sy ...
s, but they may also be
graphical Graphics () are visual images or designs on some surface, such as a wall, canvas, screen, paper, or stone, to inform, illustrate, or entertain. In contemporary usage, it includes a pictorial representation of data, as in design and manufacture ...
. They are a kind of
computer language A computer language is a formal language used to communicate with a computer. Types of computer languages include: * Construction language – all forms of communication by which a human can specify an executable problem solution to a comput ...
. The description of a programming language is usually split into the two components of syntax (form) and
semantics Semantics (from grc, σημαντικός ''sēmantikós'', "significant") is the study of reference, meaning, or truth. The term can be used to refer to subfields of several distinct disciplines, including philosophy, linguistics and comp ...
(meaning), which are usually defined by a
formal language In logic, mathematics, computer science, and linguistics, a formal language consists of words whose letters are taken from an alphabet and are well-formed according to a specific set of rules. The alphabet of a formal language consists of sy ...
. Some languages are defined by a specification document (for example, the C programming language is specified by an
ISO ISO is the most common abbreviation for the International Organization for Standardization. ISO or Iso may also refer to: Business and finance * Iso (supermarket), a chain of Danish supermarkets incorporated into the SuperBest chain in 2007 * Iso ...
Standard) while other languages (such as
Perl Perl is a family of two high-level, general-purpose, interpreted, dynamic programming languages. "Perl" refers to Perl 5, but from 2000 to 2019 it also referred to its redesigned "sister language", Perl 6, before the latter's name was offic ...
) have a dominant
implementation Implementation is the realization of an application, or execution of a plan, idea, model, design, specification, standard, algorithm, or policy. Industry-specific definitions Computer science In computer science, an implementation is a real ...
that is treated as a
reference Reference is a relationship between objects in which one object designates, or acts as a means by which to connect to or link to, another object. The first object in this relation is said to ''refer to'' the second object. It is called a '' name'' ...
. Some languages have both, with the basic language defined by a standard and extensions taken from the dominant implementation being common. Programming language theory is the subfield of
computer science Computer science is the study of computation, automation, and information. Computer science spans theoretical disciplines (such as algorithms, theory of computation, information theory, and automation) to practical disciplines (includi ...
that studies the design, implementation, analysis, characterization, and classification of programming languages.


Definitions

There are many considerations when defining what constitutes a programming language.


Computer languages vs programming languages

The term ''
computer language A computer language is a formal language used to communicate with a computer. Types of computer languages include: * Construction language – all forms of communication by which a human can specify an executable problem solution to a comput ...
'' is sometimes used interchangeably with programming language. However, the usage of both terms varies among authors, including the exact scope of each. One usage describes programming languages as a subset of computer languages. Similarly, languages used in computing that have a different goal than expressing computer programs are generically designated computer languages. For instance, markup languages are sometimes referred to as computer languages to emphasize that they are not meant to be used for programming. One way of classifying computer languages is by the computations they are capable of expressing, as described by the
theory of computation In theoretical computer science and mathematics, the theory of computation is the branch that deals with what problems can be solved on a model of computation, using an algorithm, how algorithmic efficiency, efficiently they can be solved or t ...
. The majority of practical programming languages are
Turing complete Alan Mathison Turing (; 23 June 1912 – 7 June 1954) was an English mathematician, computer scientist, logician, cryptanalyst, philosopher, and theoretical biologist. Turing was highly influential in the development of theoretical co ...
, and all Turing complete languages can implement the same set of
algorithm In mathematics and computer science, an algorithm () is a finite sequence of rigorous instructions, typically used to solve a class of specific problems or to perform a computation. Algorithms are used as specifications for performing ...
s. ANSI/ISO SQL-92 and Charity are examples of languages that are not Turing complete, yet are often called programming languages., "Charity is a categorical programming language...", "All Charity computations terminate." However, some authors restrict the term "programming language" to Turing complete languages.In mathematical terms, this means the programming language is
Turing-complete In computability theory, a system of data-manipulation rules (such as a computer's instruction set, a programming language, or a cellular automaton) is said to be Turing-complete or computationally universal if it can be used to simulate any ...
Another usage regards programming languages as theoretical constructs for programming
abstract machine An abstract machine is a computer science theoretical model that allows for a detailed and precise analysis of how a computer system functions. It is analogous to a mathematical function in that it receives inputs and produces outputs based on pr ...
s and computer languages as the subset thereof that runs on physical computers, which have finite hardware resources.
John C. Reynolds John Charles Reynolds (June 1, 1935 – April 28, 2013) was an American computer scientist. Education and affiliations John Reynolds studied at Purdue University and then earned a Doctor of Philosophy (Ph.D.) in theoretical physics from Harvard U ...
emphasizes that
formal specification In computer science, formal specifications are mathematically based techniques whose purpose are to help with the implementation of systems and software. They are used to describe a system, to analyze its behavior, and to aid in its design by verif ...
languages are just as much programming languages as are the languages intended for execution. He also argues that textual and even graphical input formats that affect the behavior of a computer are programming languages, despite the fact they are commonly not Turing-complete, and remarks that ignorance of programming language concepts is the reason for many flaws in input formats.


Domain and target

In most practical contexts, a programming language involves a computer; consequently, programming languages are usually defined and studied this way. Programming languages differ from
natural languages In neuropsychology, linguistics, and philosophy of language, a natural language or ordinary language is any language that has evolved naturally in humans through use and repetition without conscious planning or premeditation. Natural languages ...
in that natural languages are only used for interaction between people, while programming languages also allow humans to communicate instructions to machines. The domain of the language is also worth consideration.
Markup languages Markup language refers to a text-encoding system consisting of a set of symbols inserted in a text document to control its structure, formatting, or the relationship between its parts. Markup is often used to control the display of the document ...
like
XML Extensible Markup Language (XML) is a markup language and file format for storing, transmitting, and reconstructing arbitrary data. It defines a set of rules for encoding documents in a format that is both human-readable and machine-readable ...
,
HTML The HyperText Markup Language or HTML is the standard markup language for documents designed to be displayed in a web browser. It can be assisted by technologies such as Cascading Style Sheets (CSS) and scripting languages such as JavaSc ...
, or
troff troff (), short for "typesetter roff", is the major component of a document processing system developed by Bell Labs for the Unix operating system. troff and the related nroff were both developed from the original roff. While nroff was inte ...
, which define
structured data A data model is an abstract model that organizes elements of data and standardizes how they relate to one another and to the properties of real-world entities. For instance, a data model may specify that the data element representing a car be c ...
, are not usually considered programming languages. Programming languages may, however, share the syntax with markup languages if computational semantics is defined. XSLT, for example, is a Turing complete language entirely using XML syntax. Moreover,
LaTeX Latex is an emulsion (stable dispersion) of polymer microparticles in water. Latexes are found in nature, but synthetic latexes are common as well. In nature, latex is found as a milky fluid found in 10% of all flowering plants (angiosperms ...
, which is mostly used for structuring documents, also contains a Turing complete subset.


Abstractions

Programming languages usually contain abstractions for defining and manipulating data structures or controlling the flow of execution. The practical necessity that a programming language support adequate abstractions is expressed by the abstraction principle. This principle is sometimes formulated as a recommendation to the programmer to make proper use of such abstractions.


History


Early developments

Very early computers, such as
Colossus Colossus, Colossos, or the plural Colossi or Colossuses, may refer to: Statues * Any exceptionally large statue ** List of tallest statues ** :Colossal statues * ''Colossus of Barletta'', a bronze statue of an unidentified Roman emperor * ''Col ...
, were programmed without the help of a
stored program A stored-program computer is a computer that stores program instructions in electronically or optically accessible memory. This contrasts with systems that stored the program instructions with plugboards or similar mechanisms. The definition ...
, by modifying their circuitry or setting banks of physical controls. Slightly later, programs could be written in
machine language In computer programming, machine code is any low-level programming language, consisting of machine language instructions, which are used to control a computer's central processing unit (CPU). Each instruction causes the CPU to perform a very ...
, where the programmer writes each instruction in a numeric form the hardware can execute directly. For example, the instruction to add the value in two memory locations might consist of 3 numbers: an "opcode" that selects the "add" operation, and two memory locations. The programs, in decimal or binary form, were read in from
punched card A punched card (also punch card or punched-card) is a piece of stiff paper that holds digital data represented by the presence or absence of holes in predefined positions. Punched cards were once common in data processing applications or to di ...
s, paper tape, magnetic tape or toggled in on switches on the
front panel A front panel was used on early electronic computers to display and allow the alteration of the state of the machine's internal registers and memory. The front panel usually consisted of arrays of indicator lamps, digit and symbol displays, t ...
of the computer. Machine languages were later termed '' first-generation programming languages'' (1GL). The next step was the development of the so-called ''
second-generation programming language The label of second-generation programming language (2GL) is a generational way to categorize assembly languages. The term was coined to provide a distinction from higher level machine independent third-generation programming languages (3GLs) (su ...
s'' (2GL) or assembly languages, which were still closely tied to the instruction set architecture of the specific computer. These served to make the program much more human-readable and relieved the programmer of tedious and error-prone address calculations. The first ''
high-level programming language In computer science, a high-level programming language is a programming language with strong abstraction from the details of the computer. In contrast to low-level programming languages, it may use natural language ''elements'', be easier to us ...
s'', or ''
third-generation programming language A third-generation programming language (3GL) is a high-level computer programming language that tends to be more machine-independent and programmer-friendly than the machine code of the first-generation and assembly languages of the second-gene ...
s'' (3GL), were written in the 1950s. An early high-level programming language to be designed for a computer was
Plankalkül Plankalkül () is a programming language designed for engineering purposes by Konrad Zuse between 1942 and 1945. It was the first high-level programming language to be designed for a computer. ''Kalkül'' is the German term for a formal system ...
, developed for the German Z3 by
Konrad Zuse Konrad Ernst Otto Zuse (; 22 June 1910 – 18 December 1995) was a German civil engineer, pioneering computer scientist, inventor and businessman. His greatest achievement was the world's first programmable computer; the functional program ...
between 1943 and 1945. However, it was not implemented until 1998 and 2000.
John Mauchly John William Mauchly (August 30, 1907 – January 8, 1980) was an American physicist who, along with J. Presper Eckert, designed ENIAC, the first general-purpose electronic digital computer, as well as EDVAC, BINAC and UNIVAC I, the first ...
's
Short Code codes, or short numbers, are short digit sequences, significantly shorter than telephone numbers, that are used to address messages in the Multimedia Messaging System (MMS) and short message service (SMS) systems of mobile network operators ...
, proposed in 1949, was one of the first high-level languages ever developed for an
electronic computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital electronic computers can perform generic sets of operations known as programs. These program ...
.Sebesta, W.S Concepts of Programming languages. 2006; M6 14:18 pp.44. Unlike
machine code In computer programming, machine code is any low-level programming language, consisting of machine language instructions, which are used to control a computer's central processing unit (CPU). Each instruction causes the CPU to perform a ve ...
, Short Code statements represented mathematical expressions in an understandable form. However, the program had to be translated into machine code every time it ran, making the process much slower than running the equivalent machine code. At the
University of Manchester , mottoeng = Knowledge, Wisdom, Humanity , established = 2004 – University of Manchester Predecessor institutions: 1956 – UMIST (as university college; university 1994) 1904 – Victoria University of Manchester 1880 – Victoria Univ ...
,
Alick Glennie Alick Edwards Glennie (1925–2003) was a British computer scientist, most famous for having developed Autocode, which many people regard as the first ever computer compiler.Knuth, Donald E.; Pardo, Luis Trabb, "Early development of programming ...
developed
Autocode Autocode is the name of a family of "simplified coding systems", later called programming languages, devised in the 1950s and 1960s for a series of digital computers at the Universities of Manchester, Cambridge and London. Autocode was a generic ...
in the early 1950s. As a
programming language A programming language is a system of notation for writing computer programs. Most programming languages are text-based formal languages, but they may also be graphical. They are a kind of computer language. The description of a programming ...
, it used a
compiler In computing, a compiler is a computer program that translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily used for programs tha ...
to automatically convert the language into machine code. The first code and compiler was developed in 1952 for the
Mark 1 Mark 1 is the first chapter of the Gospel of Mark in the New Testament of the Christian Bible. Text The original text was written in Koine Greek. This chapter is divided into 45 verses. Textual witnesses Some early manuscripts conta ...
computer at the University of Manchester and is considered to be the first
compiled In computing, a compiler is a computer program that translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily used for programs that ...
high-level programming language. The second auto code was developed for the Mark 1 by R. A. Brooker in 1954 and was called the "Mark 1 Autocode". Brooker also developed an auto code for the
Ferranti Mercury The Mercury was an early commercial computer from the mid-1950s built by Ferranti. It was the successor to the Ferranti Mark 1, adding a floating point unit for improved performance, and increased reliability by replacing the Williams tube memory w ...
in the 1950s in conjunction with the University of Manchester. The version for the
EDSAC 2 EDSAC 2 was an early computer (operational in 1958), the successor to the Electronic Delay Storage Automatic Calculator (EDSAC). It was the first computer to have a microprogrammed control unit and a bit-slice hardware architecture. First cal ...
was devised by D. F. Hartley of
University of Cambridge Mathematical Laboratory The Department of Computer Science and Technology, formerly the Computer Laboratory, is the computer science department of the University of Cambridge. it employed 35 academic staff, 25 support staff, 35 affiliated research staff, and about 15 ...
in 1961. Known as EDSAC 2 Autocode, it was a straight development from Mercury Autocode adapted for local circumstances and was noted for its object code optimization and source-language diagnostics which were advanced for the time. A contemporary but separate thread of development,
Atlas Autocode Atlas Autocode (AA)Original scans)) is a programming language developed around 1965 at the University of Manchester. A variant of the language ALGOL, it was developed by Tony Brooker and Derrick Morris for the Atlas computer. The AA compiler was ...
was developed for the University of Manchester Atlas 1 machine. In 1954, FORTRAN was invented at IBM by
John Backus John Warner Backus (December 3, 1924 – March 17, 2007) was an American computer scientist. He directed the team that invented and implemented FORTRAN, the first widely used high-level programming language, and was the inventor of the Backu ...
. It was the first widely used high-level general-purpose programming language to have a functional implementation, as opposed to just a design on paper. It is still a popular language for
high-performance computing High-performance computing (HPC) uses supercomputers and computer clusters to solve advanced computation problems. Overview HPC integrates systems administration (including network and security knowledge) and parallel programming into a mult ...
and is used for programs that benchmark and rank the world's fastest supercomputers. Another early programming language was devised by
Grace Hopper Grace Brewster Hopper (; December 9, 1906 – January 1, 1992) was an American computer scientist, mathematician, and United States Navy rear admiral. One of the first programmers of the Harvard Mark I computer, she was a pioneer of compu ...
in the US, called
FLOW-MATIC FLOW-MATIC, originally known as B-0 (Business Language version 0), was the first English-like data processing language. It was developed for the UNIVAC I at Remington Rand under Grace Hopper from 1955 to 1959, and helped shape the development of ...
. It was developed for the
UNIVAC I The UNIVAC I (Universal Automatic Computer I) was the first general-purpose electronic digital computer design for business application produced in the United States. It was designed principally by J. Presper Eckert and John Mauchly, the inven ...
at
Remington Rand Remington Rand was an early American business machine manufacturer, originally a typewriter manufacturer and in a later incarnation the manufacturer of the UNIVAC line of mainframe computers. Formed in 1927 following a merger, Remington Rand w ...
during the period from 1955 until 1959. Hopper found that business data processing customers were uncomfortable with mathematical notation, and in early 1955, she and her team wrote a specification for an
English English usually refers to: * English language * English people English may also refer to: Peoples, culture, and language * ''English'', an adjective for something of, from, or related to England ** English national ide ...
programming language and implemented a prototype. The FLOW-MATIC compiler became publicly available in early 1958 and was substantially complete in 1959. FLOW-MATIC was a major influence in the design of COBOL, since only it and its direct descendant
AIMACO AIMACO is an acronym for AIr MAterial COmpiler. It began around 1959 as the definition of a high level programming language influenced by the FLOW-MATIC language, developed by UNIVAC, and the COMTRAN (COMmercial TRANslator) programming language, ...
were in actual use at the time.


Refinement

The increased use of high-level languages introduced a requirement for ''
low-level programming language A low-level programming language is a programming language that provides little or no Abstraction (computer science), abstraction from a computer's instruction set architecture—commands or functions in the language map that are structurally sim ...
s'' or ''
system programming language A system programming language is a programming language used for system programming; such languages are designed for writing system software, which usually requires different development approaches when compared with application software. Edsger W ...
s''. These languages, to varying degrees, provide facilities between assembly languages and high-level languages. They can be used to perform tasks that require direct access to hardware facilities but still provide higher-level control structures and error-checking. The period from the 1960s to the late 1970s brought the development of the major language paradigms now in use: * APL introduced ''
array programming In computer science, array programming refers to solutions which allow the application of operations to an entire set of values at once. Such solutions are commonly used in computational science, scientific and engineering settings. Modern progr ...
'' and influenced
functional programming In computer science, functional programming is a programming paradigm where programs are constructed by applying and composing functions. It is a declarative programming paradigm in which function definitions are trees of expressions that ...
. *
ALGOL ALGOL (; short for "Algorithmic Language") is a family of imperative computer programming languages originally developed in 1958. ALGOL heavily influenced many other languages and was the standard method for algorithm description used by the ...
refined both ''structured procedural programming'' and the discipline of
language specification In computer programming, a programming language specification (or standard or definition) is a documentation artifact that defines a programming language so that users and implementors can agree on what programs in that language mean. Specifica ...
; the "Revised Report on the Algorithmic Language ALGOL 60" became a model for how later language specifications were written. * Lisp, implemented in 1958, was the first dynamically typed ''
functional programming In computer science, functional programming is a programming paradigm where programs are constructed by applying and composing functions. It is a declarative programming paradigm in which function definitions are trees of expressions that ...
'' language. * In the 1960s, Simula was the first language designed to support ''
object-oriented programming Object-oriented programming (OOP) is a programming paradigm based on the concept of "objects", which can contain data and code. The data is in the form of fields (often known as attributes or ''properties''), and the code is in the form of ...
''; in the mid-1970s, Smalltalk followed with the first "purely" object-oriented language. * C was developed between 1969 and 1973 as a system programming language for the
Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, an ...
operating system and remains popular. *
Prolog Prolog is a logic programming language associated with artificial intelligence and computational linguistics. Prolog has its roots in first-order logic, a formal logic, and unlike many other programming languages, Prolog is intended primarily ...
, designed in 1972, was the first ''
logic programming Logic programming is a programming paradigm which is largely based on formal logic. Any program written in a logic programming language is a set of sentences in logical form, expressing facts and rules about some problem domain. Major logic pro ...
'' language. * In 1978, ML built a polymorphic type system on top of Lisp, pioneering '' statically typed
functional programming In computer science, functional programming is a programming paradigm where programs are constructed by applying and composing functions. It is a declarative programming paradigm in which function definitions are trees of expressions that ...
'' languages. Each of these languages spawned descendants, and most modern programming languages count at least one of them in their ancestry. The 1960s and 1970s also saw considerable debate over the merits of '' structured programming'', and whether programming languages should be designed to support it.
Edsger Dijkstra Edsger Wybe Dijkstra ( ; ; 11 May 1930 – 6 August 2002) was a Dutch computer scientist, programmer, software engineer, systems scientist, and science essayist. He received the 1972 Turing Award for fundamental contributions to developing progra ...
, in a famous 1968 letter published in the
Communications of the ACM ''Communications of the ACM'' is the monthly journal of the Association for Computing Machinery (ACM). It was established in 1958, with Saul Rosen as its first managing editor. It is sent to all ACM members. Articles are intended for readers with ...
, argued that Goto statements should be eliminated from all "higher level" programming languages.


Consolidation and growth

The 1980s were years of relative consolidation.
C++ C++ (pronounced "C plus plus") is a high-level general-purpose programming language created by Danish computer scientist Bjarne Stroustrup as an extension of the C programming language, or "C with Classes". The language has expanded significan ...
combined object-oriented and systems programming. The United States government standardized
Ada Ada may refer to: Places Africa * Ada Foah, a town in Ghana * Ada (Ghana parliament constituency) * Ada, Osun, a town in Nigeria Asia * Ada, Urmia, a village in West Azerbaijan Province, Iran * Ada, Karaman, a village in Karaman Province, ...
, a systems programming language derived from Pascal and intended for use by defense contractors. In Japan and elsewhere, vast sums were spent investigating the so-called "fifth-generation" languages that incorporated logic programming constructs. The functional languages community moved to standardize ML and Lisp. Rather than inventing new paradigms, all of these movements elaborated upon the ideas invented in the previous decades. One important trend in language design for programming large-scale systems during the 1980s was an increased focus on the use of ''modules'' or large-scale organizational units of code. Modula-2, Ada, and ML all developed notable module systems in the 1980s, which were often wedded to
generic programming Generic programming is a style of computer programming in which algorithms are written in terms of types ''to-be-specified-later'' that are then ''instantiated'' when needed for specific types provided as parameters. This approach, pioneered b ...
constructs. The rapid growth of the
Internet The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, pub ...
in the mid-1990s created opportunities for new languages.
Perl Perl is a family of two high-level, general-purpose, interpreted, dynamic programming languages. "Perl" refers to Perl 5, but from 2000 to 2019 it also referred to its redesigned "sister language", Perl 6, before the latter's name was offic ...
, originally a Unix scripting tool first released in 1987, became common in dynamic
website A website (also written as a web site) is a collection of web pages and related content that is identified by a common domain name and published on at least one web server. Examples of notable websites are Google, Facebook, Amazon, and Wi ...
s.
Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's mos ...
came to be used for server-side programming, and bytecode virtual machines became popular again in commercial settings with their promise of "
Write once, run anywhere Write once, run anywhere (WORA), or sometimes Write once, run everywhere (WORE), was a 1995 slogan created by Sun Microsystems to illustrate the cross-platform benefits of the Java language. Ideally, this meant that a Java program could be develope ...
" (
UCSD Pascal UCSD Pascal is a Pascal programming language system that runs on the UCSD p-System, a portable, highly machine-independent operating system. UCSD Pascal was first released in 1977. It was developed at the University of California, San Diego (U ...
had been popular for a time in the early 1980s). These developments were not fundamentally novel; rather, they were refinements of many existing languages and paradigms (although their syntax was often based on the C family of programming languages). Programming language evolution continues, in both industry and research. Current directions include security and reliability verification, new kinds of modularity (
mixin In object-oriented programming languages, a mixin (or mix-in) is a class that contains methods for use by other classes without having to be the parent class of those other classes. How those other classes gain access to the mixin's methods depen ...
s, delegates, aspects), and database integration such as Microsoft's
LINQ Language Integrated Query (LINQ, pronounced "link") is a Microsoft .NET Framework component that adds native data querying capabilities to .NET languages, originally released as a major part of .NET Framework 3.5 in 2007. LINQ extends the langu ...
. ''
Fourth-generation programming language A fourth-generation programming language (4GL) is any computer programming language that belongs to a class of languages envisioned as an advancement upon third-generation programming languages (3GL). Each of the programming language generations a ...
s'' (4GL) are computer programming languages that aim to provide a higher level of abstraction of the internal computer hardware details than 3GLs. '' Fifth-generation programming languages'' (5GL) are programming languages based on solving problems using constraints given to the program, rather than using an
algorithm In mathematics and computer science, an algorithm () is a finite sequence of rigorous instructions, typically used to solve a class of specific problems or to perform a computation. Algorithms are used as specifications for performing ...
written by a programmer.


Elements

All programming languages have some primitive building blocks for the description of data and the processes or transformations applied to them (like the addition of two numbers or the selection of an item from a collection). These primitives are defined by syntactic and semantic rules which describe their structure and meaning respectively.


Syntax

A programming language's surface form is known as its syntax. Most programming languages are purely textual; they use sequences of text including words, numbers, and punctuation, much like written natural languages. On the other hand, some programming languages are more
graphical Graphics () are visual images or designs on some surface, such as a wall, canvas, screen, paper, or stone, to inform, illustrate, or entertain. In contemporary usage, it includes a pictorial representation of data, as in design and manufacture ...
in nature, using visual relationships between symbols to specify a program. The syntax of a language describes the possible combinations of symbols that form a syntactically correct program. The meaning given to a combination of symbols is handled by semantics (either formal or hard-coded in a
reference implementation In the software development process, a reference implementation (or, less frequently, sample implementation or model implementation) is a program that implements all requirements from a corresponding specification. The reference implementation o ...
). Since most languages are textual, this article discusses textual syntax. The programming language syntax is usually defined using a combination of
regular expression A regular expression (shortened as regex or regexp; sometimes referred to as rational expression) is a sequence of characters that specifies a search pattern in text. Usually such patterns are used by string-searching algorithms for "find" ...
s (for
lexical Lexical may refer to: Linguistics * Lexical corpus or lexis, a complete set of all words in a language * Lexical item, a basic unit of lexicographical classification * Lexicon, the vocabulary of a person, language, or branch of knowledge * Lex ...
structure) and Backus–Naur form (for grammatical structure). Below is a simple grammar, based on Lisp: expression ::= atom , list atom ::= number , symbol number ::= - 0'-'9' symbol ::= A'-'Z''a'-'z'* list ::= '(' expression* ')' This grammar specifies the following: * an ''expression'' is either an ''atom'' or a ''list''; * an ''atom'' is either a ''number'' or a ''symbol''; * a ''number'' is an unbroken sequence of one or more decimal digits, optionally preceded by a plus or minus sign; * a ''symbol'' is a letter followed by zero or more of any characters (excluding whitespace); and * a ''list'' is a matched pair of parentheses, with zero or more ''expressions'' inside it. The following are examples of well-formed token sequences in this grammar: 12345, () and (a b c232 (1)). Not all syntactically correct programs are semantically correct. Many syntactically correct programs are nonetheless ill-formed, per the language's rules; and may (depending on the language specification and the soundness of the implementation) result in an error on translation or execution. In some cases, such programs may exhibit
undefined behavior In computer programming, undefined behavior (UB) is the result of executing a program whose behavior is prescribed to be unpredictable, in the language specification to which the computer code adheres. This is different from unspecified behavior ...
. Even when a program is well-defined within a language, it may still have a meaning that is not intended by the person who wrote it. Using natural language as an example, it may not be possible to assign a meaning to a grammatically correct sentence or the sentence may be false: * " Colorless green ideas sleep furiously." is grammatically well-formed but has no generally accepted meaning. * "John is a married bachelor." is grammatically well-formed but expresses a meaning that cannot be true. The following
C language C (''pronounced like the letter c'') is a general-purpose computer programming language. It was created in the 1970s by Dennis Ritchie, and remains very widely used and influential. By design, C's features cleanly reflect the capabilities o ...
fragment is syntactically correct, but performs operations that are not semantically defined (the operation *p >> 4 has no meaning for a value having a complex type and p->im is not defined because the value of p is the null pointer): complex *p = NULL; complex abs_p = sqrt(*p >> 4 + p->im); If the
type declaration In computer programming, a declaration is a language construct specifying identifier properties: it declares a word's (identifier's) meaning."A declaration specifies the interpretation and attributes of a set of identifiers. A ''definition'' of a ...
on the first line were omitted, the program would trigger an error on the undefined variable p during compilation. However, the program would still be syntactically correct since type declarations provide only semantic information. The grammar needed to specify a programming language can be classified by its position in the
Chomsky hierarchy In formal language theory, computer science and linguistics, the Chomsky hierarchy (also referred to as the Chomsky–Schützenberger hierarchy) is a containment hierarchy of classes of formal grammars. This hierarchy of grammars was described by ...
. The syntax of most programming languages can be specified using a Type-2 grammar, i.e., they are context-free grammars. Some languages, including Perl and Lisp, contain constructs that allow execution during the parsing phase. Languages that have constructs that allow the programmer to alter the behavior of the parser make syntax analysis an
undecidable problem In computability theory and computational complexity theory, an undecidable problem is a decision problem for which it is proved to be impossible to construct an algorithm that always leads to a correct yes-or-no answer. The halting problem is an ...
, and generally blur the distinction between parsing and execution. In contrast to Lisp's macro system and Perl's BEGIN blocks, which may contain general computations, C macros are merely string replacements and do not require code execution.


Semantics

The term ''semantics'' refers to the meaning of languages, as opposed to their form ( syntax).


Static semantics

Static semantics defines restrictions on the structure of valid texts that are hard or impossible to express in standard syntactic formalisms. For compiled languages, static semantics essentially include those semantic rules that can be checked at compile time. Examples include checking that every identifier is declared before it is used (in languages that require such declarations) or that the labels on the arms of a
case statement In computer programming languages, a switch statement is a type of selection control mechanism used to allow the value of a variable (programming), variable or expression to change the control flow of program execution via search and map. Switch ...
are distinct. Many important restrictions of this type, like checking that identifiers are used in the appropriate context (e.g. not adding an integer to a function name), or that subroutine calls have the appropriate number and type of arguments, can be enforced by defining them as rules in a
logic Logic is the study of correct reasoning. It includes both formal and informal logic. Formal logic is the science of deductively valid inferences or of logical truths. It is a formal science investigating how conclusions follow from premise ...
called a
type system In computer programming, a type system is a logical system comprising a set of rules that assigns a property called a type to every "term" (a word, phrase, or other set of symbols). Usually the terms are various constructs of a computer progr ...
. Other forms of static analyses like
data flow analysis In the pursuit of knowledge, data (; ) is a collection of discrete values that convey information, describing quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpreted. ...
may also be part of static semantics. Newer programming languages like
Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's mos ...
and C# have definite assignment analysis, a form of data flow analysis, as part of their static semantics.


Dynamic semantics

Once data has been specified, the machine must be instructed to perform operations on the data. For example, the semantics may define the strategy by which expressions are evaluated to values, or the manner in which
control structures In computer science, control flow (or flow of control) is the order in which individual statements, instructions or function calls of an imperative program are executed or evaluated. The emphasis on explicit control flow distinguishes an ''imp ...
conditionally execute
statements Statement or statements may refer to: Common uses *Statement (computer science), the smallest standalone element of an imperative programming language *Statement (logic), declarative sentence that is either true or false *Statement, a declarative ...
. The ''dynamic semantics'' (also known as ''execution semantics'') of a language defines how and when the various constructs of a language should produce a program behavior. There are many ways of defining execution semantics. Natural language is often used to specify the execution semantics of languages commonly used in practice. A significant amount of academic research went into
formal semantics of programming languages In programming language theory, semantics is the rigorous mathematical study of the meaning of programming languages. Semantics assigns computational meaning to valid strings in a programming language syntax. Semantics describes the processes ...
, which allows execution semantics to be specified in a formal manner. Results from this field of research have seen limited application to programming language design and implementation outside academia.


Type system

A type system defines how a programming language classifies values and expressions into ''types'', how it can manipulate those types and how they interact. The goal of a type system is to verify and usually enforce a certain level of correctness in programs written in that language by detecting certain incorrect operations. Any decidable type system involves a trade-off: while it rejects many incorrect programs, it can also prohibit some correct, albeit unusual programs. In order to bypass this downside, a number of languages have ''type loopholes'', usually unchecked casts that may be used by the programmer to explicitly allow a normally disallowed operation between different types. In most typed languages, the type system is used only to type check programs, but a number of languages, usually functional ones, infer types, relieving the programmer from the need to write type annotations. The formal design and study of type systems is known as ''
type theory In mathematics, logic, and computer science, a type theory is the formal presentation of a specific type system, and in general type theory is the academic study of type systems. Some type theories serve as alternatives to set theory as a fou ...
''.


Typed versus untyped languages

A language is ''typed'' if the specification of every operation defines types of data to which the operation is applicable. For example, the data represented by "this text between the quotes" is a string, and in many programming languages dividing a number by a string has no meaning and will not be executed. The invalid operation may be detected when the program is compiled ("static" type checking) and will be rejected by the compiler with a compilation error message, or it may be detected while the program is running ("dynamic" type checking), resulting in a run-time exception. Many languages allow a function called an exception handler to handle this exception and, for example, always return "-1" as the result. A special case of typed languages are the ''single-typed'' languages. These are often scripting or markup languages, such as REXX or SGML, and have only one data type–—most commonly character strings which are used for both symbolic and numeric data. In contrast, an ''untyped language'', such as most assembly languages, allows any operation to be performed on any data, generally sequences of bits of various lengths. High-level untyped languages include BCPL,
Tcl TCL or Tcl or TCLs may refer to: Business * TCL Technology, a Chinese consumer electronics and appliance company **TCL Electronics, a subsidiary of TCL Technology * Texas Collegiate League, a collegiate baseball league * Trade Centre Limited ...
, and some varieties of
Forth Forth or FORTH may refer to: Arts and entertainment * ''forth'' magazine, an Internet magazine * ''Forth'' (album), by The Verve, 2008 * ''Forth'', a 2011 album by Proto-Kaw * Radio Forth, a group of independent local radio stations in Scotla ...
. In practice, while few languages are considered typed from the
type theory In mathematics, logic, and computer science, a type theory is the formal presentation of a specific type system, and in general type theory is the academic study of type systems. Some type theories serve as alternatives to set theory as a fou ...
(verifying or rejecting all operations), most modern languages offer a degree of typing. Many production languages provide means to bypass or subvert the type system, trading type safety for finer control over the program's execution (see
casting Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a ''casting'', which is ejected ...
).


Static vis-à-vis dynamic typing

In ''
static typing In computer programming, a type system is a logical system comprising a set of rules that assigns a property called a type to every "term" (a word, phrase, or other set of symbols). Usually the terms are various constructs of a computer progra ...
'', all expressions have their types determined prior to when the program is executed, typically at compile-time. For example, 1 and (2+2) are integer expressions; they cannot be passed to a function that expects a string or stored in a variable that is defined to hold dates. Statically typed languages can be either '' manifestly typed'' or '' type-inferred''. In the first case, the programmer must explicitly write types at certain textual positions (for example, at variable declarations). In the second case, the compiler ''infers'' the types of expressions and declarations based on context. Most mainstream statically typed languages, such as
C++ C++ (pronounced "C plus plus") is a high-level general-purpose programming language created by Danish computer scientist Bjarne Stroustrup as an extension of the C programming language, or "C with Classes". The language has expanded significan ...
, C# and
Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's mos ...
, are manifestly typed. Complete type inference has traditionally been associated with less mainstream languages, such as
Haskell Haskell () is a general-purpose, statically-typed, purely functional programming language with type inference and lazy evaluation. Designed for teaching, research and industrial applications, Haskell has pioneered a number of programming lan ...
and ML. However, many manifestly typed languages support partial type inference; for example,
C++ C++ (pronounced "C plus plus") is a high-level general-purpose programming language created by Danish computer scientist Bjarne Stroustrup as an extension of the C programming language, or "C with Classes". The language has expanded significan ...
,
Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's mos ...
, and C# all infer types in certain limited cases. Additionally, some programming languages allow for some types to be automatically converted to other types; for example, an int can be used where the program expects a float. ''
Dynamic typing In computer programming, a type system is a logical system comprising a set of rules that assigns a property called a type to every "term" (a word, phrase, or other set of symbols). Usually the terms are various constructs of a computer progra ...
'', also called ''latent typing'', determines the type-safety of operations at run time; in other words, types are associated with ''run-time values'' rather than ''textual expressions''. As with type-inferred languages, dynamically typed languages do not require the programmer to write explicit type annotations on expressions. Among other things, this may permit a single variable to refer to values of different types at different points in the program execution. However, type errors cannot be automatically detected until a piece of code is actually executed, potentially making debugging more difficult. Lisp, Smalltalk,
Perl Perl is a family of two high-level, general-purpose, interpreted, dynamic programming languages. "Perl" refers to Perl 5, but from 2000 to 2019 it also referred to its redesigned "sister language", Perl 6, before the latter's name was offic ...
,
Python Python may refer to: Snakes * Pythonidae, a family of nonvenomous snakes found in Africa, Asia, and Australia ** ''Python'' (genus), a genus of Pythonidae found in Africa and Asia * Python (mythology), a mythical serpent Computing * Python (pro ...
,
JavaScript JavaScript (), often abbreviated as JS, is a programming language that is one of the core technologies of the World Wide Web, alongside HTML and CSS. As of 2022, 98% of websites use JavaScript on the client side for webpage behavior, of ...
, and
Ruby A ruby is a pinkish red to blood-red colored gemstone, a variety of the mineral corundum ( aluminium oxide). Ruby is one of the most popular traditional jewelry gems and is very durable. Other varieties of gem-quality corundum are called ...
are all examples of dynamically typed languages.


Weak and strong typing

''
Weak typing In computer programming, one of the many ways that programming languages are colloquially classified is whether the language's type system makes it strongly typed or weakly typed (loosely typed). However, there is no precise technical definition o ...
'' allows a value of one type to be treated as another, for example treating a string as a number. This can occasionally be useful, but it can also allow some kinds of program faults to go undetected at
compile time In computer science, compile time (or compile-time) describes the time window during which a computer program is compiled. The term is used as an adjective to describe concepts related to the context of program compilation, as opposed to concep ...
and even at
run time Run(s) or RUN may refer to: Places * Run (island), one of the Banda Islands in Indonesia * Run (stream), a stream in the Dutch province of North Brabant People * Run (rapper), Joseph Simmons, now known as "Reverend Run", from the hip-hop group ...
. '' Strong typing'' prevents these program faults. An attempt to perform an operation on the wrong type of value raises an error. Strongly typed languages are often termed ''type-safe'' or '' safe''. An alternative definition for "weakly typed" refers to languages, such as
Perl Perl is a family of two high-level, general-purpose, interpreted, dynamic programming languages. "Perl" refers to Perl 5, but from 2000 to 2019 it also referred to its redesigned "sister language", Perl 6, before the latter's name was offic ...
and
JavaScript JavaScript (), often abbreviated as JS, is a programming language that is one of the core technologies of the World Wide Web, alongside HTML and CSS. As of 2022, 98% of websites use JavaScript on the client side for webpage behavior, of ...
, which permit a large number of implicit type conversions. In JavaScript, for example, the expression 2 * x implicitly converts x to a number, and this conversion succeeds even if x is null, undefined, an Array, or a string of letters. Such implicit conversions are often useful, but they can mask programming errors. ''Strong'' and ''static'' are now generally considered orthogonal concepts, but usage in the literature differs. Some use the term ''strongly typed'' to mean ''strongly, statically typed'', or, even more confusingly, to mean simply ''statically typed''. Thus C has been called both strongly typed and weakly, statically typed. It may seem odd to some professional programmers that C could be "weakly, statically typed". However, notice that the use of the generic pointer, the void* pointer, does allow casting pointers to other pointers without needing to do an explicit cast. This is extremely similar to somehow casting an array of bytes to any kind of datatype in C without using an explicit cast, such as (int) or (char).


Standard library and run-time system

Most programming languages have an associated core
library A library is a collection of materials, books or media that are accessible for use and not just for display purposes. A library provides physical (hard copies) or digital access (soft copies) materials, and may be a physical location or a vir ...
(sometimes known as the "standard library", especially if it is included as part of the published language standard), which is conventionally made available by all implementations of the language. Core libraries typically include definitions for commonly used algorithms, data structures, and mechanisms for input and output. The line between a language and its core library differs from language to language. In some cases, the language designers may treat the library as a separate entity from the language. However, a language's core library is often treated as part of the language by its users, and some language specifications even require that this library be made available in all implementations. Indeed, some languages are designed so that the meanings of certain syntactic constructs cannot even be described without referring to the core library. For example, in
Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's mos ...
, a string literal is defined as an instance of the java.lang.String class; similarly, in Smalltalk, an anonymous function expression (a "block") constructs an instance of the library's BlockContext class. Conversely,
Scheme A scheme is a systematic plan for the implementation of a certain idea. Scheme or schemer may refer to: Arts and entertainment * ''The Scheme'' (TV series), a BBC Scotland documentary series * The Scheme (band), an English pop band * ''The Schem ...
contains multiple coherent subsets that suffice to construct the rest of the language as library macros, and so the language designers do not even bother to say which portions of the language must be implemented as language constructs, and which must be implemented as parts of a library.


Design and implementation

Programming languages share properties with natural languages related to their purpose as vehicles for communication, having a syntactic form separate from its semantics, and showing ''language families'' of related languages branching one from another.Steven R. Fischer, ''A history of language'', Reaktion Books, 2003, , p. 205 But as artificial constructs, they also differ in fundamental ways from languages that have evolved through usage. A significant difference is that a programming language can be fully described and studied in its entirety since it has a precise and finite definition. By contrast, natural languages have changing meanings given by their users in different communities. While
constructed languages A constructed language (sometimes called a conlang) is a language whose phonology, grammar, and vocabulary, instead of having developed naturally, are consciously devised for some purpose, which may include being devised for a work of fiction. ...
are also artificial languages designed from the ground up with a specific purpose, they lack the precise and complete semantic definition that a programming language has. Many programming languages have been designed from scratch, altered to meet new needs, and combined with other languages. Many have eventually fallen into disuse. Although there have been attempts to design one "universal" programming language that serves all purposes, all of them have failed to be generally accepted as filling this role. The need for diverse programming languages arises from the diversity of contexts in which languages are used: * Programs range from tiny scripts written by individual hobbyists to huge systems written by hundreds of programmers. * Programmers range in expertise from novices who need simplicity above all else to experts who may be comfortable with considerable complexity. * Programs must balance speed, size, and simplicity on systems ranging from microcontrollers to supercomputers. * Programs may be written once and not change for generations, or they may undergo continual modification. * Programmers may simply differ in their tastes: they may be accustomed to discussing problems and expressing them in a particular language. One common trend in the development of programming languages has been to add more ability to solve problems using a higher level of abstraction. The earliest programming languages were tied very closely to the underlying hardware of the computer. As new programming languages have developed, features have been added that let programmers express ideas that are more remote from simple translation into underlying hardware instructions. Because programmers are less tied to the complexity of the computer, their programs can do more computing with less effort from the programmer. This lets them write more functionality per time unit.
Natural language programming Natural-language programming (NLP) is an ontology-assisted way of programming in terms of natural-language sentences, e.g. English. A structured document with Content, sections and subsections for explanations of sentences forms a NLP docume ...
has been proposed as a way to eliminate the need for a specialized language for programming. However, this goal remains distant and its benefits are open to debate. Edsger W. Dijkstra took the position that the use of a formal language is essential to prevent the introduction of meaningless constructs, and dismissed
natural language programming Natural-language programming (NLP) is an ontology-assisted way of programming in terms of natural-language sentences, e.g. English. A structured document with Content, sections and subsections for explanations of sentences forms a NLP docume ...
as "foolish".
Alan Perlis Alan Jay Perlis (April 1, 1922 – February 7, 1990) was an American computer scientist and professor at Purdue University, Carnegie Mellon University and Yale University. He is best known for his pioneering work in programming languages and was t ...
was similarly dismissive of the idea. Hybrid approaches have been taken in Structured English and SQL. A language's designers and users must construct a number of artifacts that govern and enable the practice of programming. The most important of these artifacts are the language ''specification'' and ''implementation''.


Specification

The specification of a programming language is an artifact that the language
users Ancient Egyptian roles * User (ancient Egyptian official), an ancient Egyptian nomarch (governor) of the Eighth Dynasty * Useramen, an ancient Egyptian vizier also called "User" Other uses * User (computing) A user is a person who ...
and the implementors can use to agree upon whether a piece of
source code In computing, source code, or simply code, is any collection of code, with or without comments, written using a human-readable programming language, usually as plain text. The source code of a program is specially designed to facilitate the w ...
is a valid
program Program, programme, programmer, or programming may refer to: Business and management * Program management, the process of managing several related projects * Time management * Program, a part of planning Arts and entertainment Audio * Progra ...
in that language, and if so what its behavior shall be. A programming language specification can take several forms, including the following: * An explicit definition of the syntax, static semantics, and execution semantics of the language. While syntax is commonly specified using a formal grammar, semantic definitions may be written in natural language (e.g., as in the
C language C (''pronounced like the letter c'') is a general-purpose computer programming language. It was created in the 1970s by Dennis Ritchie, and remains very widely used and influential. By design, C's features cleanly reflect the capabilities o ...
), or a formal semantics (e.g., as in Standard ML and
Scheme A scheme is a systematic plan for the implementation of a certain idea. Scheme or schemer may refer to: Arts and entertainment * ''The Scheme'' (TV series), a BBC Scotland documentary series * The Scheme (band), an English pop band * ''The Schem ...
specifications). * A description of the behavior of a
translator Translation is the communication of the meaning of a source-language text by means of an equivalent target-language text. The English language draws a terminological distinction (which does not exist in every language) between ''transl ...
for the language (e.g., the
C++ C++ (pronounced "C plus plus") is a high-level general-purpose programming language created by Danish computer scientist Bjarne Stroustrup as an extension of the C programming language, or "C with Classes". The language has expanded significan ...
and Fortran specifications). The syntax and semantics of the language have to be inferred from this description, which may be written in natural or formal language. * A ''reference'' or ''model'' implementation, sometimes written in the language being specified (e.g.,
Prolog Prolog is a logic programming language associated with artificial intelligence and computational linguistics. Prolog has its roots in first-order logic, a formal logic, and unlike many other programming languages, Prolog is intended primarily ...
or ANSI REXX). The syntax and semantics of the language are explicit in the behavior of the reference implementation.


Implementation

An ''implementation'' of a programming language provides a way to write programs in that language and execute them on one or more configurations of hardware and software. There are, broadly, two approaches to programming language implementation: ''
compilation Compilation may refer to: *In computer programming, the translation of source code into object code by a compiler **Compilation error **Compilation unit *Product bundling, a marketing strategy used to sell multiple products *Compilation thesis M ...
'' and '' interpretation''. It is generally possible to implement a language using either technique. The output of a
compiler In computing, a compiler is a computer program that translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily used for programs tha ...
may be executed by hardware or a program called an interpreter. In some implementations that make use of the interpreter approach, there is no distinct boundary between compiling and interpreting. For instance, some implementations of BASIC compile and then execute the source one line at a time. Programs that are executed directly on the hardware usually run much faster than those that are interpreted in software. One technique for improving the performance of interpreted programs is
just-in-time compilation In computing, just-in-time (JIT) compilation (also dynamic translation or run-time compilations) is a way of executing computer code that involves compilation during execution of a program (at run time) rather than before execution. This may co ...
. Here the
virtual machine In computing, a virtual machine (VM) is the virtualization/ emulation of a computer system. Virtual machines are based on computer architectures and provide functionality of a physical computer. Their implementations may involve specialized h ...
, just before execution, translates the blocks of
bytecode Bytecode (also called portable code or p-code) is a form of instruction set designed for efficient execution by a software interpreter. Unlike human-readable source code, bytecodes are compact numeric codes, constants, and references (norma ...
which are going to be used to machine code, for direct execution on the hardware.


Proprietary languages

Although most of the most commonly used programming languages have fully open specifications and implementations, many programming languages exist only as proprietary programming languages with the implementation available only from a single vendor, which may claim that such a proprietary language is their intellectual property. Proprietary programming languages are commonly
domain specific language A domain-specific language (DSL) is a computer language specialized to a particular application domain. This is in contrast to a general-purpose language (GPL), which is broadly applicable across domains. There are a wide variety of DSLs, ranging ...
s or internal
scripting language A scripting language or script language is a programming language that is used to manipulate, customize, and automate the facilities of an existing system. Scripting languages are usually interpreted at runtime rather than compiled. A scripting ...
s for a single product; some proprietary languages are used only internally within a vendor, while others are available to external users. Some programming languages exist on the border between proprietary and open; for example, Oracle Corporation asserts proprietary rights to some aspects of the
Java programming language Java is a high-level, class-based, object-oriented programming language that is designed to have as few implementation dependencies as possible. It is a general-purpose programming language intended to let programmers ''write once, run anywh ...
, and
Microsoft Microsoft Corporation is an American multinational technology corporation producing computer software, consumer electronics, personal computers, and related services headquartered at the Microsoft Redmond campus located in Redmond, Washin ...
's C# programming language, which has open implementations of most parts of the system, also has Common Language Runtime (CLR) as a closed environment. Many proprietary languages are widely used, in spite of their proprietary nature; examples include
MATLAB MATLAB (an abbreviation of "MATrix LABoratory") is a proprietary multi-paradigm programming language and numeric computing environment developed by MathWorks. MATLAB allows matrix manipulations, plotting of functions and data, implementa ...
,
VBScript VBScript (''"Microsoft Visual Basic Scripting Edition"'') is an Active Scripting language developed by Microsoft that is modeled on Visual Basic. It allows Microsoft Windows system administrators to generate powerful tools for managing computers ...
, and
Wolfram Language The Wolfram Language ( ) is a general multi-paradigm programming language developed by Wolfram Research. It emphasizes symbolic computation, functional programming, and rule-based programming and can employ arbitrary structures and data. It ...
. Some languages may make the transition from closed to open; for example, Erlang was originally Ericsson's internal programming language.


Use

Thousands of different programming languages have been created, mainly in the computing field. Individual software projects commonly use five programming languages or more. Programming languages differ from most other forms of human expression in that they require a greater degree of precision and completeness. When using a natural language to communicate with other people, human authors and speakers can be ambiguous and make small errors, and still expect their intent to be understood. However, figuratively speaking, computers "do exactly what they are told to do", and cannot "understand" what code the programmer intended to write. The combination of the language definition, a program, and the program's inputs must fully specify the external behavior that occurs when the program is executed, within the domain of control of that program. On the other hand, ideas about an algorithm can be communicated to humans without the precision required for execution by using pseudocode, which interleaves natural language with code written in a programming language. A programming language provides a structured mechanism for defining pieces of data, and the operations or transformations that may be carried out automatically on that data. A programmer uses the abstractions present in the language to represent the concepts involved in a computation. These concepts are represented as a collection of the simplest elements available (called primitives). '' Programming'' is the process by which programmers combine these primitives to compose new programs, or adapt existing ones to new uses or a changing environment. Programs for a computer might be
executed Capital punishment, also known as the death penalty, is the state-sanctioned practice of deliberately killing a person as a punishment for an actual or supposed crime, usually following an authorized, rule-governed process to conclude that t ...
in a batch process without human interaction, or a user might type commands in an interactive session of an interpreter. In this case the "commands" are simply programs, whose execution is chained together. When a language can run its commands through an interpreter (such as a
Unix shell A Unix shell is a command-line interpreter or shell that provides a command line user interface for Unix-like operating systems. The shell is both an interactive command language and a scripting language, and is used by the operating syste ...
or other command-line interface), without compiling, it is called a
scripting language A scripting language or script language is a programming language that is used to manipulate, customize, and automate the facilities of an existing system. Scripting languages are usually interpreted at runtime rather than compiled. A scripting ...
.


Measuring language usage

Determining which is the most widely used programming language is difficult since the definition of usage varies by context. One language may occupy the greater number of programmer hours, a different one has more lines of code, and a third may consume the most CPU time. Some languages are very popular for particular kinds of applications. For example, COBOL is still strong in the corporate data center, often on large
mainframes A mainframe computer, informally called a mainframe or big iron, is a computer used primarily by large organizations for critical applications like bulk data processing for tasks such as censuses, industry and consumer statistics, enterprise ...
; Fortran in scientific and engineering applications;
Ada Ada may refer to: Places Africa * Ada Foah, a town in Ghana * Ada (Ghana parliament constituency) * Ada, Osun, a town in Nigeria Asia * Ada, Urmia, a village in West Azerbaijan Province, Iran * Ada, Karaman, a village in Karaman Province, ...
in aerospace, transportation, military, real-time, and embedded applications; and C in embedded applications and operating systems. Other languages are regularly used to write many different kinds of applications. Various methods of measuring language popularity, each subject to a different bias over what is measured, have been proposed: * counting the number of job advertisements that mention the language * the number of books sold that teach or describe the language * estimates of the number of existing lines of code written in the language which may underestimate languages not often found in public searches * counts of language references (i.e., to the name of the language) found using a web search engine. Combining and averaging information from various internet sites, stackify.com reported the ten most popular programming languages (in descending order by overall popularity):
Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's mos ...
, C,
C++ C++ (pronounced "C plus plus") is a high-level general-purpose programming language created by Danish computer scientist Bjarne Stroustrup as an extension of the C programming language, or "C with Classes". The language has expanded significan ...
,
Python Python may refer to: Snakes * Pythonidae, a family of nonvenomous snakes found in Africa, Asia, and Australia ** ''Python'' (genus), a genus of Pythonidae found in Africa and Asia * Python (mythology), a mythical serpent Computing * Python (pro ...
, C#,
JavaScript JavaScript (), often abbreviated as JS, is a programming language that is one of the core technologies of the World Wide Web, alongside HTML and CSS. As of 2022, 98% of websites use JavaScript on the client side for webpage behavior, of ...
, VB .NET, R,
PHP PHP is a general-purpose scripting language geared toward web development. It was originally created by Danish-Canadian programmer Rasmus Lerdorf in 1993 and released in 1995. The PHP reference implementation is now produced by The PHP Group. ...
, and
MATLAB MATLAB (an abbreviation of "MATrix LABoratory") is a proprietary multi-paradigm programming language and numeric computing environment developed by MathWorks. MATLAB allows matrix manipulations, plotting of functions and data, implementa ...
.


Dialects, flavors and implementations

A dialect of a programming language or a
data exchange language Data exchange is the process of taking data structured under a ''source'' Database schema, schema and transforming it into a ''target'' schema, so that the target data is an accurate representation of the source data.A. Doan, A. Halevy, and Z. Ives ...
is a (relatively small) variation or extension of the language that does not change its intrinsic nature. With languages such as
Scheme A scheme is a systematic plan for the implementation of a certain idea. Scheme or schemer may refer to: Arts and entertainment * ''The Scheme'' (TV series), a BBC Scotland documentary series * The Scheme (band), an English pop band * ''The Schem ...
and
Forth Forth or FORTH may refer to: Arts and entertainment * ''forth'' magazine, an Internet magazine * ''Forth'' (album), by The Verve, 2008 * ''Forth'', a 2011 album by Proto-Kaw * Radio Forth, a group of independent local radio stations in Scotla ...
, standards may be considered insufficient, inadequate, or illegitimate by implementors, so often they will deviate from the standard, making a new
dialect The term dialect (from Latin , , from the Ancient Greek word , 'discourse', from , 'through' and , 'I speak') can refer to either of two distinctly different types of linguistic phenomena: One usage refers to a variety of a language that is a ...
. In other cases, a dialect is created for use in a domain-specific language, often a subset. In the Lisp world, most languages that use basic
S-expression In computer programming, an S-expression (or symbolic expression, abbreviated as sexpr or sexp) is an expression in a like-named notation for nested list (tree-structured) data. S-expressions were invented for and popularized by the programming la ...
syntax and Lisp-like semantics are considered Lisp dialects, although they vary wildly, as do, say, Racket and
Clojure Clojure (, like ''closure'') is a dynamic and functional dialect of the Lisp programming language on the Java platform. Like other Lisp dialects, Clojure treats code as data and has a Lisp macro system. The current development process is comm ...
. As it is common for one language to have several dialects, it can become quite difficult for an inexperienced programmer to find the right documentation. The BASIC programming language has many dialects.


Taxonomies

There is no overarching classification scheme for programming languages. A given programming language does not usually have a single ancestor language. Languages commonly arise by combining the elements of several predecessor languages with new ideas in circulation at the time. Ideas that originate in one language will diffuse throughout a family of related languages, and then leap suddenly across familial gaps to appear in an entirely different family. The task is further complicated by the fact that languages can be classified along multiple axes. For example, Java is both an object-oriented language (because it encourages object-oriented organization) and a concurrent language (because it contains built-in constructs for running multiple threads in parallel).
Python Python may refer to: Snakes * Pythonidae, a family of nonvenomous snakes found in Africa, Asia, and Australia ** ''Python'' (genus), a genus of Pythonidae found in Africa and Asia * Python (mythology), a mythical serpent Computing * Python (pro ...
is an object-oriented
scripting language A scripting language or script language is a programming language that is used to manipulate, customize, and automate the facilities of an existing system. Scripting languages are usually interpreted at runtime rather than compiled. A scripting ...
. In broad strokes, programming languages are classified by ''
programming paradigm Programming paradigms are a way to classify programming languages based on their features. Languages can be classified into multiple paradigms. Some paradigms are concerned mainly with implications for the execution model of the language, suc ...
'' and ''intended domain of use,'' with
general-purpose programming language In computer software, a general-purpose programming language (GPL) is a programming language for building software in a wide variety of application domains. Conversely, a domain-specific programming language is used within a specific area. For exam ...
s distinguished from
domain-specific programming language A domain-specific language (DSL) is a computer language specialized to a particular application domain. This is in contrast to a general-purpose language (GPL), which is broadly applicable across domains. There are a wide variety of DSLs, ranging ...
s. Traditionally, programming languages have been regarded as describing computation in terms of imperative sentences, i.e. issuing commands. These are generally called
imperative programming In computer science, imperative programming is a programming paradigm of software that uses statements that change a program's state. In much the same way that the imperative mood in natural languages expresses commands, an imperative program ...
languages. A great deal of research in programming languages has been aimed at blurring the distinction between a program as a set of instructions and a program as an assertion about the desired answer, which is the main feature of declarative programming. More refined paradigms include
procedural programming Procedural programming is a programming paradigm, derived from imperative programming, based on the concept of the '' procedure call''. Procedures (a type of routine or subroutine) simply contain a series of computational steps to be carrie ...
,
object-oriented programming Object-oriented programming (OOP) is a programming paradigm based on the concept of "objects", which can contain data and code. The data is in the form of fields (often known as attributes or ''properties''), and the code is in the form of ...
,
functional programming In computer science, functional programming is a programming paradigm where programs are constructed by applying and composing functions. It is a declarative programming paradigm in which function definitions are trees of expressions that ...
, and
logic programming Logic programming is a programming paradigm which is largely based on formal logic. Any program written in a logic programming language is a set of sentences in logical form, expressing facts and rules about some problem domain. Major logic pro ...
; some languages are hybrids of paradigms or multi-paradigmatic. An assembly language is not so much a paradigm as a direct model of an underlying machine architecture. By purpose, programming languages might be considered general purpose,
system programming language A system programming language is a programming language used for system programming; such languages are designed for writing system software, which usually requires different development approaches when compared with application software. Edsger W ...
s, scripting languages, domain-specific languages, or concurrent/distributed languages (or a combination of these). Some general purpose languages were designed largely with educational goals. A programming language may also be classified by factors unrelated to the programming paradigm. For instance, most programming languages use
English language English is a West Germanic language of the Indo-European language family, with its earliest forms spoken by the inhabitants of early medieval England. It is named after the Angles, one of the ancient Germanic peoples that migrated to the ...
keywords, while a minority do not. Other languages may be classified as being deliberately esoteric or not.


See also

*
Comparison of programming languages (basic instructions) This article compares a large number of programming languages by tabulating their data types, their expression, statement, and declaration syntax, and some common operating-system interfaces. __TOC__ Conventions of this article Generally, ' ...
*
Comparison of programming languages Programming languages are used for controlling the behavior of a machine (often a computer). Like natural languages, programming languages follow the rules for syntax and semantics. There are thousands of programming languages and new ones are c ...
*
Computer programming Computer programming is the process of performing a particular computation (or more generally, accomplishing a specific computing result), usually by designing and building an executable computer program. Programming involves tasks such as anal ...
*
Computer science Computer science is the study of computation, automation, and information. Computer science spans theoretical disciplines (such as algorithms, theory of computation, information theory, and automation) to practical disciplines (includi ...
and
Outline of computer science Computer science (also called computing science) is the study of the theoretical foundations of information and computation and their implementation and application in computer systems. One well known subject classification system for computer sc ...
* Domain-specific language * Domain-specific modelling *
Educational programming language An educational programming language is a programming language that is designed mostly as an instrument for learning, and less as a tool for writing programs to perform work. Types of educational programming languages Assembly languages Origi ...
*
Esoteric programming language An esoteric programming language (sometimes shortened to esolang) is a programming language designed to test the boundaries of computer programming language design, as a proof of concept, as software art, as a hacking interface to another language ...
*
Extensible programming Extensible programming is a term used in computer science to describe a style of computer programming that focuses on mechanisms to extend the programming language, compiler and runtime environment. Extensible programming languages, supporting this ...
* :Extensible syntax programming languages *
Invariant based programming Invariant-based programmingBack, Ralph-JohanInvariant Based Programming: Basic approach and Teaching Experience Formal Aspects of Computing, 14 February 2008, ISSN 0934-5043 (Print) 1433-299X (Online) is a programming methodology where Formal specif ...
*
List of BASIC dialects This is an alphabetical list of BASIC dialects — interpreted and compiled variants of the BASIC programming language. Each dialect's platform(s), i.e., the computer models and operating systems, are given in parentheses along with any o ...
*
Lists of programming languages There are thousands of programming language A programming language is a system of notation for writing computer programs. Most programming languages are text-based formal languages, but they may also be graphical. They are a kind of comput ...
* List of programming language researchers *
Programming languages used in most popular websites One thing the most visited websites have in common is that they are dynamic websites. Their development typically involves server-side coding, client-side coding and database technology. The programming languages applied to deliver dynamic web ...
*
Language-oriented programming Language-oriented programming (LOP) is a software-development paradigm where "language" is a software building block with the same status as objects, modules and components, and rather than solving problems in general-purpose programming languages, ...
*
Logic programming Logic programming is a programming paradigm which is largely based on formal logic. Any program written in a logic programming language is a set of sentences in logical form, expressing facts and rules about some problem domain. Major logic pro ...
*
Literate programming Literate programming is a programming paradigm introduced in 1984 by Donald Knuth in which a computer program is given as an explanation of its logic in a natural language, such as English, interspersed (embedded) with snippets of macros an ...
*
Metaprogramming Metaprogramming is a programming technique in which computer programs have the ability to treat other programs as their data. It means that a program can be designed to read, generate, analyze or transform other programs, and even modify itself ...
** *
Modeling language A modeling language is any artificial language that can be used to express information or knowledge or systems in a structure that is defined by a consistent set of rules. The rules are used for interpretation of the meaning of components in th ...
* Programming language theory * Pseudocode * *
Reflection Reflection or reflexion may refer to: Science and technology * Reflection (physics), a common wave phenomenon ** Specular reflection, reflection from a smooth surface *** Mirror image, a reflection in a mirror or in water ** Signal reflection, in ...
*
Scientific programming language In computer programming, a scientific programming language can refer to two degrees of the same concept. In a wide sense, a scientific programming language is a programming language that is used widely for computational science and computational ...
*
Scripting language A scripting language or script language is a programming language that is used to manipulate, customize, and automate the facilities of an existing system. Scripting languages are usually interpreted at runtime rather than compiled. A scripting ...
*
Software engineering Software engineering is a systematic engineering approach to software development. A software engineer is a person who applies the principles of software engineering to design, develop, maintain, test, and evaluate computer software. The term '' ...
and
List of software engineering topics The following outline is provided as an overview of and topical guide to software engineering: Software engineering – application of a systematic, disciplined, quantifiable approach to the development, operation, and maintenance of software ...


References


Further reading

* *
Raphael Finkel Raphael Finkel (born 1951) is an American computer scientist and a professor at the University of Kentucky. He compiled the first version of the Jargon File. He is the author of ''An Operating Systems Vade Mecum'',Advanced Programming Language Design
', Addison Wesley 1995. * Daniel P. Friedman,
Mitchell Wand Mitchell Wand is a computer science professor at Northeastern University. He received his Ph.D. from Massachusetts Institute of Technology. His research has centred on programming languages and he is a member of the Northeastern Programming Resea ...
,
Christopher T. Haynes Christopher is the English version of a Europe-wide name derived from the Greek name Χριστόφορος (''Christophoros'' or '' Christoforos''). The constituent parts are Χριστός (''Christós''), "Christ" or "Anointed", and φέρει ...
: ''
Essentials of Programming Languages ''Essentials of Programming Languages'' (''EOPL'') is a textbook on programming languages by Daniel P. Friedman, Mitchell Wand, and Christopher T. Haynes. EOPL surveys the principles of programming languages from an operational perspective. It ...
'', The MIT Press 2001. * Maurizio Gabbrielli and Simone Martini: "Programming Languages: Principles and Paradigms", Springer, 2010. *
David Gelernter David Hillel Gelernter (born March 5, 1955) is an American computer scientist, artist, and writer. He is a professor of computer science at Yale University. Gelernter is known for contributions to parallel computation in the 1980s, and for book ...
,
Suresh Jagannathan Suresh is an Indian masculine Indian given name, given name originating in the Sanskrit word ' (compound of ' and '). Its meaning is "Ruler of Gods" and it has been used an epithet for the Hindu gods Indra, Brahma, Vishnu and Shiva. People named Su ...
: ''Programming Linguistics'',
The MIT Press The MIT Press is a university press affiliated with the Massachusetts Institute of Technology (MIT) in Cambridge, Massachusetts (United States). It was established in 1962. History The MIT Press traces its origins back to 1926 when MIT publish ...
1990. *
Ellis Horowitz Ellis Horowitz is an American computer scientist and Professor of Computer Science and Electrical Engineering at the University of Southern California (USC). Horowitz is best known for his computer science textbooks on data structures and algor ...
(ed.): ''Programming Languages, a Grand Tour'' (3rd ed.), 1987. * Ellis Horowitz: ''Fundamentals of Programming Languages'', 1989. *
Shriram Krishnamurthi Shriram Krishnamurthi is a computer scientist, currently a professor of computer science at Brown University and a member of the core development group for the Racket programming languages, responsible for creation of software packages including ...
: '' Programming Languages: Application and Interpretation''
online publication
* Bruce J. MacLennan: ''Principles of Programming Languages: Design, Evaluation, and Implementation'',
Oxford University Press Oxford University Press (OUP) is the university press of the University of Oxford. It is the largest university press in the world, and its printing history dates back to the 1480s. Having been officially granted the legal right to print books ...
1999. * John C. Mitchell: ''Concepts in Programming Languages'',
Cambridge University Press Cambridge University Press is the university press of the University of Cambridge. Granted letters patent by King Henry VIII in 1534, it is the oldest university press in the world. It is also the King's Printer. Cambridge University Pre ...
2002. * Benjamin C. Pierce: ''
Types and Programming Languages ''Types and Programming Languages'', , is a book by Benjamin C. Pierce on type system In computer programming, a type system is a logical system comprising a set of rules that assigns a property called a type to every "term" (a word, phrase ...
'', The MIT Press 2002. * Terrence W. Pratt and
Marvin Victor Zelkowitz Marvin Victor Zelkowitz (born 7 August 1945) is an American computer scientist and engineer. Zelkowitz earned a degree in mathematics from Rensselaer Polytechnic Institute in 1967 and a master's degree and doctorate in computer science at Corne ...
: ''Programming Languages: Design and Implementation'' (4th ed.), Prentice Hall 2000. *
Peter H. Salus Peter Henry Salus is a linguist, computer scientist, historian of technology, author in many fields, and an editor of books and journals. He has conducted research in germanistics, language acquisition, and computer languages. Education and c ...
. ''Handbook of Programming Languages'' (4 vols.). Macmillan 1998. *
Ravi Sethi Ravi Sethi (born 1947) is an Indian computer scientist retired from executive roles at Bell Labs and Avaya Labs. He also serves as a member of the National Science Foundation's Computer and Information Science and Engineering (CISE) Advisory Co ...
: ''Programming Languages: Concepts and Constructs'', 2nd ed.,
Addison-Wesley Addison-Wesley is an American publisher of textbooks and computer literature. It is an imprint of Pearson PLC, a global publishing and education company. In addition to publishing books, Addison-Wesley also distributes its technical titles throu ...
1996. * Michael L. Scott: ''Programming Language Pragmatics'',
Morgan Kaufmann Publishers Morgan Kaufmann Publishers is a Burlington, Massachusetts (San Francisco, California until 2008) based publisher specializing in computer science and engineering content. Since 1984, Morgan Kaufmann has published content on information technology ...
2005. *
Robert W. Sebesta The name Robert is an ancient Germanic given name, from Proto-Germanic "fame" and "bright" (''Hrōþiberhtaz''). Compare Old Dutch ''Robrecht'' and Old High German ''Hrodebert'' (a compound of '' Hruod'' ( non, Hróðr) "fame, glory, honou ...
: ''Concepts of Programming Languages'', 9th ed., Addison Wesley 2009. *
Franklyn Turbak ''Franklyn'' is a 2008 British science fantasy film written and directed by Gerald McMorrow as his debut feature. Produced by Jeremy Thomas, it stars Ryan Phillippe, Eva Green and Sam Riley. Shooting took place in London in the fourth quarter ...
and
David Gifford David (; , "beloved one") (traditional spelling), , ''Dāwūd''; grc-koi, Δαυΐδ, Dauíd; la, Davidus, David; gez , ዳዊት, ''Dawit''; xcl, Դաւիթ, ''Dawitʿ''; cu, Давíдъ, ''Davidŭ''; possibly meaning "beloved one". w ...
with
Mark Sheldon Mark may refer to: Currency * Bosnia and Herzegovina convertible mark, the currency of Bosnia and Herzegovina * East German mark, the currency of the German Democratic Republic * Estonian mark, the currency of Estonia between 1918 and 1927 * Fin ...
: ''Design Concepts in Programming Languages'', The MIT Press 2009. *
Peter Van Roy Peter may refer to: People * List of people named Peter, a list of people and fictional characters with the given name * Peter (given name) ** Saint Peter (died 60s), apostle of Jesus, leader of the early Christian Church * Peter (surname), a su ...
and Seif Haridi. '' Concepts, Techniques, and Models of Computer Programming'', The MIT Press 2004. *
David A. Watt David Anthony Watt (born 5 November 1946) is a British computer scientist. Watt is a professor at the University of Glasgow, Scotland. With Peter Mosses he developed action semantics, a combination of denotational semantics, operational an ...
. ''Programming Language Concepts and Paradigms''. Prentice Hall 1990. * David A. Watt and
Muffy Thomas Muffy or Muffie is an American nickname and may refer to: People * Muffie Cabot (born c. 1936), American heiress and socialite * Muffy Calder (born 1958), Scottish computer scientist * Marianna Davis (born 1972), American Paralympic cyclist, sit ...
. ''Programming Language Syntax and Semantics''. Prentice Hall 1991. * David A. Watt. ''Programming Language Processors''. Prentice Hall 1993. * David A. Watt. ''Programming Language Design Concepts''. John Wiley & Sons 2004.


External links

{{DEFAULTSORT:Programming Language Programming language classification Notation Articles with example C code