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A programming language is a
formal language In logic, mathematics, computer science, and linguistics, a formal language consists of string (computer science), words whose symbol (formal), letters are taken from an alphabet (computer science), alphabet and are well-formedness, well-formed a ...
comprising a set of
strings String or strings may refer to: *String (structure), a long flexible structure made from threads twisted together, which is used to tie, bind, or hang other objects Arts, entertainment, and media Films * Strings (1991 film), ''Strings'' (1991 fil ...
that produce various kinds of machine code output. Programming languages are one kind of
computer languageComputer language is a formal language In logic, mathematics, computer science, and linguistics, a formal language consists of string (computer science), words whose symbol (formal), letters are taken from an alphabet (computer science), alphabet ...
, and are used in
computer programming Computer programming is the process of designing and building an executable In computing, executable code, an executable file, or an executable program, sometimes simply referred to as an executable or binary, causes a computer "to perform in ...
to implement
algorithm In and , an algorithm () is a finite sequence of , computer-implementable instructions, typically to solve a class of problems or to perform a computation. Algorithms are always and are used as specifications for performing s, , , and other ...

algorithm
s. Most programming languages consist of
instructions Instruction or instructions may refer to: Computing * Instruction, one operation of a processor within a computer architecture instruction set * Computer program, a collection of instructions Music * Instruction (band), a 2002 rock band from New Y ...
for
computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations automatically. Modern computers can perform generic sets of operations known as Computer program, programs. These programs enable compu ...

computer
s. There are programmable machines that use a set of specific instructions, rather than general programming languages. Since the early 1800s, programs have been used to direct the behavior of machines such as
Jacquard loom The Jacquard machine () is a device fitted to a loom A loom is a device used to weave cloth and tapestry. The basic purpose of any loom is to hold the warp threads under tension Tension may refer to: Science * Psychological stress * Tensi ...

Jacquard loom
s,
music box A music box (American English) or musical box (British English) is an automatic musical instrument in a box that produces Musical note, musical notes by using a set of pins placed on a revolving cylinder (geometry), cylinder or disc to pluck ...

music box
es and
player piano A player piano (also known as a pianola) is a self-playing piano The piano is an acoustic Acoustic may refer to: Music Albums * Acoustic (Bayside EP), ''Acoustic'' (Bayside EP) * Acoustic (Britt Nicole EP), ''Acoustic'' (Britt Nicole ...

player piano
s. The programs for these machines (such as a player piano's scrolls) did not produce different behavior in response to different inputs or conditions. Thousands of different programming languages have been created, and more are being created every year. Many programming languages are written in an
imperative Imperative may refer to: *Imperative mood, a grammatical mood (or mode) expressing commands, direct requests, and prohibitions *Imperative programming, a programming paradigm in computer science *Imperative logic *Imperative (film), ''Imperative'' ...
form (i.e., as a sequence of operations to perform) while other languages use the declarative form (i.e. the desired result is specified, not how to achieve it). The description of a programming language is usually split into the two components of
syntax In linguistics, syntax () is the set of rules, principles, and processes that govern the structure of Sentence (linguistics), sentences (sentence structure) in a given Natural language, language, usually including word order. The term ''syntax'' ...
(form) and
semantics Semantics (from grc, σημαντικός ''sēmantikós'', "significant") is the study of 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 o ...
(meaning). Some languages are defined by a specification document (for example, the C programming language is specified by an
ISO The International Organization for Standardization (ISO ) is an international standard An international standard is a technical standard A technical standard is an established norm (social), norm or requirement for a repeatable technical task w ...
Standard) while other languages (such as
Perl Perl is a family of two high-level High-level and low-level, as technical terms, are used to classify, describe and point to specific Objective (goal), goals of a systematic operation; and are applied in a wide range of contexts, such as, for ...
) have a dominant
implementation Implementation is the realization of an application, or execution of a plan A plan is typically any diagram or list of steps with details of timing and resources, used to achieve an Goal, objective to do something. It is commonly understood as ...
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 Programming language theory (PLT) is a branch of computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their applica ...
is a subfield of
computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of , , and . Computer science ...
that deals with the design, implementation, analysis, characterization, and classification of programming languages.


Definitions

A programming language is a notation for writing programs, which are specifications of a computation or
algorithm In and , an algorithm () is a finite sequence of , computer-implementable instructions, typically to solve a class of problems or to perform a computation. Algorithms are always and are used as specifications for performing s, , , and other ...

algorithm
. Some authors restrict the term "programming language" to those languages that can express all possible algorithms. Traits often considered important for what constitutes a programming language include: ; Function and target : A ''computer programming language'' is a
language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be in relation with") is "an apparent answer to the painful divisions between self and other, private and public, and ...
used to write
computer program In imperative programming In computer science, imperative programming is a programming paradigm that uses Statement (computer science), statements that change a program's state (computer science), state. In much the same way that the imperative mo ...
s, which involves a
computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations automatically. Modern computers can perform generic sets of operations known as Computer program, programs. These programs enable compu ...

computer
performing some kind of computation, "The scope of SIGPLAN is the theory, design, implementation, description, and application of computer programming languages – languages that permit the specification of a variety of different computations, thereby providing the user with significant control (immediate or delayed) over the computer's operation." or
algorithm In and , an algorithm () is a finite sequence of , computer-implementable instructions, typically to solve a class of problems or to perform a computation. Algorithms are always and are used as specifications for performing s, , , and other ...

algorithm
and possibly control external devices such as
printers Printers may be: Technology * Printer (publishing) In publishing, printers are both companies A company, abbreviated as co., is a legal entity In law, a legal person is any person A person (plural people or persons) is a being th ...
,
disk drive Disk storage (also sometimes called drive storage) is a general category of storage mechanisms where data is recorded by various electronic, magnetic, optical, or mechanical changes to a surface layer of one or more rotating disks. A disk drive is ...
s,
robot A robot is a machine—especially one programmable by a computer—capable of carrying out a complex series of actions automatically. A robot can be guided by an external control device, or the control may be embedded within. Robots may be ...

robot
s, and so on. For example,
PostScript PostScript (PS) is a page description language In digital printing, a page description language (PDL) is a computer language that describes the appearance of a printed page in a higher level than an actual output bitmap (or generally raster gra ...

PostScript
programs are frequently created by another program to control a computer printer or display. More generally, a programming language may describe computation on some, possibly abstract, machine. It is generally accepted that a complete specification for a programming language includes a description, possibly idealized, of a machine or processor for that language.R. Narasimahan, Programming Languages and Computers: A Unified Metatheory, pp. 189—247 in Franz Alt, Morris Rubinoff (eds.) Advances in computers, Volume 8, Academic Press, 1994, , p.193 : "a complete specification of a programming language must, by definition, include a specification of a processor—idealized, if you will—for that language." he source cites many references to support this statement/ref> 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 language In neuropsychology Neuropsychology is a branch of psychology. It is concerned with how a person's cognition and behavior are related to the brain and the rest of the nervous system. Professionals in this branch of psychology often focus on ...
s in that natural languages are only used for interaction between people, while programming languages also allow humans to communicate instructions to machines. ; Abstractions : Programming languages usually contain
abstractions Abstraction in its main sense is a conceptual process where general rules Rule or ruling may refer to: Human activity * The exercise of political Politics (from , ) is the set of activities that are associated with Decision-making, ma ...
for defining and manipulating
data structure In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of ...

data structure
s 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. ; Expressive power : 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 ...
classifies languages by the computations they are capable of expressing. All
Turing-complete In computability theory Computability theory, also known as recursion theory, is a branch of mathematical logic Mathematical logic, also called formal logic, is a subfield of mathematics Mathematics (from Ancient Greek, Greek: ) include ...
languages can implement the same set of
algorithm In and , an algorithm () is a finite sequence of , computer-implementable instructions, typically to solve a class of problems or to perform a computation. Algorithms are always and are used as specifications for performing s, , , and other ...

algorithm
s. ANSI/ISO SQL-92 and Charity are examples of languages that are not Turing complete, yet are often called programming languages.
Markup languages #REDIRECT Markup language #REDIRECT Markup language In computer text processing, a markup language is a system for annotation, annotating a document in a way that is Syntax (logic), syntactically distinguishable from the text, meaning when the do ...
like
XML Extensible Markup Language (XML) is a markup language #REDIRECT Markup language In computer text processing, a markup language is a system for annotation, annotating a document in a way that is Syntax (logic), syntactically distinguishable fro ...

XML
,
HTML The HyperText Markup Language, or HTML is the standard markup language #REDIRECT Markup language In computer text processing, a markup language is a system for annotation, annotating a document in a way that is Syntax (logic), syntacticall ...

HTML
, or
troff troff (), short for "typesetter roff", is the major component of a document processing system developed by AT&T Corporation for the Unix operating system. troff and the related nroff were both developed from the original roff (computer program) ...
, which define
structured data A data model (or datamodel) 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 ...
, are not usually considered programming languages. Programming languages may, however, share the syntax with markup languages if a computational semantics is defined.
XSLT XSLT (Extensible Stylesheet Language Transformations) is a language for XML transformation language, transforming XML documents into other XML documents, or other formats such as HTML for web pages, plain text or XSL Formatting Objects, which may s ...

XSLT
, for example, is a
Turing complete Alan Mathison Turing (; 23 June 1912 – 7 June 1954) was an English mathematician A mathematician is someone who uses an extensive knowledge of mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such to ...
language entirely using XML syntax. Moreover,
LaTeX Latex is a stable dispersion (emulsion An emulsion is a mixture of two or more liquids that are normally Miscibility, immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class o ...

LaTeX
, which is mostly used for structuring documents, also contains a Turing complete subset. The term ''computer language'' 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. Another usage regards programming languages as theoretical constructs for programming
abstract machine An abstract machine, also called an abstract computer, is a theoretical computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations automatically. Modern computers can perform generic ...
s, and computer languages as the subset thereof that runs on physical computers, which have finite hardware resources. 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 veri ...
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.


History


Early developments

Very early computers, such as
Colossus Colossus, Colossos, or the plural Colossi or Colossuses, comes from the Ancient Greek κολοσσός meaning a giant statue, and may refer to: Statues * Any exceptionally large statue, see List of tallest statues; see also :Colossal statues * ' ...

Colossus
, were programmed without the help of a
stored program A stored-program computer is a computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations automatically. Modern computers can perform generic sets of operations known as Computer pro ...
, by modifying their circuitry or setting banks of physical controls. Slightly later, programs could be written in
machine language In computer programming Computer programming is the process of designing and building an executable computer program to accomplish a specific computing result or to perform a particular task. Programming involves tasks such as analysis, ...
, 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 cardSteven Pinker, in ''The Stuff of Thought'', Viking, 2007, p.362, notes the loss of ''-ed'' in pronunciation ''as it did in ice cream, mincemeat, and box set, formerly iced cream, minced meat, and boxed set.'' or pu ...

punched card
s, paper tape,
magnetic tape Magnetic tape is a medium for , made of a thin, magnetizable coating on a long, narrow strip of . It was developed in Germany in 1928, based on . Devices that record and playback audio and video using magnetic tape are s and s respectively. A ...
or toggled in on switches on the
front panel Front may refer to: Arts, entertainment, and media Films * ''The Front'' (1943 film), a 1943 Soviet drama film * ''The Front ''The Front'' is a 1976 comedy-drama Comedy-drama, or dramedy, is a genre of dramatic works that combines elements ...

front panel
of the computer. Machine languages were later termed ''
first-generation programming language A first-generation programming language (1GL) is a machine-level programming language A programming language is a formal language comprising a Instruction set architecture, set of instructions that produce various kinds of Input/output, output. ...
s'' (1GL). The next step was the development of the so-called ''
second-generation programming languageSecond-generation programming language (2GL) is a generational way to categorize assembly language In computer programming Computer programming is the process of designing and building an executable computer program to accomplish a specific co ...
s'' (2GL) or
assembly language In computer programming Computer programming is the process of designing and building an executable computer program to accomplish a specific computing result or to perform a particular task. Programming involves tasks such as analysis, gene ...
s, which were still closely tied to the
instruction set architecture In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of , ...
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 Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of , , ...
s'', or ''
third-generation programming languageThird generation may refer to: * ''Third Generation'' (album), a 1982 album by Hiroshima * ''The Third Generation'' (1920 film), an American drama film directed by Henry Kolker Joseph Henry Kolker (November 13, 1874 ome sources 1870– July 1 ...
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 A programming language is a formal language comprising a Instruction set architecture, set of instructions that produce various kinds of Input/output, output. Programming languages are used in computer p ...
, developed for the German Z3 by
Konrad Zuse Konrad 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-controlled ...

Konrad Zuse
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 A physicist is a scientist A scientist is a person who conducts Scientific method, scientific research to advance knowledge in an Branches of science, ...
's
Short Code Short Code was one of the first higher-level languages ever developed for an electronic computer Electronic may refer to: *Electronics, the science of how to control electric energy in semiconductor *Electronics (magazine), ''Electronics'' (magazin ...
, proposed in 1949, was one of the first high-level languages ever developed for an
electronic computer Electronic may refer to: *Electronics, the science of how to control electric energy in semiconductor *Electronics (magazine), ''Electronics'' (magazine), a defunct American trade journal *Electronic storage, the storage of data using an electronic ...
.Sebesta, W.S Concepts of Programming languages. 2006;M6 14:18 pp.44. Unlike
machine code In computer programming Computer programming is the process of designing and building an executable computer program to accomplish a specific computing result or to perform a particular task. Programming involves tasks such as analysis, ge ...
, Short Code statements represented mathematical expressions in 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 Univer ...

University of Manchester
,
Alick Glennie Alick Edwards Glennie (1925–2003) was a British people, 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 o ...
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 computer A computer is a machine A machine is a man-made device that uses powe ...
in the early 1950s. As a
programming language A programming language is a formal language In logic, mathematics, computer science, and linguistics, a formal language consists of string (computer science), words whose symbol (formal), letters are taken from an alphabet (computer science) ...
, it used a
compiler In computing, a compiler is a computer program that Translator (computing), translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily ...

compiler
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 Chapter or Chapters may refer to: Books * Chapter (books), a main division of a piece of writing or document * Chapter book, a story book intended for intermediate readers, generally age 7–10 * Chapters (bookstore ...
computer at the University of Manchester and is considered to be the first
compiled In computing, a compiler is a computer program that Translator (computing), translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily ...

compiled
high-level programming language. The second autocode was developed for the Mark 1 by R. A. Brooker in 1954 and was called the "Mark 1 Autocode". Brooker also developed an autocode for the
Ferranti MercuryThe 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 wit ...
in the 1950s in conjunction with the University of Manchester. The version for the
EDSAC 2 EDSAC 2 was an early computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations automatically. Modern computers can perform generic sets of operations known as Computer program, progra ...
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 Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as wel ...
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 optimisation 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), Atlas computer. Th ...
was developed for the University of Manchester Atlas 1 machine. In 1954,
FORTRAN Fortran (; formerly FORTRAN) is a general-purpose, compiled language, compiled imperative programming, imperative programming language that is especially suited to numerical analysis, numeric computation and computational science, scientific com ...

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, FORTRAN, the first widely used high-level programming language, and was the inventor of ...

John Backus
. 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 A supercomputer is a computer with a high level of performance as compared to a general-purpose computer. The performance of a supercomputer is commonly measured in floating-point operations per second (FLOPS) instead of million instructions p ...
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 Murray Hopper ( December 9, 1906 – January 1, 1992) was an American computer scientist and United States Navy ), (unofficial)."''Non sibi sed patriae''" ( en, "Not for self but for country") (unofficial). , colors ...

Grace Hopper
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 The UNIVAC I (UNIVersal Automatic Computer I) was the first general-purpose electronic digit ...
. 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 . It was designed principally by and , the inventors of the . Design work was started by th ...
at
Remington Rand Remington Rand was an early American business machine manufacturer, best known originally as a typewriter Video showing the operation of a typewriter A typewriter is a mechanical Mechanical may refer to: Machine * Mechanical system A ...
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 is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon England, early medieval England, which has eventually become the World language, leading lan ...

English
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 COBOL (; an acronym An acronym is a word In linguistics, a word of a spoken language can be defined as the smallest sequence of phonemes that can be uttered in isolation with semantic, objective or pragmatics, practical meaning (linguis ...

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, d ...
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 A programming language is a formal language comprising a Instruction set architecture, set of instructions that produce various kinds of Input/output, output. Programming languages ar ...
s'' or ''
system programming language A system programming language is a programming language A programming language is a formal language comprising a Instruction set architecture, set of instructions that produce various kinds of Input/output, output. Programming languages are use ...
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 progra ...
'' and influenced
functional programming In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of , ...
. *
ALGOL ALGOL (; short for "Algorithmic Language") is a family of imperative Imperative may refer to: *Imperative mood, a grammatical mood (or mode) expressing commands, direct requests, and prohibitions *Imperative programming, a programming paradigm ...
refined both ''structured procedural programming'' and the discipline of
language specificationIn computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development of both computer hardware , hardware and software. ...
; the "Revised Report on the Algorithmic Language
ALGOL 60 ALGOL 60 (short for ''Algorithmic Language 1960'') is a member of the ALGOL Algol , designated Beta Persei (β Persei, abbreviated Beta Per, β Per), known colloquially as the Demon Star, is a bright multiple st ...
" became a model for how later language specifications were written. *
Lisp Lisp (historically LISP) is a family of programming language A programming language is a formal language In logic, mathematics, computer science, and linguistics, a formal language consists of string (computer science), words whose symbo ...
, implemented in 1958, was the first dynamically typed ''
functional programming In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of , ...
'' language. * In the 1960s,
Simula Simula is the name of two simulation A simulation is the imitation of the operation of a real-world process or system over time. Simulations require the use of Conceptual model, models; the model represents the key characteristics or behavio ...
was the first language designed to support ''
object-oriented programming Object-oriented programming (OOP) is a 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 mai ...
''; in the mid-1970s,
Smalltalk Smalltalk is an object-oriented programming, object-oriented, dynamically typed reflection (computer science), reflective programming language. Smalltalk was created as the language underpinning the "new world" of computing exemplified by "human ...

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 Multi-user software is computer software Software is a collection of Instruction (computer science), instructions that tell a computer how to work. This is in contrast t ...

Unix
operating system and remains popular. *
Prolog Prolog is a 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 ...

Prolog
, 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 prog ...
'' language. * In 1978, ML built a polymorphic type system on top of
Lisp Lisp (historically LISP) is a family of programming language A programming language is a formal language In logic, mathematics, computer science, and linguistics, a formal language consists of string (computer science), words whose symbo ...
, pioneering ''
statically typed In programming language A programming language is a formal language comprising a Instruction set architecture, set of instructions that produce various kinds of Input/output, output. Programming languages are used in computer programming to i ...
functional programming In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of , ...
'' 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 Structured programming is a 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 impli ...
'', 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 A computer programmer, sometimes called a software developer, a programmer or more recently a coder (especially in more informal contexts), i ...
, in a famous 1968 letter published in the
Communications of the ACM ''Communications of the ACM'' is the monthly journal A journal, from the Old French ''journal'' (meaning "daily"), may refer to: *Bullet journal, a method of personal organizations *Diary, a record of what happened over the course of a day or othe ...
, argued that
Goto GoTo (goto, GOTO, GO TO or other case combinations, depending on the programming language) is a statement Statement or statements may refer to: Common uses *Statement (computer science), the smallest standalone element of an imperative programmin ...
statements should be eliminated from all "higher level" programming languages.


Consolidation and growth

The 1980s were years of relative consolidation.
C++ C++ () is a general-purpose programming language In computer software, a general-purpose programming language is a programming language dedicated to a general-purpose, designed to be used for writing software in a wide variety of application ...

C++
combined object-oriented and systems programming. The United States government standardized
Ada Ada may refer to: Places Africa * Ada Foah Ada Foah is a town on the southeast coast of Ghana, where the Volta River meets the Atlantic Ocean. The town is located along the Volta River, off of the Accra-Aflao motorway. Known for Palm tree, pal ...
, a systems programming language derived from
Pascal Pascal, Pascal's or PASCAL may refer to: People and fictional characters * Pascal (given name), including a list of people with the name * Pascal (surname), including a list of people and fictional characters with the name ** Blaise Pascal, French ...
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 Modula-2 is a structured, procedural programming language A programming language is a formal language comprising a Instruction set architecture, set of instructions that produce various kinds of Input/output, output. Programming languages are ...
, 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 Computer programming is the process of designing and building an executable computer program to accomplish a specific computing result or to perform a specific task. Programming involves ...
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 ''internetworking, network of networks'' that consist ...

Internet
in the mid-1990s created opportunities for new languages.
Perl Perl is a family of two high-level High-level and low-level, as technical terms, are used to classify, describe and point to specific Objective (goal), goals of a systematic operation; and are applied in a wide range of contexts, such as, for ...
, originally a Unix scripting tool first released in 1987, became common in dynamic
website A website (also written as web site) is a collection of web page A web page (or webpage) is a hypertext Hypertext is text displayed on a or other with references () to other text that the reader can immediately access. Hyperte ...

website
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 147.7 million people, Java is the world's List of ...
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 anywhereWrite once, run anywhere (WORA), or sometimes Write once, run everywhere (WORE), was a 1995 slogan created by Sun Microsystems Sun Microsystems, Inc. (Sun for short) is a defunct American company that sold computers, computer components, software ...
" (
UCSD Pascal UCSD Pascal is a Pascal programming language Pascal is an imperative and procedural programming language A programming language is a formal language comprising a Instruction set architecture, set of instructions that produce various kinds ...
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 (mixins, Delegation (programming), delegates, aspect-oriented programming, aspects), and database integration such as Microsoft's Language Integrated Query, LINQ. ''Fourth-generation programming languages'' (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 and , an algorithm () is a finite sequence of , computer-implementable instructions, typically to solve a class of problems or to perform a computation. Algorithms are always and are used as specifications for performing s, , , and other ...

algorithm
written by a programmer.


Elements

All programming languages have some language primitive, 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 (programming languages), 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, there are some programming languages which are more visual programming language, graphical 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 semantics of programming languages, formal or hard-coded in a Reference implementation (computing), reference implementation). Since most languages are textual, this article discusses textual syntax. Programming language syntax is usually defined using a combination of regular expressions (for lexical analysis, lexical structure) and Backus–Naur form (for context-free grammar, grammatical structure). Below is a simple grammar, based on
Lisp Lisp (historically LISP) is a family of programming language A programming language is a formal language In logic, mathematics, computer science, and linguistics, a formal language consists of string (computer science), words whose symbo ...
: 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. 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 In neuropsychology Neuropsychology is a branch of psychology. It is concerned with how a person's cognition and behavior are related to the brain and the rest of the nervous system. Professionals in this branch of psychology often focus on ...
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-formedness, well-formed but expresses a meaning that cannot be true. The following C (programming language), C language 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 on the first line were omitted, the program would trigger an error on 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. 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, and generally blur the distinction between parsing and execution. In contrast to Lisp macro, 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#Computer science, ''semantics'' refers to the meaning of languages, as opposed to their form (#Syntax, syntax).


Static semantics

The 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 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 called a type system. Other forms of static code analysis, static analyses like data flow analysis 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 147.7 million people, Java is the world's List of ...
and C Sharp (programming language), 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 evaluation strategy, strategy by which expressions are evaluated to values, or the manner in which control flow, control structures conditionally execute Statement (computer science), statements. 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, which allow 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 Decidability (logic), 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 Type conversion#Explicit type conversion, 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 checking, type check programs, but a number of languages, usually functional ones, type inference, 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''.


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 literal, 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 handling, 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 Standard Generalized Markup Language, 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 language In computer programming Computer programming is the process of designing and building an executable computer program to accomplish a specific computing result or to perform a particular task. Programming involves tasks such as analysis, gene ...
s, allows any operation to be performed on any data, generally sequences of bits of various lengths. High-level untyped languages include BCPL, Tcl, and some varieties of Forth (programming language), Forth. In practice, while few languages are considered typed from the type theory (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 Type conversion#Explicit type conversion, casting).


Static versus dynamic typing

In ''Type system, static typing'', 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 ''Manifest typing, manifestly typed'' or ''Type inference, type-inferred''. In the first case, the programmer must explicitly write types at certain textual positions (for example, at variable declaration (computer science), 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++ () is a general-purpose programming language In computer software, a general-purpose programming language is a programming language dedicated to a general-purpose, designed to be used for writing software in a wide variety of application ...

C++
, C Sharp (programming language), 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 147.7 million people, Java is the world's List of ...
, are manifestly typed. Complete type inference has traditionally been associated with less mainstream languages, such as Haskell (programming language), Haskell and ML. However, many manifestly typed languages support partial type inference; for example,
C++ C++ () is a general-purpose programming language In computer software, a general-purpose programming language is a programming language dedicated to a general-purpose, designed to be used for writing software in a wide variety of application ...

C++
,
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 147.7 million people, Java is the world's List of ...
and C Sharp (programming language), 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. ''Type system, Dynamic typing'', 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 Software bug, errors cannot be automatically detected until a piece of code is actually executed, potentially making debugging more difficult.
Lisp Lisp (historically LISP) is a family of programming language A programming language is a formal language In logic, mathematics, computer science, and linguistics, a formal language consists of string (computer science), words whose symbo ...
,
Smalltalk Smalltalk is an object-oriented programming, object-oriented, dynamically typed reflection (computer science), reflective programming language. Smalltalk was created as the language underpinning the "new world" of computing exemplified by "human ...

Smalltalk
,
Perl Perl is a family of two high-level High-level and low-level, as technical terms, are used to classify, describe and point to specific Objective (goal), goals of a systematic operation; and are applied in a wide range of contexts, such as, for ...
, Python (programming language), Python, JavaScript, and Ruby (programming language), Ruby are all examples of dynamically typed languages.


Weak and strong typing

''Weak typing'' allows a value of one type to be treated as another, for example treating a String (computer science), 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 and even at Run time (program lifecycle phase), run time. ''Strongly typed programming language, 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 ''type safety, safe''. An alternative definition for "weakly typed" refers to languages, such as
Perl Perl is a family of two high-level High-level and low-level, as technical terms, are used to classify, describe and point to specific Objective (goal), goals of a systematic operation; and are applied in a wide range of contexts, such as, for ...
and JavaScript, 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 for casting of 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 (computing), library (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 147.7 million people, Java is the world's List of ...
, a string literal is defined as an instance of the java.lang.String class; similarly, in
Smalltalk Smalltalk is an object-oriented programming, object-oriented, dynamically typed reflection (computer science), reflective programming language. Smalltalk was created as the language underpinning the "new world" of computing exemplified by "human ...

Smalltalk
, an anonymous function expression (a "block") constructs an instance of the library's BlockContext class. Conversely, Scheme (programming language), Scheme 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 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 (computer science), 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 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 as "foolish". Alan Perlis 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 programmer, users and the programming language implementation, implementors can use to agree upon whether a piece of source code is a valid computer program, program 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 In neuropsychology Neuropsychology is a branch of psychology. It is concerned with how a person's cognition and behavior are related to the brain and the rest of the nervous system. Professionals in this branch of psychology often focus on ...
(e.g., as in the C (programming language), C language), or a formal semantics of programming languages, formal semantics (e.g., as in Standard ML and Scheme (programming language), Scheme specifications). * A description of the behavior of a compiler, translator for the language (e.g., the
C++ C++ () is a general-purpose programming language In computer software, a general-purpose programming language is a programming language dedicated to a general-purpose, designed to be used for writing software in a wide variety of application ...

C++
and Fortran specifications). The syntax and semantics of the language have to be inferred from this description, which may be written in natural or a formal language. * A reference implementation, ''reference'' or ''model'' implementation, sometimes Meta-circular evaluator, written in the language being specified (e.g.,
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Prolog
or REXX, 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: ''compiler, compilation'' and ''interpreter (computing), 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 Translator (computing), translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily ...

compiler
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 a 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. Here the virtual machine, just before execution, translates the blocks of bytecode 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 languages or internal scripting languages 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, and Microsoft's C Sharp (programming language), 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, VBScript, and Wolfram Language. Some languages may make the transition from closed to open; for example, Erlang (programming language), Erlang was originally an 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 Abstraction (computer science), 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 language primitive, primitives). ''Computer Programming, 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 Execution (computing), executed in a Batch processing, batch process without human interaction, or a user might type Command (computing), commands in an Session (computer science), interactive session of an Interpreter (computing), 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 or other command-line interface), without compiling, it is called a scripting language.


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 COBOL (; an acronym An acronym is a word In linguistics, a word of a spoken language can be defined as the smallest sequence of phonemes that can be uttered in isolation with semantic, objective or pragmatics, practical meaning (linguis ...

COBOL
is still strong in the corporate data center, often on large Mainframe computer, mainframes; Fortran in scientific and engineering applications;
Ada Ada may refer to: Places Africa * Ada Foah Ada Foah is a town on the southeast coast of Ghana, where the Volta River meets the Atlantic Ocean. The town is located along the Volta River, off of the Accra-Aflao motorway. Known for Palm tree, pal ...
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 as (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 147.7 million people, Java is the world's List of ...
, C,
C++ C++ () is a general-purpose programming language In computer software, a general-purpose programming language is a programming language dedicated to a general-purpose, designed to be used for writing software in a wide variety of application ...

C++
, Python (programming language), Python, C Sharp (programming language), C#, JavaScript, Visual Basic .NET, VB .NET, R (programming language), R, PHP, and MATLAB.


Dialects, flavors and implementations

A dialect of a programming language or a data exchange language is a (relatively small) variation or extension of the language that does not change its intrinsic nature. With languages such as Scheme (programming language), Scheme and Forth (programming language), Forth, standards may be considered insufficient, inadequate or illegitimate by implementors, so often they will deviate from the standard, making a new dialect. In other cases, a dialect is created for use in a domain-specific language, often a subset. In the Common Lisp, Lisp world, most languages that use basic S-expression syntax and Lisp-like semantics are considered Lisp dialects, although they vary wildly, as do, say, Racket (programming language), Racket and Clojure. 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 List of BASIC dialects, many dialects. The explosion of Forth dialects led to the saying "If you've seen one Forth... you've seen ''one'' Forth."


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 Thread (computer science), threads in parallel). Python (programming language), Python is an object-oriented scripting language. In broad strokes, programming languages divide into ''programming paradigms'' and a classification by ''intended domain of use,'' with general-purpose programming languages distinguished from domain-specific programming languages. Traditionally, programming languages have been regarded as describing computation in terms of imperative sentences, i.e. issuing commands. These are generally called imperative programming 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,
object-oriented programming Object-oriented programming (OOP) is a 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 mai ...
,
functional programming In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of , ...
, 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 prog ...
; some languages are hybrids of paradigms or multi-paradigmatic. An
assembly language In computer programming Computer programming is the process of designing and building an executable computer program to accomplish a specific computing result or to perform a particular task. Programming involves tasks such as analysis, gene ...
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 A programming language is a formal language comprising a Instruction set architecture, set of instructions that produce various kinds of Input/output, output. Programming languages are use ...
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 programming paradigm. For instance, most programming languages use English language keywords, while Non-English-based programming languages, a minority do not. Other languages may be classified as being Esoteric programming language, deliberately esoteric or not.


See also

* Comparison of programming languages (basic instructions) * Comparison of programming languages * Computer programming * Computer science and Outline of computer science * Domain-specific language * Domain-specific modelling * Educational programming language * Esoteric programming language * Extensible programming * :Extensible syntax programming languages * Invariant based programming * List of BASIC dialects * Lists of programming languages * List of programming language researchers * Programming languages used in most popular websites * Language-oriented programming * Logic programming * Literate programming * Metaprogramming ** * Modeling language *
Programming language theory Programming language theory (PLT) is a branch of computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their applica ...
* Pseudocode * * Reflection (computer science), Reflection * Scientific programming language * Scripting language * Software engineering and List of software engineering topics


References


Further reading

* * Raphael Finkel:
Advanced Programming Language Design
', Addison Wesley 1995. * Daniel P. Friedman, Mitchell Wand, Christopher T. Haynes: ''Essentials of Programming Languages'', The MIT Press 2001. * Maurizio Gabbrielli and Simone Martini: "Programming Languages: Principles and Paradigms", Springer, 2010. * David Gelernter, Suresh Jagannathan: ''Programming Linguistics'', The MIT Press 1990. * Ellis Horowitz (ed.): ''Programming Languages, a Grand Tour'' (3rd ed.), 1987. * Ellis Horowitz: ''Fundamentals of Programming Languages'', 1989. * Shriram Krishnamurthi: ''Programming Languages: Application and Interpretation''
online publication
* Bruce J. MacLennan: ''Principles of Programming Languages: Design, Evaluation, and Implementation'', Oxford University Press 1999. * John C. Mitchell: ''Concepts in Programming Languages'', Cambridge University Press 2002. * Benjamin C. Pierce: ''Types and Programming Languages'', The MIT Press 2002. * Terrence W. Pratt and Marvin V. Zelkowitz: ''Programming Languages: Design and Implementation'' (4th ed.), Prentice Hall 2000. * Peter H. Salus. ''Handbook of Programming Languages'' (4 vols.). Macmillan 1998. * Ravi Sethi: ''Programming Languages: Concepts and Constructs'', 2nd ed., Addison-Wesley 1996. * Michael L. Scott: ''Programming Language Pragmatics'', Morgan Kaufmann Publishers 2005. * Robert W. Sebesta: ''Concepts of Programming Languages'', 9th ed., Addison Wesley 2009. * Franklyn Turbak and David Gifford with Mark Sheldon: ''Design Concepts in Programming Languages'', The MIT Press 2009. * Peter Van Roy and Seif Haridi. ''Concepts, Techniques, and Models of Computer Programming'', The MIT Press 2004. * David A. Watt. ''Programming Language Concepts and Paradigms''. Prentice Hall 1990. * David A. Watt and Muffy Thomas. ''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 Programming languages, Notation Articles with example C code