Programming language

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A programming language is a formal language comprising a set of instructions that produce various kinds of output. Programming language_sentence_0

Programming languages are used in computer programming to implement algorithms. Programming language_sentence_1

Most programming languages consist of instructions for computers. Programming language_sentence_2

There are programmable machines that use a set of specific instructions, rather than general programming languages. Programming language_sentence_3

Since the early 1800s, programs have been used to direct the behavior of machines such as Jacquard looms, music boxes and player pianos. Programming language_sentence_4

The programs for these machines (such as a player piano's scrolls) did not produce different behavior in response to different inputs or conditions. Programming language_sentence_5

Thousands of different programming languages have been created, and more are being created every year. Programming language_sentence_6

Many programming languages are written in an 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). Programming language_sentence_7

The description of a programming language is usually split into the two components of syntax (form) and semantics (meaning). Programming language_sentence_8

Some languages are defined by a specification document (for example, the C programming language is specified by an ISO Standard) while other languages (such as Perl) have a dominant implementation that is treated as a reference. Programming language_sentence_9

Some languages have both, with the basic language defined by a standard and extensions taken from the dominant implementation being common. Programming language_sentence_10

Definitions Programming language_section_0

A programming language is a notation for writing programs, which are specifications of a computation or algorithm. Programming language_sentence_11

Some authors restrict the term "programming language" to those languages that can express all possible algorithms. Programming language_sentence_12

Traits often considered important for what constitutes a programming language include: Programming language_sentence_13

Programming language_description_list_0

  • Function and target: A computer programming language is a language used to write computer programs, which involves a computer performing some kind of computation or algorithm and possibly control external devices such as printers, disk drives, robots, and so on. For example, 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. 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 that natural languages are only used for interaction between people, while programming languages also allow humans to communicate instructions to machines.Programming language_item_0_0
  • 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.Programming language_item_0_1
  • Expressive power: The theory of computation classifies languages by the computations they are capable of expressing. All Turing complete languages can implement the same set of algorithms. ANSI/ISO SQL-92 and Charity are examples of languages that are not Turing complete, yet are often called programming languages.Programming language_item_0_2

Markup languages like XML, HTML, or troff, which define structured data, are not usually considered programming languages. Programming language_sentence_14

Programming languages may, however, share the syntax with markup languages if a computational semantics is defined. Programming language_sentence_15

XSLT, for example, is a Turing complete language entirely using XML syntax. Programming language_sentence_16

Moreover, LaTeX, which is mostly used for structuring documents, also contains a Turing complete subset. Programming language_sentence_17

The term computer language is sometimes used interchangeably with programming language. Programming language_sentence_18

However, the usage of both terms varies among authors, including the exact scope of each. Programming language_sentence_19

One usage describes programming languages as a subset of computer languages. Programming language_sentence_20

Similarly, languages used in computing that have a different goal than expressing computer programs are generically designated computer languages. Programming language_sentence_21

For instance, markup languages are sometimes referred to as computer languages to emphasize that they are not meant to be used for programming. Programming language_sentence_22

Another usage regards programming languages as theoretical constructs for programming abstract machines, and computer languages as the subset thereof that runs on physical computers, which have finite hardware resources. Programming language_sentence_23

John C. Reynolds emphasizes that formal specification languages are just as much programming languages as are the languages intended for execution. Programming language_sentence_24

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. Programming language_sentence_25

History Programming language_section_1

Main article: History of programming languages Programming language_sentence_26

Early developments Programming language_section_2

Very early computers, such as Colossus, were programmed without the help of a stored program, by modifying their circuitry or setting banks of physical controls. Programming language_sentence_27

Slightly later, programs could be written in machine language, where the programmer writes each instruction in a numeric form the hardware can execute directly. Programming language_sentence_28

For example, the instruction to add the value in two memory location might consist of 3 numbers: an "opcode" that selects the "add" operation, and two memory locations. Programming language_sentence_29

The programs, in decimal or binary form, were read in from punched cards, paper tape, magnetic tape or toggled in on switches on the front panel of the computer. Programming language_sentence_30

Machine languages were later termed first-generation programming languages (1GL). Programming language_sentence_31

The next step was the development of the so-called second-generation programming languages (2GL) or assembly languages, which were still closely tied to the instruction set architecture of the specific computer. Programming language_sentence_32

These served to make the program much more human-readable and relieved the programmer of tedious and error-prone address calculations. Programming language_sentence_33

The first high-level programming languages, or third-generation programming languages (3GL), were written in the 1950s. Programming language_sentence_34

An early high-level programming language to be designed for a computer was Plankalkül, developed for the German Z3 by Konrad Zuse between 1943 and 1945. Programming language_sentence_35

However, it was not implemented until 1998 and 2000. Programming language_sentence_36

John Mauchly's Short Code, proposed in 1949, was one of the first high-level languages ever developed for an electronic computer. Programming language_sentence_37

Unlike machine code, Short Code statements represented mathematical expressions in understandable form. Programming language_sentence_38

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. Programming language_sentence_39

At the University of Manchester, Alick Glennie developed Autocode in the early 1950s. Programming language_sentence_40

As a programming language, it used a compiler to automatically convert the language into machine code. Programming language_sentence_41

The first code and compiler was developed in 1952 for the Mark 1 computer at the University of Manchester and is considered to be the first compiled high-level programming language. Programming language_sentence_42

The second autocode was developed for the Mark 1 by R. Programming language_sentence_43 A. Brooker in 1954 and was called the "Mark 1 Autocode". Programming language_sentence_44

Brooker also developed an autocode for the Ferranti Mercury in the 1950s in conjunction with the University of Manchester. Programming language_sentence_45

The version for the EDSAC 2 was devised by D. Programming language_sentence_46 F. Hartley of University of Cambridge Mathematical Laboratory in 1961. Programming language_sentence_47

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. Programming language_sentence_48

A contemporary but separate thread of development, Atlas Autocode was developed for the University of Manchester Atlas 1 machine. Programming language_sentence_49

In 1954, FORTRAN was invented at IBM by John Backus. Programming language_sentence_50

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. Programming language_sentence_51

It is still a popular language for high-performance computing and is used for programs that benchmark and rank the world's fastest supercomputers. Programming language_sentence_52

Another early programming language was devised by Grace Hopper in the US, called FLOW-MATIC. Programming language_sentence_53

It was developed for the UNIVAC I at Remington Rand during the period from 1955 until 1959. Programming language_sentence_54

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 programming language and implemented a prototype. Programming language_sentence_55

The FLOW-MATIC compiler became publicly available in early 1958 and was substantially complete in 1959. Programming language_sentence_56

FLOW-MATIC was a major influence in the design of COBOL, since only it and its direct descendant AIMACO were in actual use at the time. Programming language_sentence_57

Refinement Programming language_section_3

The increased use of high-level languages introduced a requirement for low-level programming languages or system programming languages. Programming language_sentence_58

These languages, to varying degrees, provide facilities between assembly languages and high-level languages. Programming language_sentence_59

They can be used to perform tasks that require direct access to hardware facilities but still provide higher-level control structures and error-checking. Programming language_sentence_60

The period from the 1960s to the late 1970s brought the development of the major language paradigms now in use: Programming language_sentence_61

Programming language_unordered_list_1

Each of these languages spawned descendants, and most modern programming languages count at least one of them in their ancestry. Programming language_sentence_62

The 1960s and 1970s also saw considerable debate over the merits of structured programming, and whether programming languages should be designed to support it. Programming language_sentence_63

Edsger Dijkstra, in a famous 1968 letter published in the Communications of the ACM, argued that Goto statements should be eliminated from all "higher level" programming languages. Programming language_sentence_64

Consolidation and growth Programming language_section_4

The 1980s were years of relative consolidation. Programming language_sentence_65

C++ combined object-oriented and systems programming. Programming language_sentence_66

The United States government standardized Ada, a systems programming language derived from Pascal and intended for use by defense contractors. Programming language_sentence_67

In Japan and elsewhere, vast sums were spent investigating the so-called "fifth-generation" languages that incorporated logic programming constructs. Programming language_sentence_68

The functional languages community moved to standardize ML and Lisp. Programming language_sentence_69

Rather than inventing new paradigms, all of these movements elaborated upon the ideas invented in the previous decades. Programming language_sentence_70

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. Programming language_sentence_71

Modula-2, Ada, and ML all developed notable module systems in the 1980s, which were often wedded to generic programming constructs. Programming language_sentence_72

The rapid growth of the Internet in the mid-1990s created opportunities for new languages. Programming language_sentence_73

Perl, originally a Unix scripting tool first released in 1987, became common in dynamic websites. Programming language_sentence_74

Java 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" (UCSD Pascal had been popular for a time in the early 1980s). Programming language_sentence_75

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_sentence_76

Programming language evolution continues, in both industry and research. Programming language_sentence_77

Current directions include security and reliability verification, new kinds of modularity (mixins, delegates, aspects), and database integration such as Microsoft's LINQ. Programming language_sentence_78

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. Programming language_sentence_79

Fifth-generation programming languages (5GL) are programming languages based on solving problems using constraints given to the program, rather than using an algorithm written by a programmer. Programming language_sentence_80

Elements Programming language_section_5

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). Programming language_sentence_81

These primitives are defined by syntactic and semantic rules which describe their structure and meaning respectively. Programming language_sentence_82

Syntax Programming language_section_6

Main article: Syntax (programming languages) Programming language_sentence_83

A programming language's surface form is known as its syntax. Programming language_sentence_84

Most programming languages are purely textual; they use sequences of text including words, numbers, and punctuation, much like written natural languages. Programming language_sentence_85

On the other hand, there are some programming languages which are more graphical in nature, using visual relationships between symbols to specify a program. Programming language_sentence_86

The syntax of a language describes the possible combinations of symbols that form a syntactically correct program. Programming language_sentence_87

The meaning given to a combination of symbols is handled by semantics (either formal or hard-coded in a reference implementation). Programming language_sentence_88

Since most languages are textual, this article discusses textual syntax. Programming language_sentence_89

Programming language syntax is usually defined using a combination of regular expressions (for lexical structure) and Backus–Naur form (for grammatical structure). Programming language_sentence_90

Below is a simple grammar, based on Lisp: Programming language_sentence_91

This grammar specifies the following: Programming language_sentence_92

Programming language_unordered_list_2

  • an expression is either an atom or a list;Programming language_item_2_10
  • an atom is either a number or a symbol;Programming language_item_2_11
  • a number is an unbroken sequence of one or more decimal digits, optionally preceded by a plus or minus sign;Programming language_item_2_12
  • a symbol is a letter followed by zero or more of any characters (excluding whitespace); andProgramming language_item_2_13
  • a list is a matched pair of parentheses, with zero or more expressions inside it.Programming language_item_2_14

The following are examples of well-formed token sequences in this grammar: 12345, () and (a b c232 (1)). Programming language_sentence_93

Not all syntactically correct programs are semantically correct. Programming language_sentence_94

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. Programming language_sentence_95

In some cases, such programs may exhibit undefined behavior. Programming language_sentence_96

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. Programming language_sentence_97

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: Programming language_sentence_98

Programming language_unordered_list_3

  • "Colorless green ideas sleep furiously." is grammatically well-formed but has no generally accepted meaning.Programming language_item_3_15
  • "John is a married bachelor." is grammatically well-formed but expresses a meaning that cannot be true.Programming language_item_3_16

The following 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): Programming language_sentence_99

If the type declaration on the first line were omitted, the program would trigger an error on undefined variable "p" during compilation. Programming language_sentence_100

However, the program would still be syntactically correct since type declarations provide only semantic information. Programming language_sentence_101

The grammar needed to specify a programming language can be classified by its position in the Chomsky hierarchy. Programming language_sentence_102

The syntax of most programming languages can be specified using a Type-2 grammar, i.e., they are context-free grammars. Programming language_sentence_103

Some languages, including Perl and Lisp, contain constructs that allow execution during the parsing phase. Programming language_sentence_104

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. Programming language_sentence_105

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. Programming language_sentence_106

Semantics Programming language_section_7

The term semantics refers to the meaning of languages, as opposed to their form (syntax). Programming language_sentence_107

Static semantics Programming language_section_8

The static semantics defines restrictions on the structure of valid texts that are hard or impossible to express in standard syntactic formalisms. Programming language_sentence_108

For compiled languages, static semantics essentially include those semantic rules that can be checked at compile time. Programming language_sentence_109

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. Programming language_sentence_110

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. Programming language_sentence_111

Other forms of static analyses like data flow analysis may also be part of static semantics. Programming language_sentence_112

Newer programming languages like Java and C# have definite assignment analysis, a form of data flow analysis, as part of their static semantics. Programming language_sentence_113

Dynamic semantics Programming language_section_9

Main article: Semantics of programming languages Programming language_sentence_114

Once data has been specified, the machine must be instructed to perform operations on the data. Programming language_sentence_115

For example, the semantics may define the strategy by which expressions are evaluated to values, or the manner in which control structures conditionally execute statements. Programming language_sentence_116

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. Programming language_sentence_117

There are many ways of defining execution semantics. Programming language_sentence_118

Natural language is often used to specify the execution semantics of languages commonly used in practice. Programming language_sentence_119

A significant amount of academic research went into formal semantics of programming languages, which allow execution semantics to be specified in a formal manner. Programming language_sentence_120

Results from this field of research have seen limited application to programming language design and implementation outside academia. Programming language_sentence_121

Type system Programming language_section_10

Main articles: Data type, Type system, and Type safety Programming language_sentence_122

A type system defines how a programming language classifies values and expressions into types, how it can manipulate those types and how they interact. Programming language_sentence_123

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. Programming language_sentence_124

Any decidable type system involves a trade-off: while it rejects many incorrect programs, it can also prohibit some correct, albeit unusual programs. Programming language_sentence_125

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. Programming language_sentence_126

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. Programming language_sentence_127

The formal design and study of type systems is known as type theory. Programming language_sentence_128

Typed versus untyped languages Programming language_section_11

A language is typed if the specification of every operation defines types of data to which the operation is applicable. Programming language_sentence_129

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. Programming language_sentence_130

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. Programming language_sentence_131

Many languages allow a function called an exception handler to handle this exception and, for example, always return "-1" as the result. Programming language_sentence_132

A special case of typed languages are the single-typed languages. Programming language_sentence_133

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. Programming language_sentence_134

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. Programming language_sentence_135

High-level untyped languages include BCPL, Tcl, and some varieties of Forth. Programming language_sentence_136

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. Programming language_sentence_137

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). Programming language_sentence_138

Static versus dynamic typing Programming language_section_12

In static typing, all expressions have their types determined prior to when the program is executed, typically at compile-time. Programming language_sentence_139

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. Programming language_sentence_140

Statically typed languages can be either manifestly typed or type-inferred. Programming language_sentence_141

In the first case, the programmer must explicitly write types at certain textual positions (for example, at variable declarations). Programming language_sentence_142

In the second case, the compiler infers the types of expressions and declarations based on context. Programming language_sentence_143

Most mainstream statically typed languages, such as C++, C# and Java, are manifestly typed. Programming language_sentence_144

Complete type inference has traditionally been associated with less mainstream languages, such as Haskell and ML. Programming language_sentence_145

However, many manifestly typed languages support partial type inference; for example, C++, Java and C# all infer types in certain limited cases. Programming language_sentence_146

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. Programming language_sentence_147

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. Programming language_sentence_148

As with type-inferred languages, dynamically typed languages do not require the programmer to write explicit type annotations on expressions. Programming language_sentence_149

Among other things, this may permit a single variable to refer to values of different types at different points in the program execution. Programming language_sentence_150

However, type errors cannot be automatically detected until a piece of code is actually executed, potentially making debugging more difficult. Programming language_sentence_151

Lisp, Smalltalk, Perl, Python, JavaScript, and Ruby are all examples of dynamically typed languages. Programming language_sentence_152

Weak and strong typing Programming language_section_13

Weak typing allows a value of one type to be treated as another, for example treating a string as a number. Programming language_sentence_153

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. Programming language_sentence_154

Strong typing prevents these program faults. Programming language_sentence_155

An attempt to perform an operation on the wrong type of value raises an error. Programming language_sentence_156

Strongly typed languages are often termed type-safe or safe. Programming language_sentence_157

An alternative definition for "weakly typed" refers to languages, such as Perl and JavaScript, which permit a large number of implicit type conversions. Programming language_sentence_158

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. Programming language_sentence_159

Such implicit conversions are often useful, but they can mask programming errors. Programming language_sentence_160

Strong and static are now generally considered orthogonal concepts, but usage in the literature differs. Programming language_sentence_161

Some use the term strongly typed to mean strongly, statically typed, or, even more confusingly, to mean simply statically typed. Programming language_sentence_162

Thus C has been called both strongly typed and weakly, statically typed. Programming language_sentence_163

It may seem odd to some professional programmers that C could be "weakly, statically typed". Programming language_sentence_164

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. Programming language_sentence_165

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). Programming language_sentence_166

Standard library and run-time system Programming language_section_14

Main article: Standard library Programming language_sentence_167

Most programming languages have an associated core 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. Programming language_sentence_168

Core libraries typically include definitions for commonly used algorithms, data structures, and mechanisms for input and output. Programming language_sentence_169

The line between a language and its core library differs from language to language. Programming language_sentence_170

In some cases, the language designers may treat the library as a separate entity from the language. Programming language_sentence_171

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. Programming language_sentence_172

Indeed, some languages are designed so that the meanings of certain syntactic constructs cannot even be described without referring to the core library. Programming language_sentence_173

For example, in Java, 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. Programming language_sentence_174

Conversely, 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. Programming language_sentence_175

Design and implementation Programming language_section_15

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. Programming language_sentence_176

But as artificial constructs, they also differ in fundamental ways from languages that have evolved through usage. Programming language_sentence_177

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. Programming language_sentence_178

By contrast, natural languages have changing meanings given by their users in different communities. Programming language_sentence_179

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. Programming language_sentence_180

Many programming languages have been designed from scratch, altered to meet new needs, and combined with other languages. Programming language_sentence_181

Many have eventually fallen into disuse. Programming language_sentence_182

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. Programming language_sentence_183

The need for diverse programming languages arises from the diversity of contexts in which languages are used: Programming language_sentence_184

Programming language_unordered_list_4

  • Programs range from tiny scripts written by individual hobbyists to huge systems written by hundreds of programmers.Programming language_item_4_17
  • Programmers range in expertise from novices who need simplicity above all else to experts who may be comfortable with considerable complexity.Programming language_item_4_18
  • Programs must balance speed, size, and simplicity on systems ranging from microcontrollers to supercomputers.Programming language_item_4_19
  • Programs may be written once and not change for generations, or they may undergo continual modification.Programming language_item_4_20
  • Programmers may simply differ in their tastes: they may be accustomed to discussing problems and expressing them in a particular language.Programming language_item_4_21

One common trend in the development of programming languages has been to add more ability to solve problems using a higher level of abstraction. Programming language_sentence_185

The earliest programming languages were tied very closely to the underlying hardware of the computer. Programming language_sentence_186

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. Programming language_sentence_187

Because programmers are less tied to the complexity of the computer, their programs can do more computing with less effort from the programmer. Programming language_sentence_188

This lets them write more functionality per time unit. Programming language_sentence_189

Natural language programming has been proposed as a way to eliminate the need for a specialized language for programming. Programming language_sentence_190

However, this goal remains distant and its benefits are open to debate. Programming language_sentence_191

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". Programming language_sentence_192

Alan Perlis was similarly dismissive of the idea. Programming language_sentence_193

Hybrid approaches have been taken in Structured English and SQL. Programming language_sentence_194

A language's designers and users must construct a number of artifacts that govern and enable the practice of programming. Programming language_sentence_195

The most important of these artifacts are the language specification and implementation. Programming language_sentence_196

Specification Programming language_section_16

Main article: Programming language specification Programming language_sentence_197

The specification of a programming language is an artifact that the language users and the implementors can use to agree upon whether a piece of source code is a valid program in that language, and if so what its behavior shall be. Programming language_sentence_198

A programming language specification can take several forms, including the following: Programming language_sentence_199

Programming language_unordered_list_5

  • 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), or a formal semantics (e.g., as in Standard ML and Scheme specifications).Programming language_item_5_22
  • A description of the behavior of a translator for the language (e.g., the 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.Programming language_item_5_23
  • A reference or model implementation, sometimes written in the language being specified (e.g., Prolog or ANSI REXX). The syntax and semantics of the language are explicit in the behavior of the reference implementation.Programming language_item_5_24

Implementation Programming language_section_17

Main article: Programming language implementation Programming language_sentence_200

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. Programming language_sentence_201

There are, broadly, two approaches to programming language implementation: compilation and interpretation. Programming language_sentence_202

It is generally possible to implement a language using either technique. Programming language_sentence_203

The output of a compiler may be executed by hardware or a program called an interpreter. Programming language_sentence_204

In some implementations that make use of the interpreter approach there is no distinct boundary between compiling and interpreting. Programming language_sentence_205

For instance, some implementations of BASIC compile and then execute the source a line at a time. Programming language_sentence_206

Programs that are executed directly on the hardware usually run much faster than those that are interpreted in software. Programming language_sentence_207

One technique for improving the performance of interpreted programs is just-in-time compilation. Programming language_sentence_208

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. Programming language_sentence_209

Proprietary languages Programming language_section_18

Use Programming language_section_19

Thousands of different programming languages have been created, mainly in the computing field. Programming language_sentence_210

Individual software projects commonly use five programming languages or more. Programming language_sentence_211

Programming languages differ from most other forms of human expression in that they require a greater degree of precision and completeness. Programming language_sentence_212

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. Programming language_sentence_213

However, figuratively speaking, computers "do exactly what they are told to do", and cannot "understand" what code the programmer intended to write. Programming language_sentence_214

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. Programming language_sentence_215

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. Programming language_sentence_216

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. Programming language_sentence_217

A programmer uses the abstractions present in the language to represent the concepts involved in a computation. Programming language_sentence_218

These concepts are represented as a collection of the simplest elements available (called primitives). Programming language_sentence_219

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. Programming language_sentence_220

Programs for a computer might be executed in a batch process without human interaction, or a user might type commands in an interactive session of an interpreter. Programming language_sentence_221

In this case the "commands" are simply programs, whose execution is chained together. Programming language_sentence_222

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. Programming language_sentence_223

Measuring language usage Programming language_section_20

Main article: Measuring programming language popularity Programming language_sentence_224

Determining which is the most widely used programming language is difficult since the definition of usage varies by context. Programming language_sentence_225

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. Programming language_sentence_226

Some languages are very popular for particular kinds of applications. Programming language_sentence_227

For example, COBOL is still strong in the corporate data center, often on large mainframes; Fortran in scientific and engineering applications; Ada in aerospace, transportation, military, real-time and embedded applications; and C in embedded applications and operating systems. Programming language_sentence_228

Other languages are regularly used to write many different kinds of applications. Programming language_sentence_229

Various methods of measuring language popularity, each subject to a different bias over what is measured, have been proposed: Programming language_sentence_230

Programming language_unordered_list_6

  • counting the number of job advertisements that mention the languageProgramming language_item_6_25
  • the number of books sold that teach or describe the languageProgramming language_item_6_26
  • estimates of the number of existing lines of code written in the language – which may underestimate languages not often found in public searchesProgramming language_item_6_27
  • counts of language references (i.e., to the name of the language) found using a web search engine.Programming language_item_6_28

Combining and averaging information from various internet sites, reported the ten most popular programming languages as (in descending order by overall popularity): Java, C, C++, Python, C#, JavaScript, VB .NET, R, PHP, and MATLAB. Programming language_sentence_231

Dialects, flavors and implementations Programming language_section_21

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. Programming language_sentence_232

With languages such as Scheme and Forth, standards may be considered insufficient, inadequate or illegitimate by implementors, so often they will deviate from the standard, making a new dialect. Programming language_sentence_233

In other cases, a dialect is created for use in a domain-specific language, often a subset. Programming language_sentence_234

In the 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 and Clojure. Programming language_sentence_235

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. Programming language_sentence_236

The BASIC programming language has many dialects. Programming language_sentence_237

The explosion of Forth dialects led to the saying "If you've seen one Forth... you've seen one Forth." Programming language_sentence_238

Taxonomies Programming language_section_22

Further information: Categorical list of programming languages Programming language_sentence_239

There is no overarching classification scheme for programming languages. Programming language_sentence_240

A given programming language does not usually have a single ancestor language. Programming language_sentence_241

Languages commonly arise by combining the elements of several predecessor languages with new ideas in circulation at the time. Programming language_sentence_242

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. Programming language_sentence_243

The task is further complicated by the fact that languages can be classified along multiple axes. Programming language_sentence_244

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). Programming language_sentence_245

Python is an object-oriented scripting language. Programming language_sentence_246

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. Programming language_sentence_247

Traditionally, programming languages have been regarded as describing computation in terms of imperative sentences, i.e. issuing commands. Programming language_sentence_248

These are generally called imperative programming languages. Programming language_sentence_249

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. Programming language_sentence_250

More refined paradigms include procedural programming, object-oriented programming, functional programming, and logic programming; some languages are hybrids of paradigms or multi-paradigmatic. Programming language_sentence_251

An assembly language is not so much a paradigm as a direct model of an underlying machine architecture. Programming language_sentence_252

By purpose, programming languages might be considered general purpose, system programming languages, scripting languages, domain-specific languages, or concurrent/distributed languages (or a combination of these). Programming language_sentence_253

Some general purpose languages were designed largely with educational goals. Programming language_sentence_254

A programming language may also be classified by factors unrelated to programming paradigm. Programming language_sentence_255

For instance, most programming languages use English language keywords, while a minority do not. Programming language_sentence_256

Other languages may be classified as being deliberately esoteric or not. Programming language_sentence_257

See also Programming language_section_23

Credits to the contents of this page go to the authors of the corresponding Wikipedia page: language.