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Pascal

Pascal is an imperative and procedural programming language, designed by Niklaus Wirth as a small, efficient language intended to encourage good programming practices using structured programming and data structuring. It is named in honour of the French mathematician, philosopher and physicist Blaise Pascal.

Based on Wirth’s book, Algorithms + Data Structures = Programs, Pascal was developed on the pattern of the ALGOL 60 language. Wirth was involved in the process to improve the language as part of the ALGOL X efforts and proposed a version known as ALGOL W. This was not accepted, and the ALGOL X process bogged down. In 1968, Wirth decided to abandon the ALGOL X process and further improve ALGOL W, releasing this as Pascal in 1970.

On top of ALGOL’s scalars and arrays, Pascal enabled defining complex datatypes and building dynamic and recursive data structures such as lists, trees and graphs. Pascal has strong typing on all objects, which means that one type of data cannot be converted or interpreted as another without explicit conversions. Unlike most languages in the C-family, Pascal allows nested procedure definitions to any level of depth, and also allows most kinds of definitions and declarations inside subroutines (procedures and functions). A program is thus syntactically similar to a single procedure or function.

Pascal became very successful in the 1970s, notably on the burgeoning minicomputer market. Compilers were also available for many microcomputers as the field emerged in the late 1970s. It was widely used as a teaching language in university-level programming courses in the 1980s, and also used in production settings for writing commercial software during the same period. It was displaced by the C programming language during the late 1980s and early 1990s as UNIX-based systems became popular, and especially with the release of C++.

A derivative known as Object Pascal designed for object-oriented programming was developed in 1985; this was used by Apple Computer and Borland in the late 1980s and later developed into Delphi on the Microsoft Windows platform. Extensions to the Pascal concepts led to the languages Modula-2 and Oberon.

History

Earlier efforts

Much of the history of computer language design during the 1960s can be traced to the ALGOL 60 language. ALGOL was developed during the 1950s with the explicit goal to be able to clearly describe algorithms. It included a number of features for structured programming that remain common in languages to this day.

Shortly after its introduction, in 1962 Wirth began working on his dissertation with Helmut Weber on the Euler programming language. Euler was based on ALGOL’s syntax and many concepts but was not a derivative. Its primary goal was to add dynamic lists and types, allowing it to be used in roles similar to Lisp. The language was published in 1965.

By this time, a number of problems in ALGOL had been identified, notably the lack of a standardized string system. The group tasked with maintaining the language had begun the ALGOL X process to identify improvements, calling for submissions. Wirth and Tony Hoare submitted a conservative set of modifications to add strings and clean up some of the syntax. These were considered too minor to be worth using as the new standard ALGOL, so Wirth wrote a compiler for the language, which became known as ALGOL W.

The ALGOL X efforts would go on to choose a much more complex language, ALGOL 68. The complexity of this language led to considerable difficulty producing high-performance compilers, and it was not widely used in the industry. This left an opening for newer languages.

Pascal

Pascal was influenced by the ALGOL W efforts, with the explicit goals of producing a language that would be efficient both in the compiler and at run-time, allow for the development of well-structured programs, and to be useful for teaching students structured programming.[4] A generation of students used Pascal as an introductory language in undergraduate courses.

One of the early successes for the language was the introduction of UCSD Pascal, a version that ran on a custom operating system that could be ported to different platforms. A key platform was the Apple II, where it saw widespread use. This led to the use of Pascal becoming the primary high-level language used for development in the Apple Lisa, and later, the Macintosh. Parts of the original Macintosh operating system were hand-translated into Motorola 68000 assembly language from the Pascal sources.[5]

The typesetting system TeX by Donald E. Knuth was written in WEB, the original literate programming system, based on DEC PDP-10 Pascal. Successful commercial applications like Adobe Photoshop[6] were written in Macintosh Programmer’s Workshop Pascal, while applications like Total Commander, Skype[citation needed] and Macromedia Captivate were written in Delphi (Object Pascal). Apollo Computer used Pascal as the systems programming language for its operating systems beginning in 1980.

Variants of Pascal have also been used for everything from research projects to PC games and embedded systems. Newer Pascal compilers exist which are widely used.[7]

Object Pascal

During work on the Lisa, Larry Tesler began corresponding with Wirth on the idea of adding object oriented extensions to the language. This led initially to Clascal, introduced in 1983. As the Lisa program faded and was replaced by the Mac, a further version known as Object Pascal was created. This was introduced on the Macintosh in 1985 as part of the MacApp application framework, and became Apple’s primary development language into the early 1990s.

The Object Pascal extensions were added to Turbo Pascal with the release of version 5.5 in 1989.[8] Over the years, Object Pascal became the basis of the Delphi system for Microsoft Windows, which is still used for developing Windows applications, and can cross-compile code to other systems. Free Pascal is an open source, cross-platform alternative.

Implementations

Early Pascal compilers

The first Pascal compiler was designed in Zürich for the CDC 6000 series mainframe computer family. Niklaus Wirth reports that a first attempt to implement it in Fortran in 1969 was unsuccessful due to Fortran’s inadequacy to express complex data structures. The second attempt was implemented in a C-like language (Scallop by Max Engeli) and then translated by hand (by R. Schild) to Pascal itself for boot-strapping.[9] It was operational by mid-1970. Many Pascal compilers since have been similarly self-hosting, that is, the compiler is itself written in Pascal, and the compiler is usually capable of recompiling itself when new features are added to the language, or when the compiler is to be ported to a new environment. The GNU Pascal compiler is one notable exception, being written in C.

The first successful port of the CDC Pascal compiler to another mainframe was completed by Welsh and Quinn at the Queen’s University of Belfast (QUB) in 1972. The target was the ICL 1900 series. This compiler, in turn, was the parent of the Pascal compiler for the Information Computer Systems (ICS) Multum minicomputer. The Multum port was developed – with a view to using Pascal as a systems programming language – by Findlay, Cupples, Cavouras and Davis, working at the Department of Computing Science in Glasgow University. It is thought that Multum Pascal, which was completed in the summer of 1973, may have been the first 16-bit implementation.

A completely new compiler was completed by Welsh et al. at QUB in 1977. It offered a source-language diagnostic feature (incorporating profiling, tracing and type-aware formatted postmortem dumps) that was implemented by Findlay and Watt at Glasgow University. This implementation was ported in 1980 to the ICL 2900 series by a team based at Southampton University and Glasgow University. The Standard Pascal Model Implementation was also based on this compiler, having been adapted, by Welsh and Hay at Manchester University in 1984, to check rigorously for conformity to the BSI 6192/ISO 7185 Standard and to generate code for a portable abstract machine.

The first Pascal compiler written in North America was constructed at the University of Illinois under Donald B. Gillies for the PDP-11 and generated native machine code.

The Pascal-P system

To propagate the language rapidly, a compiler porting kit was created in Zürich that included a compiler that generated so called p-code for a virtual stack machine, i.e., code that lends itself to reasonably efficient interpretation, along with an interpreter for that code – the Pascal-P system. The P-system compilers were named Pascal-P1, Pascal-P2, Pascal-P3, and Pascal-P4. Pascal-P1 was the first version, and Pascal-P4 was the last to come from Zürich. The version termed Pascal-P1 was coined after the fact for the many different sources for Pascal-P that existed. The compiler was redesigned to enhance portability, and issued as Pascal-P2. This code was later enhanced to become Pascal-P3, with an intermediate code backward compatible with Pascal-P2, and Pascal-P4, which was not backward compatible.

The Pascal-P4 compiler–interpreter can still be run and compiled on systems compatible with original Pascal. However, it only accepts a subset of the Pascal language.

Pascal-P5, created outside the Zürich group, accepts the full Pascal language and includes ISO 7185 compatibility.

UCSD Pascal branched off Pascal-P2, where Kenneth Bowles used it to create the interpretive UCSD p-System. It was one of three operating systems available at the launch of the original IBM Personal Computer.[10] UCSD Pascal used an intermediate code based on byte values, and thus was one of the earliest byte code compilers. Pascal-P1 through Pascal-P4 was not, but rather based on the CDC 6600 60-bit word length.

A compiler based on the Pascal-P4 compiler, which created native binaries, was released for the IBM System/370 mainframe computer by the Australian Atomic Energy Commission; it was named the AAEC Pascal Compiler after the abbreviation of the name of the commission.[11]

Object Pascal and Turbo Pascal

Apple Computer created its own Lisa Pascal for the Lisa Workshop in 1982, and ported the compiler to the Apple Macintosh and MPW in 1985. In 1985 Larry Tesler, in consultation with Niklaus Wirth, defined Object Pascal and these extensions were incorporated in both the Lisa Pascal and Mac Pascal compilers.

In the 1980s, Anders Hejlsberg wrote the Blue Label Pascal compiler for the Nascom-2. A reimplementation of this compiler for the IBM PC was marketed under the names Compas Pascal and PolyPascal before it was acquired by Borland and renamed Turbo Pascal.

Turbo Pascal became hugely popular, thanks to an aggressive pricing strategy, having one of the first full-screen IDEs, and very fast turnaround time (just seconds to compile, link, and run). It was written and highly optimized entirely in assembly language, making it smaller and faster than much of the competition.

In 1986, Anders ported Turbo Pascal to the Macintosh and incorporated Apple’s Object Pascal extensions into Turbo Pascal. These extensions were then added back into the PC version of Turbo Pascal for version 5.5. At the same time Microsoft also implemented the Object Pascal compiler.[12][13] Turbo Pascal 5.5 had a large influence on the Pascal community, which began concentrating mainly on the IBM PC in the late 1980s. Many PC hobbyists in search of a structured replacement for BASIC used this product. It also began to be adopted by professional developers. Around the same time a number of concepts were imported from C to let Pascal programmers use the C-based API of Microsoft Windows directly. These extensions included null-terminated strings, pointer arithmetic, function pointers, an address-of operator and unsafe typecasts.

Turbo Pascal, and other derivatives with units or module concepts are modular languages. However, it does not provide a nested module concept or qualified import and export of specific symbols.

Other variants

Super Pascal is a variant that added non-numeric labels, a return statement and expressions as names of types.

TMT Pascal was the first Borland-compatible compiler for 32-bit DOS protected mode, OS/2 and Win32 operating systems. The TMT Pascal language was the first one to allow function and operator overloading.

The universities of Wisconsin-Madison, Zürich, Karlsruhe and Wuppertal developed the Pascal-SC[14][15] and Pascal-XSC[16][17][18] (Extensions for Scientific Computation) compilers, aimed at programming numerical computations. Development for Pascal-SC started in 1978 supporting ISO 7185 Pascal level 0, but level 2 support was added at a later stage.[19] Pascal-SC originally targeted the Z80 processor, but was later rewritten for DOS (x86) and 68000. Pascal-XSC has at various times been ported to Unix (Linux, SunOS, HP-UX, AIX) and Microsoft/IBM (DOS with EMX, OS/2, Windows) operating systems. It operates by generating intermediate C source code which is then compiled to a native executable. Some of the Pascal-SC language extensions have been adopted by GNU Pascal.

Pascal Sol was designed around 1983 by a French team to implement a Unix-like systems named Sol. It was standard Pascal level-1 (with parametrized array bounds) but the definition allowed alternative keywords and predefined identifiers in French and the language included a few extensions to ease system programming (e.g. an equivalent to lseek).[20] The Sol team later on moved to the ChorusOS project to design a distributed operating system.[21]

IP Pascal was an implementation of the Pascal programming language using Micropolis DOS, but was moved rapidly to CP/M-80 running on the Z80. It was moved to the 80386 machine types in 1994, and exists today as Windows/XP and Linux implementations. In 2008, the system was brought up to a new level and the resulting language termed “Pascaline” (after Pascal’s calculator). It includes objects, namespace controls, dynamic arrays, along with many other extensions, and generally features the same functionality and type protection as C#. It is the only such implementation that is also compatible with the original Pascal implementation, which is standardized as ISO 7185.

Language constructs

Pascal, in its original form, is a purely procedural language and includes the traditional array of ALGOL-like control structures with reserved words such as if, then, else, while, for, and case ranging on a single statement or a beginend statements block. Pascal also has data structuring constructs not included in the original ALGOL 60 types, like records, variants, pointers, enumerations, and sets and procedure/pointers. Such constructs were in part inherited or inspired from Simula 67, ALGOL 68, Niklaus Wirth‘s own ALGOL W and suggestions by C. A. R. Hoare.

Pascal programs start with the program keyword with a list of external file descriptors as parameters[22] (not required in Turbo Pascal etc.); then follows the main block bracketed by the begin and end keywords. Semicolons separate statements, and the full stop (i.e., a period) ends the whole program (or unit). Letter case is ignored in Pascal source.

Here is an example of the source code in use for a very simple “Hello, World!” program:

program HelloWorld(output);
begin
    Write('Hello, World!')
    {No ";" is required after the last statement of a block -
        adding one adds a "null statement" to the program, which is ignored by the compiler.}
end.

Data types

A type in Pascal, and in several other popular programming languages, defines a variable in such a way that it defines a range of values which the variable is capable of storing, and it also defines a set of operations that are permissible to be performed on variables of that type. The predefined types are:

Data type Type of values which the variable is capable of storing
integer integer (whole) numbers
real floating-point numbers
boolean the values True or False
char a single character from an ordered character set
string a sequence or “string” of characters
set equivalent to an array of boolean values

The range of values allowed for each (except boolean) is implementation defined. Functions are provided for some data conversions. For conversion of real to integer, the following functions are available: round (which rounds to integer using banker’s rounding) and trunc (rounds towards zero).

The programmer has the freedom to define other commonly used data types (e.g. byte, string, etc.) in terms of the predefined types using Pascal’s type declaration facility, for example

type
    byte        = 0..255;
    signed_byte = -128..127;
    string      = packed array[1..255] of char;

(Often-used types like byte and string are already defined in many implementations.)

Subrange types

Subranges of any ordinal data type (any simple type except real) can also be made:

var
    x : 1..10;
    y : 'a'..'z';

Set types

In contrast with other programming languages from its time, Pascal supports a set type:[23]

var
    Set1 : set of 1..10;
    Set2 : set of 'a'..'z';

A set is a fundamental concept for modern mathematics, and they may be used in many algorithms. Such a feature is useful and may be faster than an equivalent construct in a language that does not support sets. For example, for many Pascal compilers:

if i in [5..10] then ...

executes faster than:

if (i > 4) and (i < 11) then ...

Sets of non-contiguous values can be particularly useful, in terms of both performance and readability:

if i in [0..3, 7, 9, 12..15] then ...

For these examples, which involve sets over small domains, the improved performance is usually achieved by the compiler representing set variables as bit vectors. The set operators can then be implemented efficiently as bitwise machine code operations.

Type declarations

Types can be defined from other types using type declarations:

type
    x = integer;
    y = x;
...

Further, complex types can be constructed from simple types:

type
    a = array[1..10] of integer;
    b = record
        x : integer;
        y : char  {extra semicolon not strictly required}
    end;
    c = file of a;

File type

As shown in the example above, Pascal files are sequences of components. Every file has a buffer variable which is denoted by f^. The procedures get (for reading) and put (for writing) move the buffer variable to the next element. Read is introduced such that read(f, x) is the same as x := f^; get(f);. Write is introduced such that write(f, x) is the same as f^ := x; put(f); The type text is predefined as file of char. While the buffer variable could be used for inspecting the next character to be used (check for a digit before reading an integer), this leads to serious problems with interactive programs in early implementations, but was solved later with the “lazy I/O” concept.

In Jensen & Wirth Pascal, strings are represented as packed arrays of chars; they therefore have fixed length and are usually space-padded.

Pointer types

Pascal supports the use of pointers:

type
    pNode = ^Node;
    Node  = record
        a : integer;
        b : char;
        c : pNode  
    end;
var
    NodePtr : pNode;
    IntPtr  : ^integer;

Here the variable NodePtr is a pointer to the data type Node, a record. Pointers can be used before they are declared. This is a forward declaration, an exception to the rule that things must be declared before they are used.

To create a new record and assign the value 10 and character A to the fields a and b in the record, and to initialise the pointer c to the null pointer (“NIL” in Pascal), the statements would be:

New(NodePtr);
...
NodePtr^.a := 10;
NodePtr^.b := 'A';
NodePtr^.c := NIL;
...

This could also be done using the with statement, as follows:

New(NodePtr);
...
with NodePtr^ do
begin
    a := 10;
    b := 'A';
    c := NIL
end;
...

Inside of the scope of the with statement, a and b refer to the subfields of the record pointer NodePtr and not to the record Node or the pointer type pNode.

Linked lists, stacks and queues can be created by including a pointer type field (c) in the record.

Unlike many languages that feature pointers, Pascal only allows pointers to reference dynamically created variables that are anonymous, and does not allow them to reference standard static or local variables. Pointers also must have an associated type, and a pointer to one type is not compatible with a pointer to another type (e.g. a pointer to a char is not compatible with a pointer to an integer). This helps eliminate the type security issues inherent with other pointer implementations, particularly those used for PL/I or C. It also removes some risks caused by dangling pointers, but the ability to dynamically deallocate referenced space by using the dispose function (which has the same effect as the free library function found in C) means that the risk of dangling pointers has not been entirely eliminated[24] as it has in languages such as Java and C#, which provide automatic garbage collection (but which do not entirely eliminate the related problem of memory leaks).

Some of these restrictions can be lifted in newer dialects.

Control structures

Pascal is a structured programming language, meaning that the flow of control is structured into standard statements, usually without ‘goto‘ commands.

while a <> b do  WriteLn('Waiting');

if a > b then WriteLn('Condition met')   {no semicolon allowed!}
    else WriteLn('Condition not met');

for i := 1 to 10 do  {no semicolon for single statements allowed!}
    WriteLn('Iteration: ', i);

repeat
    a := a + 1
until a = 10;

case i of
    0 : Write('zero');
    1 : Write('one');
    2 : Write('two');
    3,4,5,6,7,8,9,10: Write('?')
end;

Procedures and functions

Pascal structures programs into procedures and functions.

program Printing;

var i : integer;

procedure Print(j : integer);
begin
    ...
end;

begin { main program }
    ...
    Print(i);
end.

Procedures and functions can be nested to any depth, and the ‘program’ construct is the logical outermost block.

By default, parameters are passed by value. If ‘var’ precedes a parameter’s name, it is passed by reference.

Each procedure or function can have its own declarations of goto labels, constants, types, variables, and other procedures and functions, which must all be in that order.
This ordering requirement was originally intended to allow efficient single-pass compilation. However, in some dialects (such as Embarcadero Delphi) the strict ordering requirement of declaration sections has been relaxed.

Semicolons as statement separators

Pascal adopted many language syntax features from the ALGOL language, including the use of a semicolon as a statement separator. This is in contrast to other languages, such as PL/I, C etc. which use the semicolon as a statement terminator. No semicolon is needed before the end keyword of a record type declaration, a block, or a case statement; before the until keyword of a repeat statement; and before the else keyword of an if statement.

The presence of an extra semicolon was not permitted in early versions of Pascal. However, the addition of ALGOL-like empty statements in the 1973 Revised Report and later changes to the language in ISO 7185:1983 now allow for optional semicolons in most of these cases. A semicolon is still not permitted immediately before the else keyword in an if statement, because the else follows a single statement, not a statement sequence. In the case of nested ifs, a semicolon cannot be used to avoid the dangling else problem (where the inner if does not have an else, but the outer if does) by putatively terminating the nested if with a semicolon – this instead terminates both if clauses. Instead, an explicit begin...end block must be used.[25]

Resources

Compilers and interpreters

Several Pascal compilers and interpreters are available for general use:

  • Delphi is Embarcadero’s (formerly Borland/CodeGear) flagship rapid application development (RAD) product. It uses the Object Pascal language (termed ‘Delphi’ by Borland), descended from Pascal, to create applications for Windows, macOS, iOS, and Android. The .NET support that existed from D8 through D2005, D2006 and D2007 has been terminated, and replaced by a new language (Prism, which is rebranded Oxygene, see below) that is not fully backward compatible. In recent years Unicode support and generics were added (D2009, D2010, Delphi XE).
  • Free Pascal is a multi-platform compiler written in Object Pascal (and is self-hosting). It is aimed at providing a convenient and powerful compiler, both able to compile legacy applications and to be the means of developing new ones. It is distributed under the GNU GPL, while packages and runtime library come under a modified GNU LGPL. Apart from compatibility modes for Turbo Pascal, Delphi and Mac Pascal, it also has its own procedural and object-oriented syntax modes with support for extended features such as operator overloading. It supports many platforms and operating systems. Current versions also feature an ISO mode.
  • Modern Pascal is a multi-platform interpreter and p-code compiler written in Free Pascal. It is aimed at providing alternative solutions for PHP and node.js, using either an ISO standard pascal dialect or a hybrid supporting JavaScript/C operators. From the CLI it is useful as a Free Pascal interpreter.
  • Turbo51 is a free Pascal compiler for the 8051 family of microcontrollers, with Turbo Pascal 7 syntax.
  • Oxygene (formerly known as Chrome) is an Object Pascal compiler for the .NET and Mono platforms. It was created and is sold by RemObjects Software, and sold for a while by Embarcadero as the backend compiler of Prism.
  • Kylix was a descendant of Delphi, with support for the Linux operating system and an improved object library. It is no longer supported. Compiler and IDE are available now for non-commercial use.
  • GNU Pascal Compiler (GPC) is the Pascal compiler of the GNU Compiler Collection (GCC). The compiler itself is written in C, the runtime library mostly in Pascal. Distributed under the GNU General Public License, it runs on many platforms and operating systems. It supports the ANSI/ISO standard languages and has partial Turbo Pascal dialect support. One of the more painful omissions is the absence of a 100% Turbo Pascal-compatible (short)string type. Support for Borland Delphi and other language variations is quite limited. There is some support for Mac-pascal however.
  • Virtual Pascal was created by Vitaly Miryanov in 1995 as a native OS/2 compiler compatible with Borland Pascal syntax. Then, it had been commercially developed by fPrint, adding Win32 support, and in 2000 it became freeware. Today it can compile for Win32, OS/2 and Linux, and is mostly compatible with Borland Pascal and Delphi. Development was canceled on April 4, 2005.
  • P4 compiler, the basis for many subsequent Pascal-implemented-in-Pascal compilers. It implements a subset of full Pascal.
  • P5 compiler, is an ISO 7185 (full Pascal) adaption of P4.
  • Smart Mobile Studio is a Pascal to HTML5/Javascript compiler
  • Turbo Pascal was the dominant Pascal compiler for PCs during the 1980s and early 1990s, popular both because of its powerful extensions and extremely short compilation times. Turbo Pascal was compactly written and could compile, run, and debug all from memory without accessing disk. Slow floppy disk drives were common for programmers at the time, further magnifying Turbo Pascal’s speed advantage. Currently, older versions of Turbo Pascal (up to 5.5) are available for free download from Borland’s site.
  • IP Pascal Implements the language “Pascaline” (named after Pascal’s calculator), which is a highly extended Pascal compatible with original Pascal according to ISO 7185. It features modules with namespace control, including parallel tasking modules with semaphores, objects, dynamic arrays of any dimensions that are allocated at runtime, overloads, overrides, and many other extensions. IP Pascal has a built-in portability library that is custom tailored to the Pascal language. For example, a standard text output application from 1970’s original Pascal can be recompiled to work in a window and even have graphical constructs added.
  • Pascal-XT was created by Siemens for their mainframe operating systems BS2000 and SINIX.
  • PocketStudio is a Pascal subset compiler and RAD tool for Palm OS and MC68xxx processors with some own extensions to assist interfacing with the Palm OS API. It resembles Delphi and Lazarus with a visual form designer, an object inspector and a source code editor.
  • MIDletPascal – A Pascal compiler and IDE that generates small and fast Java bytecode specifically designed to create software for mobiles
  • Vector Pascal is a language for SIMD instruction sets such as the MMX and the AMD 3d Now, supporting all Intel and AMD processors, and Sony’s PlayStation 2 Emotion Engine.
  • Morfik Pascal allows the development of Web applications entirely written in Object Pascal (both server and browser side).
  • WDSibyl – Visual Development Environment and Pascal compiler for Win32 and OS/2
  • PP Compiler, a compiler for Palm OS that runs directly on the handheld computer.
  • CDC 6000 Pascal compiler is the source code for the first (CDC 6000) Pascal compiler.
  • Pascal-S[26]
  • AmigaPascal is a free Pascal compiler for the Amiga computer.
  • VSI Pascal (originally VAX Pascal) is an ISO Standard Pascal compliant compiler for the OpenVMS operating system.

IDEs

Libraries

  • WOL Library for creating GUI applications with the Free Pascal Compiler.

Standards

ISO/IEC 7185:1990 Pascal

In 1983, the language was standardized, in the international standard IEC/ISO 7185,[27] and several local country specific standards, including the American ANSI/IEEE770X3.97-1983, and ISO 7185:1983. These two standards differed only in that the ISO standard included a “level 1” extension for conformant arrays (an array where the boundaries of the array are not known until run time), where ANSI did not allow for this extension to the original (Wirth version) language. In 1989, ISO 7185 was revised (ISO 7185:1990) to correct various errors and ambiguities found in the original document.

The ISO 7185 was stated to be a clarification of Wirth’s 1974 language as detailed by the User Manual and Report [Jensen and Wirth], but was also notable for adding “Conformant Array Parameters” as a level 1 to the standard, level 0 being Pascal without conformant arrays. This addition was made at the request of C. A. R. Hoare, and with the approval of Niklaus Wirth. The precipitating cause was that Hoare wanted to create a Pascal version of the (NAG) Numerical Algorithms Library, which had originally been written in FORTRAN, and found that it was not possible to do so without an extension that would allow array parameters of varying size. Similar considerations motivated the inclusion in ISO 7185 of the facility to specify the parameter types of procedural and functional parameters.

Niklaus Wirth himself referred to the 1974 language as “the Standard”, for example, to differentiate it from the machine specific features of the CDC 6000 compiler. This language was documented in The Pascal Report,[28] the second part of the “Pascal users manual and report”.

On the large machines (mainframes and minicomputers) Pascal originated on, the standards were generally followed. On the IBM PC, they were not. On IBM PCs, the Borland standards Turbo Pascal and Delphi have the greatest number of users. Thus, it is typically important to understand whether a particular implementation corresponds to the original Pascal language, or a Borland dialect of it.

The IBM PC versions of the language began to differ with the advent of UCSD Pascal, an interpreted implementation that featured several extensions to the language, along with several omissions and changes. Many UCSD language features survive today, including in Borland’s dialect.

ISO/IEC 10206:1990 Extended Pascal

In 1990, an extended Pascal standard was created as ISO/IEC 10206,[29] which is identical in technical content[30] to IEEE/ANSI 770X3.160-1989[31]
As of 2019, Support of Extended Pascal in FreePascal Compiler is planned.[32]

Variations

Niklaus Wirth’s Zürich version of Pascal was issued outside ETH in two basic forms, the CDC 6000 compiler source, and a porting kit called Pascal-P system. The Pascal-P compiler left out several features of the full language that were not required to bootstrap the compiler. For example, procedures and functions used as parameters, undiscriminated variant records, packing, dispose, interprocedural gotos and other features of the full compiler were omitted.

UCSD Pascal, under Professor Kenneth Bowles, was based on the Pascal-P2 kit, and consequently shared several of the Pascal-P language restrictions. UCSD Pascal was later adopted as Apple Pascal, and continued through several versions there. Although UCSD Pascal actually expanded the subset Pascal in the Pascal-P kit by adding back standard Pascal constructs, it was still not a complete standard installation of Pascal.

In the early 1990s, Alan Burns and Geoff Davies developed Pascal-FC, an extension to Pl/0 (from the Niklaus’ book ‘Algorithms+Data Structures=Programs’). Several constructs were added to use Pascal-FC as a teaching tool for Concurrent Programming (such as semaphores, monitors, channels, remote-invocation and resources). To be able to demonstrate concurrency, the compiler output (a kind of P-code) could then be executed on a virtual machine. This virtual machine not only simulated a normal – fair – environment, but could also simulate extreme conditions (unfair mode).

Borland-like Pascal compilers

Borland‘s Turbo Pascal, written by Anders Hejlsberg, was written in assembly language independent of UCSD or the Zürich compilers. However, it adopted much of the same subset and extensions as the UCSD compiler. This is probably because the UCSD system was the most common Pascal system suitable for developing applications on the resource-limited microprocessor systems available at that time.

The shrink-wrapped Turbo Pascal version 3 and later incarnations, including Borland’s Object Pascal and Delphi and non-Borland near-compatibles became popular with programmers including shareware authors, and so the SWAG library of Pascal code features a large amount of code written with such versions as Delphi in mind.

Software products (compilers, and IDE/Rapid Application Development (RAD) in this category:

  • Turbo Pascal – “TURBO.EXE” up to version 7, and Turbo Pascal for Windows (“TPW”) and Turbo Pascal for Macintosh.
  • Borland Pascal 7 (essentially Turbo Pascal 7 for Windows).
  • Object Pascal – an extension of the Pascal language that was developed at Apple Computer by a team led by Larry Tesler in consultation with Niklaus Wirth, the inventor of Pascal; its features were added to Borland’s Turbo Pascal for Macintosh and in 1989 for Turbo Pascal 5.5 for DOS.
  • Delphi – Object Pascal is essentially its underlying language.
  • Free Pascal compiler (FPC) – Free Pascal adopted the de facto standard dialect of Pascal programmers, Borland Pascal and, later, Delphi. Freepascal also supports both ISO standards.
  • PascalABC.NET – is a new generation Pascal programming language including compiler and IDE
  • Borland Kylix is a compiler and IDE formerly sold by Borland, but later discontinued. It is a Linux version of the Borland Delphi software development environment and C++Builder.
  • Lazarus – similar to Kylix in function, is a free cross-platform visual IDE for RAD using the Free Pascal compiler, which supports dialects of Object Pascal, to varying degrees.
  • Virtual Pascal – VP2/1 is a fully Borland Pascal and Borland Delphi compatible 32-bit Pascal compiler for OS/2 and Win 32 (with a Linux version “on the way”).[33]
  • Sybil is an open source Delphi-like IDE and compiler; implementations include WDSibyl[34] for Microsoft Windows and OS/2, a commercial Borland Pascal compatible environment released by a company called Speedsoft that was later developed into a Delphi like RAD environment called Sybil and then open sourced under the GPL when that company closed down; Open Sybil is an ongoing project, an Open source Pascal RAD (Rapid Application Development) Tool for OS/2 and eCS that was originally based on Speedsoft’s WDsybl SPCC (Sibyl Portable Component Classes) and SVDE (Sibyl Visual Development Tool) sources but now the core is SOM, WPS and OpenDoc.[35]

List of related standards

  • ISO 8651-2:1988 Information processing systems – Computer graphics – Graphical Kernel System (GKS) language bindings – Part 2: Pascal

Reception

Pascal generated a wide variety of responses in the computing community, both critical and complimentary.

Early criticism

While very popular in the 1980s and early 1990s, implementations of Pascal that closely followed Wirth’s initial definition of the language were widely criticized as being unsuitable for use outside teaching. Brian Kernighan, who popularized the C language, outlined his most notable criticisms of Pascal as early as 1981 in his article “Why Pascal is Not My Favorite Programming Language”.[36] The most serious problem described by him was that array sizes and string lengths were part of the type, so it was not possible to write a function that would accept variable-length arrays or even strings as parameters. This made it unfeasible to write, for example, a sorting library. Kernighan also criticized the unpredictable order of evaluation of boolean expressions, poor library support, and lack of static variables, and raised a number of smaller issues. Also, he stated that the language did not provide any simple constructs to “escape” (knowingly and forcibly ignore) restrictions and limitations. More general complaints from other sources[24][37] noted that the scope of declarations was not clearly defined in the original language definition, which sometimes had serious consequences when using forward declarations to define pointer types, or when record declarations led to mutual recursion, or when an identifier may or may not have been used in an enumeration list. Another difficulty was that, like ALGOL 60, the language did not allow procedures or functions passed as parameters to predefine the expected type of their parameters.

Most of Kernighan’s criticisms were directly addressed in the article “The Pascal Programming Language” by Bill Catambay,[38] specifically, under “Myth 6: Pascal Is Not For Serious Programmers”.[39]

Despite initial criticisms, Pascal continued to evolve, and most of Kernighan’s points do not apply to versions of the language which were enhanced to be suitable for commercial product development, such as Borland’s Turbo Pascal. As Kernighan predicted in his article, most of the extensions to fix these issues were incompatible from compiler to compiler. Since the early 1990s, however, most of the varieties seem condensed into two categories: ISO and Borland-like.

Extended Pascal addresses many of these early criticisms. It supports variable-length strings, variable initialization, separate compilation, short-circuit boolean operators, and default (otherwise) clauses for case statements.[40]

Further reading

  • Niklaus Wirth: The Programming Language Pascal. 35–63, Acta Informatica, Volume 1, 1971.
  • C. A. R. Hoare: “Notes on data structuring”. In O.-J. Dahl, E. W. Dijkstra and C. A. R. Hoare, editors, Structured Programming, pages 83–174. Academic Press, 1972.
  • C. A. R. Hoare, Niklaus Wirth: An Axiomatic Definition of the Programming Language Pascal. 335–355, Acta Informatica, Volume 2, 1973.
  • Kathleen Jensen and Niklaus Wirth: PASCAL – User Manual and Report. Springer-Verlag, 1974, 1985, 1991, ISBN 0-387-97649-3 and ISBN 3-540-97649-3.
  • Niklaus Wirth: Algorithms + Data Structures = Programs. Prentice-Hall, 1975, ISBN 0-13-022418-9.
  • Niklaus Wirth: An assessment of the programming language PASCAL. 23–30 ACM SIGPLAN Notices Volume 10, Issue 6, June 1975.
  • N. Wirth, and A. I. Wasserman, ed: Programming Language Design. IEEE Computer Society Press, 1980
  • D. W. Barron (Ed.): Pascal – The Language and its Implementation. John Wiley 1981, ISBN 0-471-27835-1
  • Peter Grogono: Programming in Pascal, Revised Edition, Addison-Wesley, 1980
  • Richard S. Forsyth: Pascal in Work and Play, Chapman and Hall, 1982
  • N. Wirth, M. Broy, ed, and E. Denert, ed: Pascal and its Successors in Software Pioneers: Contributions to Software Engineering. Springer-Verlag, 2002, ISBN 3-540-43081-4
  • N. Wirth: Recollections about the Development of Pascal. ACM SIGPLAN Notices, Volume 28, No 3, March 1993.


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C

C (/s/, as in the letter c) is a general-purpose, procedural computer programming language supporting structured programming, lexical variable scope, and recursion, while a static type system prevents unintended operations. By design, C provides constructs that map efficiently to typical machine instructions and has found lasting use in applications previously coded in assembly language. Such applications include operating systems and various application software for computers, from supercomputers to embedded systems.

C was originally developed at Bell Labs by Dennis Ritchie between 1972 and 1973 to make utilities running on Unix. Later, it was applied to re-implementing the kernel of the Unix operating system.[6] During the 1980s, C gradually gained popularity. It has become one of the most widely used programming languages,[7][8] with C compilers from various vendors available for the majority of existing computer architectures and operating systems. C has been standardized by the ANSI since 1989 (see ANSI C) and by the International Organization for Standardization.

C is an imperative procedural language. It was designed to be compiled using a relatively straightforward compiler to provide low-level access to memory and language constructs that map efficiently to machine instructions, all with minimal runtime support. Despite its low-level capabilities, the language was designed to encourage cross-platform programming. A standards-compliant C program written with portability in mind can be compiled for a wide variety of computer platforms and operating systems with few changes to its source code. The language is available on various platforms, from embedded microcontrollers to supercomputers.

Overview

Dennis Ritchie (right), the inventor of the C programming language, with Ken Thompson

Like most procedural languages in the ALGOL tradition, C has facilities for structured programming and allows lexical variable scope and recursion. Its static type system prevents unintended operations. In C, all executable code is contained within subroutines (also called “functions”, though not strictly in the sense of functional programming). Function parameters are always passed by value. Pass-by-reference is simulated in C by explicitly passing pointer values. C program source text is free-format, using the semicolon as a statement terminator and curly braces for grouping blocks of statements.

The C language also exhibits the following characteristics:

  • The language has a small, fixed number of keywords, including a full set of control flow primitives: if/else, for, do/while, while, and switch. User-defined names are not distinguished from keywords by any kind of sigil.
  • It has a large number of arithmetic, bitwise, and logic operators: +, +=, ++, &, ||, etc.
  • More than one assignment may be performed in a single statement.
  • Functions:
    • Function return values can be ignored, when not needed.
    • Function and data pointers permit ad hoc run-time polymorphism.
    • Functions may not be defined within the lexical scope of other functions.
  • Data typing is static, but weakly enforced; all data has a type, but implicit conversions are possible.
  • Declaration syntax mimics usage context. C has no “define” keyword; instead, a statement beginning with the name of a type is taken as a declaration. There is no “function” keyword; instead, a function is indicated by the presence of a parenthesized argument list.
  • User-defined (typedef) and compound types are possible.
    • Heterogeneous aggregate data types (struct) allow related data elements to be accessed and assigned as a unit.
    • Union is a structure with overlapping members; only the last member stored is valid.
    • Array indexing is a secondary notation, defined in terms of pointer arithmetic. Unlike structs, arrays are not first-class objects: they cannot be assigned or compared using single built-in operators. There is no “array” keyword in use or definition; instead, square brackets indicate arrays syntactically, for example month[11].
    • Enumerated types are possible with the enum keyword. They are freely interconvertible with integers.
    • Strings are not a distinct data type, but are conventionally implemented as null-terminated character arrays.
  • Low-level access to computer memory is possible by converting machine addresses to typed pointers.
  • Procedures (subroutines not returning values) are a special case of function, with an untyped return type void.
  • A preprocessor performs macro definition, source code file inclusion, and conditional compilation.
  • There is a basic form of modularity: files can be compiled separately and linked together, with control over which functions and data objects are visible to other files via static and extern attributes.
  • Complex functionality such as I/O, string manipulation, and mathematical functions are consistently delegated to library routines.

While C does not include certain features found in other languages (such as object orientation and garbage collection), these can be implemented or emulated, often through the use of external libraries (e.g., the GLib Object System or the Boehm garbage collector).

Relations to other languages

Many later languages have borrowed directly or indirectly from C, including C++, C#, Unix’s C shell, D, Go, Java, JavaScript (including transpilers), Limbo, LPC, Objective-C, Perl, PHP, Python, Rust, Swift, Verilog and SystemVerilog (hardware description languages).[5] These languages have drawn many of their control structures and other basic features from C. Most of them (Python being a dramatic exception) also express highly similar syntax to C, and they tend to combine the recognizable expression and statement syntax of C with underlying type systems, data models, and semantics that can be radically different.

History

Early developments

Timeline of language development
Year C Standard[9]
1972 Birth
1978 K&R C
1989/1990 ANSI C and ISO C
1999 C99
2011 C11
2017/2018 C18

The origin of C is closely tied to the development of the Unix operating system, originally implemented in assembly language on a PDP-7 by Dennis Ritchie and Ken Thompson, incorporating several ideas from colleagues. Eventually, they decided to port the operating system to a PDP-11. The original PDP-11 version of Unix was also developed in assembly language.[10]

Thompson desired a programming language to make utilities for the new platform. At first, he tried to make a Fortran compiler, but soon gave up the idea. Instead, he created a cut-down version of the recently developed BCPL systems programming language. The official description of BCPL was not available at the time,[11] and Thompson modified the syntax to be less wordy, producing the similar but somewhat simpler B.[10] However, few utilities were ultimately written in B because it was too slow, and B could not take advantage of PDP-11 features such as byte addressability.

In 1972, Ritchie started to improve B, which resulted in creating a new language C.[12] The C compiler and some utilities made with it were included in Version 2 Unix.[13]

At Version 4 Unix released in November 1973, the Unix kernel was extensively re-implemented by C.[10] By this time, the C language had acquired some powerful features such as struct types.

Unix was one of the first operating system kernels implemented in a language other than assembly. Earlier instances include the Multics system (which was written in PL/I) and Master Control Program (MCP) for the Burroughs B5000 (which was written in ALGOL) in 1961. In around 1977, Ritchie and Stephen C. Johnson made further changes to the language to facilitate portability of the Unix operating system. Johnson’s Portable C Compiler served as the basis for several implementations of C on new platforms.[12]

K&R C

The cover of the book The C Programming Language, first edition, by Brian Kernighan and Dennis Ritchie

In 1978, Brian Kernighan and Dennis Ritchie published the first edition of The C Programming Language.[1] This book, known to C programmers as K&R, served for many years as an informal specification of the language. The version of C that it describes is commonly referred to as “K&R C”. The second edition of the book[14] covers the later ANSI C standard, described below.

K&R introduced several language features:

  • Standard I/O library
  • long int data type
  • unsigned int data type
  • Compound assignment operators of the form =op (such as =-) were changed to the form op= (that is, -=) to remove the semantic ambiguity created by constructs such as i=-10, which had been interpreted as i =- 10 (decrement i by 10) instead of the possibly intended i = -10 (let i be -10).

Even after the publication of the 1989 ANSI standard, for many years K&R C was still considered the “lowest common denominator” to which C programmers restricted themselves when maximum portability was desired, since many older compilers were still in use, and because carefully written K&R C code can be legal Standard C as well.

In early versions of C, only functions that return types other than int must be declared if used before the function definition; functions used without prior declaration were presumed to return type int.

For example:

long some_function();
/* int */ other_function();

/* int */ calling_function()
{
    long test1;
    register /* int */ test2;

    test1 = some_function();
    if (test1 > 0)
          test2 = 0;
    else
          test2 = other_function();
    return test2;
}

The int type specifiers which are commented out could be omitted in K&R C, but are required in later standards.

Since K&R function declarations did not include any information about function arguments, function parameter type checks were not performed, although some compilers would issue a warning message if a local function was called with the wrong number of arguments, or if multiple calls to an external function used different numbers or types of arguments. Separate tools such as Unix’s lint utility were developed that (among other things) could check for consistency of function use across multiple source files.

In the years following the publication of K&R C, several features were added to the language, supported by compilers from AT&T (in particular PCC[15]) and some other vendors. These included:

The large number of extensions and lack of agreement on a standard library, together with the language popularity and the fact that not even the Unix compilers precisely implemented the K&R specification, led to the necessity of standardization.

ANSI C and ISO C

During the late 1970s and 1980s, versions of C were implemented for a wide variety of mainframe computers, minicomputers, and microcomputers, including the IBM PC, as its popularity began to increase significantly.

In 1983, the American National Standards Institute (ANSI) formed a committee, X3J11, to establish a standard specification of C. X3J11 based the C standard on the Unix implementation; however, the non-portable portion of the Unix C library was handed off to the IEEE working group 1003 to become the basis for the 1988 POSIX standard. In 1989, the C standard was ratified as ANSI X3.159-1989 “Programming Language C”. This version of the language is often referred to as ANSI C, Standard C, or sometimes C89.

In 1990, the ANSI C standard (with formatting changes) was adopted by the International Organization for Standardization (ISO) as ISO/IEC 9899:1990, which is sometimes called C90. Therefore, the terms “C89” and “C90” refer to the same programming language.

ANSI, like other national standards bodies, no longer develops the C standard independently, but defers to the international C standard, maintained by the working group ISO/IEC JTC1/SC22/WG14. National adoption of an update to the international standard typically occurs within a year of ISO publication.

One of the aims of the C standardization process was to produce a superset of K&R C, incorporating many of the subsequently introduced unofficial features. The standards committee also included several additional features such as function prototypes (borrowed from C++), void pointers, support for international character sets and locales, and preprocessor enhancements. Although the syntax for parameter declarations was augmented to include the style used in C++, the K&R interface continued to be permitted, for compatibility with existing source code.

C89 is supported by current C compilers, and most modern C code is based on it. Any program written only in Standard C and without any hardware-dependent assumptions will run correctly on any platform with a conforming C implementation, within its resource limits. Without such precautions, programs may compile only on a certain platform or with a particular compiler, due, for example, to the use of non-standard libraries, such as GUI libraries, or to a reliance on compiler- or platform-specific attributes such as the exact size of data types and byte endianness.

In cases where code must be compilable by either standard-conforming or K&R C-based compilers, the __STDC__ macro can be used to split the code into Standard and K&R sections to prevent the use on a K&R C-based compiler of features available only in Standard C.

After the ANSI/ISO standardization process, the C language specification remained relatively static for several years. In 1995, Normative Amendment 1 to the 1990 C standard (ISO/IEC 9899/AMD1:1995, known informally as C95) was published, to correct some details and to add more extensive support for international character sets.[16]

C99

The C standard was further revised in the late 1990s, leading to the publication of ISO/IEC 9899:1999 in 1999, which is commonly referred to as “C99“. It has since been amended three times by Technical Corrigenda.[17]

C99 introduced several new features, including inline functions, several new data types (including long long int and a complex type to represent complex numbers), variable-length arrays and flexible array members, improved support for IEEE 754 floating point, support for variadic macros (macros of variable arity), and support for one-line comments beginning with //, as in BCPL or C++. Many of these had already been implemented as extensions in several C compilers.

C99 is for the most part backward compatible with C90, but is stricter in some ways; in particular, a declaration that lacks a type specifier no longer has int implicitly assumed. A standard macro __STDC_VERSION__ is defined with value 199901L to indicate that C99 support is available. GCC, Solaris Studio, and other C compilers now support many or all of the new features of C99. The C compiler in Microsoft Visual C++, however, implements the C89 standard and those parts of C99 that are required for compatibility with C++11.[18]

C11

In 2007, work began on another revision of the C standard, informally called “C1X” until its official publication on 2011-12-08. The C standards committee adopted guidelines to limit the adoption of new features that had not been tested by existing implementations.

The C11 standard adds numerous new features to C and the library, including type generic macros, anonymous structures, improved Unicode support, atomic operations, multi-threading, and bounds-checked functions. It also makes some portions of the existing C99 library optional, and improves compatibility with C++. The standard macro __STDC_VERSION__ is defined as 201112L to indicate that C11 support is available.

C18

Published in June 2018, C18 is the current standard for the C programming language. It introduces no new language features, only technical corrections and clarifications to defects in C11. The standard macro __STDC_VERSION__ is defined as 201710L.

Embedded C

Historically, embedded C programming requires nonstandard extensions to the C language in order to support exotic features such as fixed-point arithmetic, multiple distinct memory banks, and basic I/O operations.

In 2008, the C Standards Committee published a technical report extending the C language[19] to address these issues by providing a common standard for all implementations to adhere to. It includes a number of features not available in normal C, such as fixed-point arithmetic, named address spaces, and basic I/O hardware addressing.

Syntax

C has a formal grammar specified by the C standard.[20] Line endings are generally not significant in C; however, line boundaries do have significance during the preprocessing phase. Comments may appear either between the delimiters /* and */, or (since C99) following // until the end of the line. Comments delimited by /* and */ do not nest, and these sequences of characters are not interpreted as comment delimiters if they appear inside string or character literals.[21]

C source files contain declarations and function definitions. Function definitions, in turn, contain declarations and statements. Declarations either define new types using keywords such as struct, union, and enum, or assign types to and perhaps reserve storage for new variables, usually by writing the type followed by the variable name. Keywords such as char and int specify built-in types. Sections of code are enclosed in braces ({ and }, sometimes called “curly brackets”) to limit the scope of declarations and to act as a single statement for control structures.

As an imperative language, C uses statements to specify actions. The most common statement is an expression statement, consisting of an expression to be evaluated, followed by a semicolon; as a side effect of the evaluation, functions may be called and variables may be assigned new values. To modify the normal sequential execution of statements, C provides several control-flow statements identified by reserved keywords. Structured programming is supported by if(-else) conditional execution and by dowhile, while, and for iterative execution (looping). The for statement has separate initialization, testing, and reinitialization expressions, any or all of which can be omitted. break and continue can be used to leave the innermost enclosing loop statement or skip to its reinitialization. There is also a non-structured goto statement which branches directly to the designated label within the function. switch selects a case to be executed based on the value of an integer expression.

Expressions can use a variety of built-in operators and may contain function calls. The order in which arguments to functions and operands to most operators are evaluated is unspecified. The evaluations may even be interleaved. However, all side effects (including storage to variables) will occur before the next “sequence point“; sequence points include the end of each expression statement, and the entry to and return from each function call. Sequence points also occur during evaluation of expressions containing certain operators (&&, ||, ?: and the comma operator). This permits a high degree of object code optimization by the compiler, but requires C programmers to take more care to obtain reliable results than is needed for other programming languages.

Kernighan and Ritchie say in the Introduction of The C Programming Language: “C, like any other language, has its blemishes. Some of the operators have the wrong precedence; some parts of the syntax could be better.”[22] The C standard did not attempt to correct many of these blemishes, because of the impact of such changes on already existing software.

Character set

The basic C source character set includes the following characters:

Newline indicates the end of a text line; it need not correspond to an actual single character, although for convenience C treats it as one.

Additional multi-byte encoded characters may be used in string literals, but they are not entirely portable. The latest C standard (C11) allows multi-national Unicode characters to be embedded portably within C source text by using uXXXX or UXXXXXXXX encoding (where the X denotes a hexadecimal character), although this feature is not yet widely implemented.

The basic C execution character set contains the same characters, along with representations for alert, backspace, and carriage return. Run-time support for extended character sets has increased with each revision of the C standard.

Reserved words

C89 has 32 reserved words, also known as keywords, which are the words that cannot be used for any purposes other than those for which they are predefined:

C99 reserved five more words:

C11 reserved seven more words:[23]

Most of the recently reserved words begin with an underscore followed by a capital letter, because identifiers of that form were previously reserved by the C standard for use only by implementations. Since existing program source code should not have been using these identifiers, it would not be affected when C implementations started supporting these extensions to the programming language. Some standard headers do define more convenient synonyms for underscored identifiers. The language previously included a reserved word called entry, but this was seldom implemented, and has now been removed as a reserved word.[24]

Operators

C supports a rich set of operators, which are symbols used within an expression to specify the manipulations to be performed while evaluating that expression. C has operators for:

C uses the operator = (used in mathematics to express equality) to indicate assignment, following the precedent of Fortran and PL/I, but unlike ALGOL and its derivatives. C uses the operator == to test for equality. The similarity between these two operators (assignment and equality) may result in the accidental use of one in place of the other, and in many cases, the mistake does not produce an error message (although some compilers produce warnings). For example, the conditional expression if (a == b + 1) might mistakenly be written as if (a = b + 1), which will be evaluated as true if a is not zero after the assignment.[25]

The C operator precedence is not always intuitive. For example, the operator == binds more tightly than (is executed prior to) the operators & (bitwise AND) and | (bitwise OR) in expressions such as x & 1 == 0, which must be written as (x & 1) == 0 if that is the coder's intent.[26]

"Hello, world" example

The "hello, world" example, which appeared in the first edition of K&R, has become the model for an introductory program in most programming textbooks. The program prints "hello, world" to the standard output, which is usually a terminal or screen display.

The original version was:[27]

main()
{
    printf("hello, worldn");
}

A standard-conforming "hello, world" program is:[a]

#include 

int main(void)
{
    printf("hello, worldn");
}

The first line of the program contains a preprocessing directive, indicated by #include. This causes the compiler to replace that line with the entire text of the stdio.h standard header, which contains declarations for standard input and output functions such as printf and scanf. The angle brackets surrounding stdio.h indicate that stdio.h is located using a search strategy that prefers headers provided with the compiler to other headers having the same name, as opposed to double quotes which typically include local or project-specific header files.

The next line indicates that a function named main is being defined. The main function serves a special purpose in C programs; the run-time environment calls the main function to begin program execution. The type specifier int indicates that the value that is returned to the invoker (in this case the run-time environment) as a result of evaluating the main function, is an integer. The keyword void as a parameter list indicates that this function takes no arguments.[b]

The opening curly brace indicates the beginning of the definition of the main function.

The next line calls (diverts execution to) a function named printf, which in this case is supplied from a system library. In this call, the printf function is passed (provided with) a single argument, the address of the first character in the string literal "hello, worldn". The string literal is an unnamed array with elements of type char, set up automatically by the compiler with a final 0-valued character to mark the end of the array (printf needs to know this). The n is an escape sequence that C translates to a newline character, which on output signifies the end of the current line. The return value of the printf function is of type int, but it is silently discarded since it is not used. (A more careful program might test the return value to determine whether or not the printf function succeeded.) The semicolon ; terminates the statement.

The closing curly brace indicates the end of the code for the main function. According to the C99 specification and newer, the main function, unlike any other function, will implicitly return a value of 0 upon reaching the } that terminates the function. (Formerly an explicit return 0; statement was required.) This is interpreted by the run-time system as an exit code indicating successful execution.[28]

Data types

The type system in C is static and weakly typed, which makes it similar to the type system of ALGOL descendants such as Pascal.[29] There are built-in types for integers of various sizes, both signed and unsigned, floating-point numbers, and enumerated types (enum). Integer type char is often used for single-byte characters. C99 added a boolean datatype. There are also derived types including arrays, pointers, records (struct), and unions (union).

C is often used in low-level systems programming where escapes from the type system may be necessary. The compiler attempts to ensure type correctness of most expressions, but the programmer can override the checks in various ways, either by using a type cast to explicitly convert a value from one type to another, or by using pointers or unions to reinterpret the underlying bits of a data object in some other way.

Some find C's declaration syntax unintuitive, particularly for function pointers. (Ritchie's idea was to declare identifiers in contexts resembling their use: "declaration reflects use".)[30]

C's usual arithmetic conversions allow for efficient code to be generated, but can sometimes produce unexpected results. For example, a comparison of signed and unsigned integers of equal width requires a conversion of the signed value to unsigned. This can generate unexpected results if the signed value is negative.

Pointers

C supports the use of pointers, a type of reference that records the address or location of an object or function in memory. Pointers can be dereferenced to access data stored at the address pointed to, or to invoke a pointed-to function. Pointers can be manipulated using assignment or pointer arithmetic. The run-time representation of a pointer value is typically a raw memory address (perhaps augmented by an offset-within-word field), but since a pointer's type includes the type of the thing pointed to, expressions including pointers can be type-checked at compile time. Pointer arithmetic is automatically scaled by the size of the pointed-to data type. Pointers are used for many purposes in C. Text strings are commonly manipulated using pointers into arrays of characters. Dynamic memory allocation is performed using pointers. Many data types, such as trees, are commonly implemented as dynamically allocated struct objects linked together using pointers. Pointers to functions are useful for passing functions as arguments to higher-order functions (such as qsort or bsearch) or as callbacks to be invoked by event handlers.[28]

A null pointer value explicitly points to no valid location. Dereferencing a null pointer value is undefined, often resulting in a segmentation fault. Null pointer values are useful for indicating special cases such as no "next" pointer in the final node of a linked list, or as an error indication from functions returning pointers. In appropriate contexts in source code, such as for assigning to a pointer variable, a null pointer constant can be written as 0, with or without explicit casting to a pointer type, or as the NULL macro defined by several standard headers. In conditional contexts, null pointer values evaluate to false, while all other pointer values evaluate to true.

Void pointers (void *) point to objects of unspecified type, and can therefore be used as "generic" data pointers. Since the size and type of the pointed-to object is not known, void pointers cannot be dereferenced, nor is pointer arithmetic on them allowed, although they can easily be (and in many contexts implicitly are) converted to and from any other object pointer type.[28]

Careless use of pointers is potentially dangerous. Because they are typically unchecked, a pointer variable can be made to point to any arbitrary location, which can cause undesirable effects. Although properly used pointers point to safe places, they can be made to point to unsafe places by using invalid pointer arithmetic; the objects they point to may continue to be used after deallocation (dangling pointers); they may be used without having been initialized (wild pointers); or they may be directly assigned an unsafe value using a cast, union, or through another corrupt pointer. In general, C is permissive in allowing manipulation of and conversion between pointer types, although compilers typically provide options for various levels of checking. Some other programming languages address these problems by using more restrictive reference types.

Arrays

Array types in C are traditionally of a fixed, static size specified at compile time. (The more recent C99 standard also allows a form of variable-length arrays.) However, it is also possible to allocate a block of memory (of arbitrary size) at run-time, using the standard library's malloc function, and treat it as an array. C's unification of arrays and pointers means that declared arrays and these dynamically allocated simulated arrays are virtually interchangeable.

Since arrays are always accessed (in effect) via pointers, array accesses are typically not checked against the underlying array size, although some compilers may provide bounds checking as an option.[31][32] Array bounds violations are therefore possible and rather common in carelessly written code, and can lead to various repercussions, including illegal memory accesses, corruption of data, buffer overruns, and run-time exceptions. If bounds checking is desired, it must be done manually.

C does not have a special provision for declaring multi-dimensional arrays, but rather relies on recursion within the type system to declare arrays of arrays, which effectively accomplishes the same thing. The index values of the resulting "multi-dimensional array" can be thought of as increasing in row-major order.

Multi-dimensional arrays are commonly used in numerical algorithms (mainly from applied linear algebra) to store matrices. The structure of the C array is well suited to this particular task. However, since arrays are passed merely as pointers, the bounds of the array must be known fixed values or else explicitly passed to any subroutine that requires them, and dynamically sized arrays of arrays cannot be accessed using double indexing. (A workaround for this is to allocate the array with an additional "row vector" of pointers to the columns.)

C99 introduced "variable-length arrays" which address some, but not all, of the issues with ordinary C arrays.

Array–pointer interchangeability

The subscript notation x[i] (where x designates a pointer) is syntactic sugar for *(x+i).[33] Taking advantage of the compiler's knowledge of the pointer type, the address that x + i points to is not the base address (pointed to by x) incremented by i bytes, but rather is defined to be the base address incremented by i multiplied by the size of an element that x points to. Thus, x[i] designates the i+1th element of the array.

Furthermore, in most expression contexts (a notable exception is as operand of sizeof), the name of an array is automatically converted to a pointer to the array's first element. This implies that an array is never copied as a whole when named as an argument to a function, but rather only the address of its first element is passed. Therefore, although function calls in C use pass-by-value semantics, arrays are in effect passed by reference.

The size of an element can be determined by applying the operator sizeof to any dereferenced element of x, as in n = sizeof *x or n = sizeof x[0], and the number of elements in a declared array A can be determined as sizeof A / sizeof A[0]. The latter only applies to array names: variables declared with subscripts (int A[20]). Due to the semantics of C, it is not possible to determine the entire size of arrays through pointers to arrays or those created by dynamic allocation (malloc); code such as sizeof arr / sizeof arr[0] (where arr designates a pointer) will not work since the compiler assumes the size of the pointer itself is being requested.[34][35] Since array name arguments to sizeof are not converted to pointers, they do not exhibit such ambiguity. However, arrays created by dynamic allocation are accessed by pointers rather than true array variables, so they suffer from the same sizeof issues as array pointers.

Thus, despite this apparent equivalence between array and pointer variables, there is still a distinction to be made between them. Even though the name of an array is, in most expression contexts, converted into a pointer (to its first element), this pointer does not itself occupy any storage; the array name is not an l-value, and its address is a constant, unlike a pointer variable. Consequently, what an array "points to" cannot be changed, and it is impossible to assign a new address to an array name. Array contents may be copied, however, by using the memcpy function, or by accessing the individual elements.

Memory management

One of the most important functions of a programming language is to provide facilities for managing memory and the objects that are stored in memory. C provides three distinct ways to allocate memory for objects:[28]

  • Static memory allocation: space for the object is provided in the binary at compile-time; these objects have an extent (or lifetime) as long as the binary which contains them is loaded into memory.
  • Automatic memory allocation: temporary objects can be stored on the stack, and this space is automatically freed and reusable after the block in which they are declared is exited.
  • Dynamic memory allocation: blocks of memory of arbitrary size can be requested at run-time using library functions such as malloc from a region of memory called the heap; these blocks persist until subsequently freed for reuse by calling the library function realloc or free

These three approaches are appropriate in different situations and have various trade-offs. For example, static memory allocation has little allocation overhead, automatic allocation may involve slightly more overhead, and dynamic memory allocation can potentially have a great deal of overhead for both allocation and deallocation. The persistent nature of static objects is useful for maintaining state information across function calls, automatic allocation is easy to use but stack space is typically much more limited and transient than either static memory or heap space, and dynamic memory allocation allows convenient allocation of objects whose size is known only at run-time. Most C programs make extensive use of all three.

Where possible, automatic or static allocation is usually simplest because the storage is managed by the compiler, freeing the programmer of the potentially error-prone chore of manually allocating and releasing storage. However, many data structures can change in size at runtime, and since static allocations (and automatic allocations before C99) must have a fixed size at compile-time, there are many situations in which dynamic allocation is necessary.[28] Prior to the C99 standard, variable-sized arrays were a common example of this. (See the article on malloc for an example of dynamically allocated arrays.) Unlike automatic allocation, which can fail at run time with uncontrolled consequences, the dynamic allocation functions return an indication (in the form of a null pointer value) when the required storage cannot be allocated. (Static allocation that is too large is usually detected by the linker or loader, before the program can even begin execution.)

Unless otherwise specified, static objects contain zero or null pointer values upon program startup. Automatically and dynamically allocated objects are initialized only if an initial value is explicitly specified; otherwise they initially have indeterminate values (typically, whatever bit pattern happens to be present in the storage, which might not even represent a valid value for that type). If the program attempts to access an uninitialized value, the results are undefined. Many modern compilers try to detect and warn about this problem, but both false positives and false negatives can occur.

Another issue is that heap memory allocation has to be synchronized with its actual usage in any program in order for it to be reused as much as possible. For example, if the only pointer to a heap memory allocation goes out of scope or has its value overwritten before free() is called, then that memory cannot be recovered for later reuse and is essentially lost to the program, a phenomenon known as a memory leak. Conversely, it is possible for memory to be freed but continue to be referenced, leading to unpredictable results. Typically, the symptoms will appear in a portion of the program far removed from the actual error, making it difficult to track down the problem. (Such issues are ameliorated in languages with automatic garbage collection.)

Libraries

The C programming language uses libraries as its primary method of extension. In C, a library is a set of functions contained within a single "archive" file. Each library typically has a header file, which contains the prototypes of the functions contained within the library that may be used by a program, and declarations of special data types and macro symbols used with these functions. In order for a program to use a library, it must include the library's header file, and the library must be linked with the program, which in many cases requires compiler flags (e.g., -lm, shorthand for "link the math library").[28]

The most common C library is the C standard library, which is specified by the ISO and ANSI C standards and comes with every C implementation (implementations which target limited environments such as embedded systems may provide only a subset of the standard library). This library supports stream input and output, memory allocation, mathematics, character strings, and time values. Several separate standard headers (for example, stdio.h) specify the interfaces for these and other standard library facilities.

Another common set of C library functions are those used by applications specifically targeted for Unix and Unix-like systems, especially functions which provide an interface to the kernel. These functions are detailed in various standards such as POSIX and the Single UNIX Specification.

Since many programs have been written in C, there are a wide variety of other libraries available. Libraries are often written in C because C compilers generate efficient object code; programmers then create interfaces to the library so that the routines can be used from higher-level languages like Java, Perl, and Python.[28]

File handling and streams

File input and output (I/O) is not part of the C language itself but instead is handled by libraries (such as the C standard library) and their associated header files (e.g. stdio.h). File handling is generally implemented through high-level I/O which works through streams. A stream is from this perspective a data flow that is independent of devices, while a file is a concrete device. The high level I/O is done through the association of a stream to a file. In the C standard library, a buffer (a memory area or queue) is temporarily used to store data before it's sent to the final destination. This reduces the time spent waiting for slower devices, for example a hard drive or solid state drive. Low-level I/O functions are not part of the standard C library but are generally part of "bare metal" programming (programming that's independent of any operating system such as most but not all embedded programming). With few exceptions, implementations include low-level I/O.

Language tools

A number of tools have been developed to help C programmers find and fix statements with undefined behavior or possibly erroneous expressions, with greater rigor than that provided by the compiler. The tool lint was the first such, leading to many others.

Automated source code checking and auditing are beneficial in any language, and for C many such tools exist, such as Lint. A common practice is to use Lint to detect questionable code when a program is first written. Once a program passes Lint, it is then compiled using the C compiler. Also, many compilers can optionally warn about syntactically valid constructs that are likely to actually be errors. MISRA C is a proprietary set of guidelines to avoid such questionable code, developed for embedded systems.[36]

There are also compilers, libraries, and operating system level mechanisms for performing actions that are not a standard part of C, such as bounds checking for arrays, detection of buffer overflow, serialization, dynamic memory tracking, and automatic garbage collection.

Tools such as Purify or Valgrind and linking with libraries containing special versions of the memory allocation functions can help uncover runtime errors in memory usage.

Uses

The TIOBE index graph, showing a comparison of the popularity of various programming languages[37]

C is widely used for systems programming in implementing operating systems and embedded system applications,[38] because C code, when written for portability, can be used for most purposes, yet when needed, system-specific code can be used to access specific hardware addresses and to perform type punning to match externally imposed interface requirements, with a low run-time demand on system resources.

C can also be used for website programming using CGI as a "gateway" for information between the Web application, the server, and the browser.[39] C is often chosen over interpreted languages because of its speed, stability, and near-universal availability.[40]

One consequence of C's wide availability and efficiency is that compilers, libraries and interpreters of other programming languages are often implemented in C. The reference implementations of Python, Perl and PHP, for example, are all written in C.

Because the layer of abstraction is thin and the overhead is low, C enables programmers to create efficient implementations of algorithms and data structures, useful for computationally intense programs. For example, the GNU Multiple Precision Arithmetic Library, the GNU Scientific Library, Mathematica, and MATLAB are completely or partially written in C.

C is sometimes used as an intermediate language by implementations of other languages. This approach may be used for portability or convenience; by using C as an intermediate language, additional machine-specific code generators are not necessary. C has some features, such as line-number preprocessor directives and optional superfluous commas at the end of initializer lists, that support compilation of generated code. However, some of C's shortcomings have prompted the development of other C-based languages specifically designed for use as intermediate languages, such as C--.

C has also been widely used to implement end-user applications. However, such applications can also be written in newer, higher-level languages.

Related languages

C has both directly and indirectly influenced many later languages such as C#, D, Go, Java, JavaScript, Limbo, LPC, Perl, PHP, Python, and Unix's C shell.[41] The most pervasive influence has been syntactical, all of the languages mentioned combine the statement and (more or less recognizably) expression syntax of C with type systems, data models and/or large-scale program structures that differ from those of C, sometimes radically.

Several C or near-C interpreters exist, including Ch and CINT, which can also be used for scripting.

When object-oriented languages became popular, C++ and Objective-C were two different extensions of C that provided object-oriented capabilities. Both languages were originally implemented as source-to-source compilers; source code was translated into C, and then compiled with a C compiler.[42]

The C++ programming language was devised by Bjarne Stroustrup as an approach to providing object-oriented functionality with a C-like syntax.[43] C++ adds greater typing strength, scoping, and other tools useful in object-oriented programming, and permits generic programming via templates. Nearly a superset of C, C++ now supports most of C, with a few exceptions.

Objective-C was originally a very "thin" layer on top of C, and remains a strict superset of C that permits object-oriented programming using a hybrid dynamic/static typing paradigm. Objective-C derives its syntax from both C and Smalltalk: syntax that involves preprocessing, expressions, function declarations, and function calls is inherited from C, while the syntax for object-oriented features was originally taken from Smalltalk.

In addition to C++ and Objective-C, Ch, Cilk and Unified Parallel C are nearly supersets of C.

Notes

Sources

Further reading


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Programming language

The source code for a simple computer program written in the C programming language. When compiled and run, it will give the output “Hello, world!“.

A programming language is a formal language, which comprises a set of instructions that produce various kinds of output. Programming languages are used in computer programming to implement algorithms.

Most programming languages consist of instructions for computers. There are programmable machines that use a set of specific instructions, rather than general programming languages. Early ones preceded the invention of the digital computer, the first probably being the automatic flute player described in the 9th century by the brothers Musa in Baghdad, during the Islamic Golden Age.[1] Since the early 1800s, programs have been used to direct the behavior of machines such as Jacquard looms, music boxes and player pianos.[2] 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 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 (form) and semantics (meaning). 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. Some languages have both, with the basic language defined by a standard and extensions taken from the dominant implementation being common.

Definitions[edit]

A programming language is a notation for writing programs, which are specifications of a computation or algorithm.[3] Some authors restrict the term “programming language” to those languages that can express all possible algorithms.[3][4] Traits often considered important for what constitutes a programming language include:

Function and target
A computer programming language is a language used to write computer programs, which involves a computer performing some kind of computation[5] or algorithm and possibly control external devices such as printers, disk drives, robots,[6] 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.[7] In most practical contexts, a programming language involves a computer; consequently, programming languages are usually defined and studied this way.[8] 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.
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.[9] This principle is sometimes formulated as a recommendation to the programmer to make proper use of such abstractions.[10]
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 often called programming languages.[11][12]

Markup languages like XML, HTML, or troff, which define structured data, are not usually considered programming languages.[13][14][15] Programming languages may, however, share the syntax with markup languages if a computational semantics is defined. XSLT, for example, is a Turing complete language entirely using XML syntax.[16][17][18] Moreover, LaTeX, which is mostly used for structuring documents, also contains a Turing complete subset.[19][20]

The term computer language is sometimes used interchangeably with programming language.[21] 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.[22] 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.[23]

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.[24]John C. Reynolds emphasizes that formal specification 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.[25]

History[edit]

Early developments[edit]

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.

Slightly later, programs could be written in machine language, 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 location 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 cards, paper tape, magnetic tape or toggled in on switches on the front panel of the computer. Machine languages were later termed first-generation programming languages (1GL).

The next step was development of so-called second-generation programming languages (2GL) or assembly languages, which were still closely tied to the instruction set architecture of the specific computer. These served to make the program much more human-readable and relieved the programmer of tedious and error-prone address calculations.

The first high-level programming languages, or third-generation programming languages (3GL), were written in the 1950s. 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. However, it was not implemented until 1998 and 2000.[26]

John Mauchly‘s Short Code, proposed in 1949, was one of the first high-level languages ever developed for an electronic computer.[27] Unlike machine code, 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, Alick Glennie developed Autocode in the early 1950s. As a programming language, it used a compiler to automatically convert the language into machine code. 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.[28][29]

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 Mercury in the 1950s in conjunction with the University of Manchester. The version for the EDSAC 2 was devised by D. F. Hartley of University of Cambridge Mathematical Laboratory 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 was developed for the University of Manchester Atlas 1 machine.

In 1954, FORTRAN was invented at IBM by 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.[30][31] It is still a popular language for high-performance computing[32] and is used for programs that benchmark and rank the world’s fastest supercomputers.[33]

Another early programming language was devised by Grace Hopper in the US, called FLOW-MATIC. It was developed for the UNIVAC I at Remington Rand 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 programming language and implemented a prototype.[34] The FLOW-MATIC compiler became publicly available in early 1958 and was substantially complete in 1959.[35] 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.[36]

Refinement[edit]

The increased use of high-level languages introduced a requirement for low-level programming languages or system programming languages. These languages, to varying degrees, provide facilities between assembly languages and high-level languages. They can be used to perform tasks which 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:

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

The 1960s and 1970s also saw considerable debate over the merits of structured programming, and whether programming languages should be designed to support it.[39]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.[40]

Consolidation and growth[edit]

A selection of textbooks that teach programming, in languages both popular and obscure. These are only a few of the thousands of programming languages and dialects that have been designed in history.

The 1980s were years of relative consolidation. C++ combined object-oriented and systems programming. The United States government standardized Ada, a systems programming language derived from Pascal and intended for use by defense contractors. In Japan and elsewhere, vast sums were spent investigating so-called “fifth-generation” languages that incorporated logic programming constructs.[41] The functional languages community moved to standardize ML and Lisp. Rather than inventing new paradigms, all of these movements elaborated upon the ideas invented in the previous decades.

One important trend in language design for programming large-scale systems during the 1980s was an increased focus on the use of modules or large-scale organizational units of code. Modula-2, Ada, and ML all developed notable module systems in the 1980s, which were often wedded to generic programming constructs.[42]

The rapid growth of the Internet in the mid-1990s created opportunities for new languages. Perl, originally a Unix scripting tool first released in 1987, became common in dynamic websites. 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). 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, delegates, aspects), and database integration such as Microsoft’s LINQ.

Fourth-generation programming languages (4GL) are computer programming languages which 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 written by a programmer.

Elements[edit]

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

Syntax[edit]

Parse tree of Python code with inset tokenization

Syntax highlighting is often used to aid programmers in recognizing elements of source code. The language above is Python.

A programming language’s surface form is known as its syntax. Most programming languages are purely textual; they use sequences of text including words, numbers, and punctuation, much like written natural languages. On the other hand, there are some programming languages which are more 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 or hard-coded in a 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 structure) and Backus–Naur form (for grammatical structure). Below is a simple grammar, based on Lisp:

expression ::= atom | list
atom       ::= number | symbol
number     ::= [+-]?['0'-'9']+
symbol     ::= ['A'-'Z''a'-'z'].*
list       ::= '(' expression* ')'

This grammar specifies the following:

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

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

Not all syntactically correct programs are semantically correct. Many syntactically correct programs are nonetheless ill-formed, per the language’s rules; and may (depending on the language specification and the soundness of the implementation) result in an error on translation or execution. In some cases, such programs may exhibit undefined behavior. Even when a program is well-defined within a language, it may still have a meaning that is not intended by the person who wrote it.

Using natural language as an example, it may not be possible to assign a meaning to a grammatically correct sentence or the sentence may be false:

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):

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.[43] 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.[44] 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.[45]

Semantics[edit]

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

Static semantics[edit]

The static semantics defines restrictions on the structure of valid texts that are hard or impossible to express in standard syntactic formalisms.[3] 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.[46] 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 analyses like data flow analysis may also be part of static semantics. Newer programming languages like Java and C# have definite assignment analysis, a form of data flow analysis, as part of their static semantics.

Dynamic semantics[edit]

Once data has been specified, the machine must be instructed to perform operations on the data. For example, the semantics may define the strategy by which expressions are evaluated to values, or the manner in which control structures conditionally execute 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[edit]

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

Typed versus untyped languages[edit]

A language is typed if the specification of every operation defines types of data to which the operation is applicable.[47] For example, the data represented by "this text between the quotes" is a string, and in many programming languages dividing a number by a string has no meaning and will not be executed. The invalid operation may be detected when the program is compiled (“static” type checking) and will be rejected by the compiler with a compilation error message, or it may be detected while the program is running (“dynamic” type checking), resulting in a run-time exception. Many languages allow a function called an exception handler to handle this exception and, for example, always return “-1” as the result.

A special case of typed languages are the single-typed languages. These are often scripting or markup languages, such as REXX or SGML, and have only one data type[dubious ]–—most commonly character strings which are used for both symbolic and numeric data.

In contrast, an untyped language, such as most assembly languages, allows any operation to be performed on any data, generally sequences of bits of various lengths.[47] High-level untyped languages include BCPL, Tcl, and some varieties of 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.[47] 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).

Static versus dynamic typing[edit]

In 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.[47]

Statically typed languages can be either manifestly typed or type-inferred. In the first case, the programmer must explicitly write types at certain textual positions (for example, at variable declarations). In the second case, the compiler infers the types of expressions and declarations based on context. Most mainstream statically typed languages, such as C++, C# and Java, are manifestly typed. Complete type inference has traditionally been associated with less mainstream languages, such as Haskell and ML. However, many manifestly typed languages support partial type inference; for example, C++, Java and C# all infer types in certain limited cases.[48] Additionally, some programming languages allow for some types to be automatically converted to other types; for example, an int can be used where the program expects a float.

Dynamic typing, 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.[47] As with type-inferred languages, dynamically typed languages do not require the programmer to write explicit type annotations on expressions. Among other things, this may permit a single variable to refer to values of different types at different points in the program execution. However, type errors cannot be automatically detected until a piece of code is actually executed, potentially making debugging more difficult. Lisp, Smalltalk, Perl, Python, JavaScript, and Ruby are all examples of dynamically typed languages.

Weak and strong typing[edit]

Weak typing allows a value of one type to be treated as another, for example treating a string as a number.[47] 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.

Strong typing prevents these program faults. An attempt to perform an operation on the wrong type of value raises an error.[47] Strongly typed languages are often termed type-safe or safe.

An alternative definition for “weakly typed” refers to languages, such as Perl 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.[49][50]

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[edit]

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. 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, a string literal is defined as an instance of the java.lang.String class; similarly, in Smalltalk, an anonymous function expression (a “block”) constructs an instance of the library’s BlockContext class. Conversely, Scheme 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[edit]

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.[51][52] 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.[53] 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.[54] The need for diverse programming languages arises from the diversity of contexts in which languages are used:

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

One common trend in the development of programming languages has been to add more ability to solve problems using a higher level of abstraction. The earliest programming languages were tied very closely to the underlying hardware of the computer. As new programming languages have developed, features have been added that let programmers express ideas that are more remote from simple translation into underlying hardware instructions. Because programmers are less tied to the complexity of the computer, their programs can do more computing with less effort from the programmer. This lets them write more functionality per time unit.[55]


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”.[56]Alan Perlis was similarly dismissive of the idea.[57] 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[edit]

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.

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

Implementation[edit]

An implementation of a programming language provides a way to write programs in that language and execute them on one or more configurations of hardware and software. There are, broadly, two approaches to programming language implementation: compilation and interpretation. It is generally possible to implement a language using either technique.

The output of a 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.[61][better source needed]

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[edit]

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,[62] and Microsoft‘s C# programming language, which has open implementations of most parts of the system, also has Common Language Runtime (CLR) as a closed environment.[63]

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 was originally an Ericsson’s internal programming language.[64]

Use[edit]

Thousands of different programming languages have been created, mainly in the computing field.[65]
Software is commonly built with 5 programming languages or more.[66]

Programming languages differ from most other forms of human expression in that they require a greater degree of precision and completeness. When using a natural language to communicate with other people, human authors and speakers can be ambiguous and make small errors, and still expect their intent to be understood. However, figuratively speaking, computers “do exactly what they are told to do”, and cannot “understand” what code the programmer intended to write. The combination of the language definition, a program, and the program’s inputs must fully specify the external behavior that occurs when the program is executed, within the domain of control of that program. On the other hand, ideas about an algorithm can be communicated to humans without the precision required for execution by using pseudocode, which interleaves natural language with code written in a programming language.

A programming language provides a structured mechanism for defining pieces of data, and the operations or transformations that may be carried out automatically on that data. A programmer uses the abstractions present in the language to represent the concepts involved in a computation. These concepts are represented as a collection of the simplest elements available (called primitives).[67]Programming is the process by which programmers combine these primitives to compose new programs, or adapt existing ones to new uses or a changing environment.

Programs for a computer might be executed in a batch process without human interaction, or a user might type commands in an interactive session of an interpreter. In this case the “commands” are simply programs, whose execution is chained together. When a language can run its commands through an interpreter (such as a Unix shell or other command-line interface), without compiling, it is called a scripting language.[68]

Measuring language usage[edit]

Determining which is the most widely used programming language is difficult since the definition of usage varies by context. One language may occupy the greater number of programmer hours, a different one has more lines of code, and a third may consume the most CPU time. Some languages are very popular for particular kinds of applications. For example, COBOL is still strong in the corporate data center, often on large mainframes;[69][70]Fortran in scientific and engineering applications; Ada 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[71]
  • the number of books sold that teach or describe the language[72]
  • estimates of the number of existing lines of code written in the language – which may underestimate languages not often found in public searches[73]
  • 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, C, C++, Python, C#, JavaScript, VB .NET, R, PHP, and MATLAB.[74]

Dialects, flavors and implementations[edit]

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 and 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 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. As it is common for one language to have several dialects, it can become quite difficult for an inexperienced programmer to find the right documentation. The BASIC programming language has many dialects.

The explosion of Forth dialects led to the saying “If you’ve seen one Forth… you’ve seen one Forth.”

Taxonomies[edit]

There is no overarching classification scheme for programming languages. A given programming language does not usually have a single ancestor language. Languages commonly arise by combining the elements of several predecessor languages with new ideas in circulation at the time. Ideas that originate in one language will diffuse throughout a family of related languages, and then leap suddenly across familial gaps to appear in an entirely different family.

The task is further complicated by the fact that languages can be classified along multiple axes. For example, Java is both an object-oriented language (because it encourages object-oriented organization) and a concurrent language (because it contains built-in constructs for running multiple threads in parallel). Python 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.[75] More refined paradigms include procedural programming, object-oriented programming, functional programming, and logic programming; some languages are hybrids of paradigms or multi-paradigmatic. An assembly language is not so much a paradigm as a direct model of an underlying machine architecture. By purpose, programming languages might be considered general purpose, system programming languages, scripting languages, domain-specific languages, or concurrent/distributed languages (or a combination of these).[76] Some general purpose languages were designed largely with educational goals.[77]

A programming language may also be classified by factors unrelated to programming paradigm. For instance, most programming languages use English language keywords, while a minority do not. Other languages may be classified as being deliberately esoteric or not.

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Further reading[edit]

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Categories
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Object-oriented programming

Object-oriented programming (OOP) is a programming paradigm based on the concept of “objects“, which can contain data, in the form of fields (often known as attributes or properties), and code, in the form of procedures (often known as methods). A feature of objects is an object’s procedures that can access and often modify the data fields of the object with which they are associated (objects have a notion of “this” or “self”). In OOP, computer programs are designed by making them out of objects that interact with one another.[1][2] OOP languages are diverse, but the most popular ones are class-based, meaning that objects are instances of classes, which also determine their types.

Many of the most widely used programming languages (such as C++, Java, Python, etc.) are multi-paradigm and they support object-oriented programming to a greater or lesser degree, typically in combination with imperative, procedural programming. Significant object-oriented languages include
Java,
C++,
C#,
Python,
PHP,
JavaScript,
Ruby,
Perl,
Object Pascal,
Objective-C,
Dart,
Swift,
Scala,
Common Lisp,
MATLAB,
and
Smalltalk.

Features

Object-oriented programming uses objects, but not all of the associated techniques and structures are supported directly in languages that claim to support OOP. The features listed below are common among languages considered to be strongly class- and object-oriented (or multi-paradigm with OOP support), with notable exceptions mentioned.[3][4][5][6]

Shared with non-OOP predecessor languages

Modular programming support provides the ability to group procedures into files and modules for organizational purposes. Modules are namespaced so identifiers in one module will not conflict with a procedure or variable sharing the same name in another file or module.

Objects and classes

Languages that support object-oriented programming (OOP) typically use inheritance for code reuse and extensibility in the form of either classes or prototypes. Those that use classes support two main concepts:

  • Classes – the definitions for the data format and available procedures for a given type or class of object; may also contain data and procedures (known as class methods) themselves, i.e. classes contain the data members and member functions
  • Objects – instances of classes

Objects sometimes correspond to things found in the real world. For example, a graphics program may have objects such as “circle”, “square”, “menu”. An online shopping system might have objects such as “shopping cart”, “customer”, and “product”.[7] Sometimes objects represent more abstract entities, like an object that represents an open file, or an object that provides the service of translating measurements from U.S. customary to metric.

Object-oriented programming is more than just classes and objects; it’s a whole programming paradigm based around [sic] objects (data structures) that contain data fields and methods. It is essential to understand this; using classes to organize a bunch of unrelated methods together is not object orientation.

Junade Ali, Mastering PHP Design Patterns[8]

Each object is said to be an instance of a particular class (for example, an object with its name field set to “Mary” might be an instance of class Employee). Procedures in object-oriented programming are known as methods; variables are also known as fields, members, attributes, or properties. This leads to the following terms:

  • Class variables – belong to the class as a whole; there is only one copy of each one
  • Instance variables or attributes – data that belongs to individual objects; every object has its own copy of each one
  • Member variables – refers to both the class and instance variables that are defined by a particular class
  • Class methods – belong to the class as a whole and have access only to class variables and inputs from the procedure call
  • Instance methods – belong to individual objects, and have access to instance variables for the specific object they are called on, inputs, and class variables

Objects are accessed somewhat like variables with complex internal structure, and in many languages are effectively pointers, serving as actual references to a single instance of said object in memory within a heap or stack. They provide a layer of abstraction which can be used to separate internal from external code. External code can use an object by calling a specific instance method with a certain set of input parameters, read an instance variable, or write to an instance variable. Objects are created by calling a special type of method in the class known as a constructor. A program may create many instances of the same class as it runs, which operate independently. This is an easy way for the same procedures to be used on different sets of data.

Object-oriented programming that uses classes is sometimes called class-based programming, while prototype-based programming does not typically use classes. As a result, a significantly different yet analogous terminology is used to define the concepts of object and instance.

In some languages classes and objects can be composed using other concepts like traits and mixins.

Class-based vs prototype-based

In class-based languages the classes are defined beforehand and the objects are instantiated based on the classes. If two objects apple and orange are instantiated from the class Fruit, they are inherently fruits and it is guaranteed that you may handle them in the same way; e.g. a programmer can expect the existence of the same attributes such as color or sugar_content or is_ripe.

In prototype-based languages the objects are the primary entities. No classes even exist. The prototype of an object is just another object to which the object is linked. Every object has one prototype link (and only one). New objects can be created based on already existing objects chosen as their prototype. You may call two different objects apple and orange a fruit, if the object fruit exists, and both apple and orange have fruit as their prototype. The idea of the fruit class doesn’t exist explicitly, but as the equivalence class of the objects sharing the same prototype. The attributes and methods of the prototype are delegated to all the objects of the equivalence class defined by this prototype. The attributes and methods owned individually by the object may not be shared by other objects of the same equivalence class; e.g. the attribute sugar_content may be unexpectedly not present in apple. Only single inheritance can be implemented through the prototype.

Dynamic dispatch/message passing

It is the responsibility of the object, not any external code, to select the procedural code to execute in response to a method call, typically by looking up the method at run time in a table associated with the object. This feature is known as dynamic dispatch, and distinguishes an object from an abstract data type (or module), which has a fixed (static) implementation of the operations for all instances. If the call variability relies on more than the single type of the object on which it is called (i.e. at least one other parameter object is involved in the method choice), one speaks of multiple dispatch.

A method call is also known as message passing. It is conceptualized as a message (the name of the method and its input parameters) being passed to the object for dispatch.

Encapsulation

Encapsulation is an object-oriented programming concept that binds together the data and functions that manipulate the data, and that keeps both safe from outside interference and misuse. Data encapsulation led to the important OOP concept of data hiding.

If a class does not allow calling code to access internal object data and permits access through methods only, this is a strong form of abstraction or information hiding known as encapsulation. Some languages (Java, for example) let classes enforce access restrictions explicitly, for example denoting internal data with the private keyword and designating methods intended for use by code outside the class with the public keyword. Methods may also be designed public, private, or intermediate levels such as protected (which allows access from the same class and its subclasses, but not objects of a different class). In other languages (like Python) this is enforced only by convention (for example, private methods may have names that start with an underscore). Encapsulation prevents external code from being concerned with the internal workings of an object. This facilitates code refactoring, for example allowing the author of the class to change how objects of that class represent their data internally without changing any external code (as long as “public” method calls work the same way). It also encourages programmers to put all the code that is concerned with a certain set of data in the same class, which organizes it for easy comprehension by other programmers. Encapsulation is a technique that encourages decoupling.

Composition, inheritance, and delegation

Objects can contain other objects in their instance variables; this is known as object composition. For example, an object in the Employee class might contain (either directly or through a pointer) an object in the Address class, in addition to its own instance variables like “first_name” and “position”. Object composition is used to represent “has-a” relationships: every employee has an address, so every Employee object has access to a place to store an Address object (either directly embedded within itself, or at a separate location addressed via a pointer).

Languages that support classes almost always support inheritance. This allows classes to be arranged in a hierarchy that represents “is-a-type-of” relationships. For example, class Employee might inherit from class Person. All the data and methods available to the parent class also appear in the child class with the same names. For example, class Person might define variables “first_name” and “last_name” with method “make_full_name()”. These will also be available in class Employee, which might add the variables “position” and “salary”. This technique allows easy re-use of the same procedures and data definitions, in addition to potentially mirroring real-world relationships in an intuitive way. Rather than utilizing database tables and programming subroutines, the developer utilizes objects the user may be more familiar with: objects from their application domain.[9]

Subclasses can override the methods defined by superclasses. Multiple inheritance is allowed in some languages, though this can make resolving overrides complicated. Some languages have special support for mixins, though in any language with multiple inheritance, a mixin is simply a class that does not represent an is-a-type-of relationship. Mixins are typically used to add the same methods to multiple classes. For example, class UnicodeConversionMixin might provide a method unicode_to_ascii() when included in class FileReader and class WebPageScraper, which don’t share a common parent.

Abstract classes cannot be instantiated into objects; they exist only for the purpose of inheritance into other “concrete” classes which can be instantiated. In Java, the final keyword can be used to prevent a class from being subclassed.

The doctrine of composition over inheritance advocates implementing has-a relationships using composition instead of inheritance. For example, instead of inheriting from class Person, class Employee could give each Employee object an internal Person object, which it then has the opportunity to hide from external code even if class Person has many public attributes or methods. Some languages, like Go do not support inheritance at all.

The “open/closed principle” advocates that classes and functions “should be open for extension, but closed for modification”.

Delegation is another language feature that can be used as an alternative to inheritance.

Polymorphism

Subtyping – a form of polymorphism – is when calling code can be agnostic as to which class in the supported hierarchy it is operating on – the parent class or one of its descendants. Meanwhile, the same operation name among objects in an inheritance hierarchy may behave differently.

For example, objects of type Circle and Square are derived from a common class called Shape. The Draw function for each type of Shape implements what is necessary to draw itself while calling code can remain indifferent to the particular type of Shape is being drawn.

This is another type of abstraction which simplifies code external to the class hierarchy and enables strong separation of concerns.

Open recursion

In languages that support open recursion, object methods can call other methods on the same object (including themselves), typically using a special variable or keyword called this or self. This variable is late-bound; it allows a method defined in one class to invoke another method that is defined later, in some subclass thereof.

History

UML notation for a class. This Button class has variables for data, and functions. Through inheritance a subclass can be created as subset of the Button class. Objects are instances of a class.

Terminology invoking “objects” and “oriented” in the modern sense of object-oriented programming made its first appearance at MIT in the late 1950s and early 1960s. In the environment of the artificial intelligence group, as early as 1960, “object” could refer to identified items (LISP atoms) with properties (attributes);[10][11]Alan Kay was later to cite a detailed understanding of LISP internals as a strong influence on his thinking in 1966.[12]

I thought of objects being like biological cells and/or individual computers on a network, only able to communicate with messages (so messaging came at the very beginning – it took a while to see how to do messaging in a programming language efficiently enough to be useful).

Alan Kay, [12]

Another early MIT example was Sketchpad created by Ivan Sutherland in 1960–61; in the glossary of the 1963 technical report based on his dissertation about Sketchpad, Sutherland defined notions of “object” and “instance” (with the class concept covered by “master” or “definition”), albeit specialized to graphical interaction.[13]
Also, an MIT ALGOL version, AED-0, established a direct link between data structures (“plexes”, in that dialect) and procedures, prefiguring what were later termed “messages”, “methods”, and “member functions”.[14][15]

In the 1960s, object-oriented programming was put into practice with the Simula language, which introduced important concepts that are today an essential part of object-oriented programming, such as class and object, inheritance, and dynamic binding.[16] Simula was also designed to take account of programming and data security. For programming security purposes a detection process was implemented so that through reference counts a last resort garbage collector deleted unused objects in the random-access memory (RAM). But although the idea of data objects had already been established by 1965, data encapsulation through levels of scope for variables, such as private (-) and public (+), were not implemented in Simula because it would have required the accessing procedures to be also hidden.[17]

In 1962, Kristen Nygaard initiated a project for a simulation language at the Norwegian Computing Center, based on his previous use of the Monte Carlo simulation and his work to conceptualise real-world systems. Ole-Johan Dahl formally joined the project and the Simula programming language was designed to run on the Universal Automatic Computer (UNIVAC) 1107. In the early stages Simula was supposed to be a procedure package for the programming language ALGOL 60. Dissatisfied with the restrictions imposed by ALGOL the researchers decided to develop Simula into a fully-fledged programming language, which used the UNIVAC ALGOL 60 compiler. Simula launched in 1964, and was promoted by Dahl and Nygaard throughout 1965 and 1966, leading to increasing use of the programming language in Sweden, Germany and the Soviet Union. In 1968, the language became widely available through the Burroughs B5500 computers, and was later also implemented on the URAL-16 computer. In 1966, Dahl and Nygaard wrote a Simula compiler. They became preoccupied with putting into practice Tony Hoare‘s record class concept, which had been implemented in the free-form, English-like general-purpose simulation language SIMSCRIPT. They settled for a generalised process concept with record class properties, and a second layer of prefixes. Through prefixing a process could reference its predecessor and have additional properties. Simula thus introduced the class and subclass hierarchy, and the possibility of generating objects from these classes. The Simula 1 compiler and a new version of the programming language, Simula 67, was introduced to the wider world through the research paper “Class and Subclass Declarations” at a 1967 conference.[18]

A Simula 67 compiler was launched for the System/360 and System/370 IBM mainframe computers in 1972. In the same year a Simula 67 compiler was launched free of charge for the French CII 10070 and CII Iris 80 mainframe computers. By 1974, the Association of Simula Users had members in 23 different countries. Early 1975 a Simula 67 compiler was released free of charge for the DECsystem-10 mainframe family. By August the same year the DECsystem-10 Simula 67 compiler had been installed at 28 sites, 22 of them in North America. The object-oriented Simula programming language was used mainly by researchers involved with physical modelling, such as models to study and improve the movement of ships and their content through cargo ports.[19]

In the 1970s, the first version of the Smalltalk programming language was developed at Xerox PARC by Alan Kay, Dan Ingalls and Adele Goldberg. Smaltalk-72 included a programming environment and was dynamically typed, and at first was interpreted, not compiled. Smalltalk got noted for its application of object orientation at the language level and its graphical development environment. Smalltalk went through various versions and interest in the language grew.[20] While Smalltalk was influenced by the ideas introduced in Simula 67 it was designed to be a fully dynamic system in which classes could be created and modified dynamically.[21]

In the 1970s, Smalltalk influenced the Lisp community to incorporate object-based techniques that were introduced to developers via the Lisp machine. Experimentation with various extensions to Lisp (such as LOOPS and Flavors introducing multiple inheritance and mixins) eventually led to the Common Lisp Object System, which integrates functional programming and object-oriented programming and allows extension via a Meta-object protocol. In the 1980s, there were a few attempts to design processor architectures that included hardware support for objects in memory but these were not successful. Examples include the Intel iAPX 432 and the Linn Smart Rekursiv.

In 1981, Goldberg edited the August 1981 issue of Byte Magazine, introducing Smalltalk and object-oriented programming to a wider audience. In 1986, the Association for Computing Machinery organised the first Conference on Object-Oriented Programming, Systems, Languages, and Applications (OOPSLA), which was unexpectedly attended by 1,000 people. In the mid-1980s Objective-C was developed by Brad Cox, who had used Smalltalk at ITT Inc., and Bjarne Stroustrup, who had used Simula for his PhD thesis, eventually went to create the object-oriented C++.[20] In 1985, Bertrand Meyer also produced the first design of the Eiffel language. Focused on software quality, Eiffel is a purely object-oriented programming language and a notation supporting the entire software lifecycle. Meyer described the Eiffel software development method, based on a small number of key ideas from software engineering and computer science, in Object-Oriented Software Construction. Essential to the quality focus of Eiffel is Meyer’s reliability mechanism, Design by Contract, which is an integral part of both the method and language.

The TIOBE programming language popularity index graph from 2002 to 2018. In the 2000s the object-oriented Java (blue) and the procedural C (black) competed for the top position.

In the early and mid-1990s object-oriented programming developed as the dominant programming paradigm when programming languages supporting the techniques became widely available. These included Visual FoxPro 3.0,[22][23][24]C++,[25] and Delphi[citation needed]. Its dominance was further enhanced by the rising popularity of graphical user interfaces, which rely heavily upon object-oriented programming techniques. An example of a closely related dynamic GUI library and OOP language can be found in the Cocoa frameworks on Mac OS X, written in Objective-C, an object-oriented, dynamic messaging extension to C based on Smalltalk. OOP toolkits also enhanced the popularity of event-driven programming (although this concept is not limited to OOP).

At ETH Zürich, Niklaus Wirth and his colleagues had also been investigating such topics as data abstraction and modular programming (although this had been in common use in the 1960s or earlier). Modula-2 (1978) included both, and their succeeding design, Oberon, included a distinctive approach to object orientation, classes, and such.

Object-oriented features have been added to many previously existing languages, including Ada, BASIC, Fortran, Pascal, and COBOL. Adding these features to languages that were not initially designed for them often led to problems with compatibility and maintainability of code.

More recently, a number of languages have emerged that are primarily object-oriented, but that are also compatible with procedural methodology. Two such languages are Python and Ruby. Probably the most commercially important recent object-oriented languages are Java, developed by Sun Microsystems, as well as C# and Visual Basic.NET (VB.NET), both designed for Microsoft’s .NET platform. Each of these two frameworks shows, in its own way, the benefit of using OOP by creating an abstraction from implementation. VB.NET and C# support cross-language inheritance, allowing classes defined in one language to subclass classes defined in the other language.

OOP languages

Simula (1967) is generally accepted as being the first language with the primary features of an object-oriented language. It was created for making simulation programs, in which what came to be called objects were the most important information representation. Smalltalk (1972 to 1980) is another early example, and the one with which much of the theory of OOP was developed. Concerning the degree of object orientation, the following distinctions can be made:

OOP in dynamic languages

In recent years, object-oriented programming has become especially popular in dynamic programming languages. Python, PowerShell, Ruby and Groovy are dynamic languages built on OOP principles, while Perl and PHP have been adding object-oriented features since Perl 5 and PHP 4, and ColdFusion since version 6.

The Document Object Model of HTML, XHTML, and XML documents on the Internet has bindings to the popular JavaScript/ECMAScript language. JavaScript is perhaps the best known prototype-based programming language, which employs cloning from prototypes rather than inheriting from a class (contrast to class-based programming). Another scripting language that takes this approach is Lua.

OOP in a network protocol

The messages that flow between computers to request services in a client-server environment can be designed as the linearizations of objects defined by class objects known to both the client and the server. For example, a simple linearized object would consist of a length field, a code point identifying the class, and a data value. A more complex example would be a command consisting of the length and code point of the command and values consisting of linearized objects representing the command’s parameters. Each such command must be directed by the server to an object whose class (or superclass) recognizes the command and is able to provide the requested service. Clients and servers are best modeled as complex object-oriented structures. Distributed Data Management Architecture (DDM) took this approach and used class objects to define objects at four levels of a formal hierarchy:

  • Fields defining the data values that form messages, such as their length, code point and data values.
  • Objects and collections of objects similar to what would be found in a Smalltalk program for messages and parameters.
  • Managers similar to AS/400 objects, such as a directory to files and files consisting of metadata and records. Managers conceptually provide memory and processing resources for their contained objects.
  • A client or server consisting of all the managers necessary to implement a full processing environment, supporting such aspects as directory services, security and concurrency control.

The initial version of DDM defined distributed file services. It was later extended to be the foundation of Distributed Relational Database Architecture (DRDA).

Design patterns

Challenges of object-oriented design are addressed by several approaches. Most common is known as the design patterns codified by Gamma et al.. More broadly, the term “design patterns” can be used to refer to any general, repeatable, solution pattern to a commonly occurring problem in software design. Some of these commonly occurring problems have implications and solutions particular to object-oriented development.

Inheritance and behavioral subtyping

It is intuitive to assume that inheritance creates a semanticis a” relationship, and thus to infer that objects instantiated from subclasses can always be safely used instead of those instantiated from the superclass. This intuition is unfortunately false in most OOP languages, in particular in all those that allow mutable objects. Subtype polymorphism as enforced by the type checker in OOP languages (with mutable objects) cannot guarantee behavioral subtyping in any context. Behavioral subtyping is undecidable in general, so it cannot be implemented by a program (compiler). Class or object hierarchies must be carefully designed, considering possible incorrect uses that cannot be detected syntactically. This issue is known as the Liskov substitution principle.

Gang of Four design patterns

Design Patterns: Elements of Reusable Object-Oriented Software is an influential book published in 1994 by Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides, often referred to humorously as the “Gang of Four”. Along with exploring the capabilities and pitfalls of object-oriented programming, it describes 23 common programming problems and patterns for solving them.
As of April 2007, the book was in its 36th printing.

The book describes the following patterns:

Object-orientation and databases

Both object-oriented programming and relational database management systems (RDBMSs) are extremely common in software today. Since relational databases don’t store objects directly (though some RDBMSs have object-oriented features to approximate this), there is a general need to bridge the two worlds. The problem of bridging object-oriented programming accesses and data patterns with relational databases is known as object-relational impedance mismatch. There are a number of approaches to cope with this problem, but no general solution without downsides.[27] One of the most common approaches is object-relational mapping, as found in IDE languages such as Visual FoxPro and libraries such as Java Data Objects and Ruby on Rails‘ ActiveRecord.

There are also object databases that can be used to replace RDBMSs, but these have not been as technically and commercially successful as RDBMSs.

Real-world modeling and relationships

OOP can be used to associate real-world objects and processes with digital counterparts. However, not everyone agrees that OOP facilitates direct real-world mapping (see Criticism section) or that real-world mapping is even a worthy goal; Bertrand Meyer argues in Object-Oriented Software Construction[28] that a program is not a model of the world but a model of some part of the world; “Reality is a cousin twice removed”. At the same time, some principal limitations of OOP have been noted.[29]
For example, the circle-ellipse problem is difficult to handle using OOP’s concept of inheritance.

However, Niklaus Wirth (who popularized the adage now known as Wirth’s law: “Software is getting slower more rapidly than hardware becomes faster”) said of OOP in his paper, “Good Ideas through the Looking Glass”, “This paradigm closely reflects the structure of systems ‘in the real world’, and it is therefore well suited to model complex systems with complex behaviours”[30] (contrast KISS principle).

Steve Yegge and others noted that natural languages lack the OOP approach of strictly prioritizing things (objects/nouns) before actions (methods/verbs).[31] This problem may cause OOP to suffer more convoluted solutions than procedural programming.[32]

OOP and control flow

OOP was developed to increase the reusability and maintainability of source code.[33] Transparent representation of the control flow had no priority and was meant to be handled by a compiler. With the increasing relevance of parallel hardware and multithreaded coding, developing transparent control flow becomes more important, something hard to achieve with OOP.[34][35][36][37]

Responsibility- vs. data-driven design

Responsibility-driven design defines classes in terms of a contract, that is, a class should be defined around a responsibility and the information that it shares. This is contrasted by Wirfs-Brock and Wilkerson with data-driven design, where classes are defined around the data-structures that must be held. The authors hold that responsibility-driven design is preferable.

SOLID and GRASP guidelines

SOLID is a mnemonic invented by Michael Feathers that stands for and advocates five programming practices:

GRASP (General Responsibility Assignment Software Patterns) is another set of guidelines advocated by Craig Larman.

Criticism

The OOP paradigm has been criticised for a number of reasons, including not meeting its stated goals of reusability and modularity,[38][39] and for overemphasizing one aspect of software design and modeling (data/objects) at the expense of other important aspects (computation/algorithms).[40][41]

Luca Cardelli has claimed that OOP code is “intrinsically less efficient” than procedural code, that OOP can take longer to compile, and that OOP languages have “extremely poor modularity properties with respect to class extension and modification”, and tend to be extremely complex.[38] The latter point is reiterated by Joe Armstrong, the principal inventor of Erlang, who is quoted as saying:[39]

The problem with object-oriented languages is they’ve got all this implicit environment that they carry around with them. You wanted a banana but what you got was a gorilla holding the banana and the entire jungle.

A study by Potok et al. has shown no significant difference in productivity between OOP and procedural approaches.[42]

Christopher J. Date stated that critical comparison of OOP to other technologies, relational in particular, is difficult because of lack of an agreed-upon and rigorous definition of OOP;[43] however, Date and Darwen have proposed a theoretical foundation on OOP that uses OOP as a kind of customizable type system to support RDBMS.[44]

In an article Lawrence Krubner claimed that compared to other languages (LISP dialects, functional languages, etc.) OOP languages have no unique strengths, and inflict a heavy burden of unneeded complexity.[45]

Alexander Stepanov compares object orientation unfavourably to generic programming:[40]

I find OOP technically unsound. It attempts to decompose the world in terms of interfaces that vary on a single type. To deal with the real problems you need multisorted algebras — families of interfaces that span multiple types. I find OOP philosophically unsound. It claims that everything is an object. Even if it is true it is not very interesting — saying that everything is an object is saying nothing at all.

Paul Graham has suggested that OOP’s popularity within large companies is due to “large (and frequently changing) groups of mediocre programmers”. According to Graham, the discipline imposed by OOP prevents any one programmer from “doing too much damage”.[46]

Leo Brodie has suggested a connection between the standalone nature of objects and a tendency to duplicate code[47] in violation of the don’t repeat yourself principle[48] of software development.

Steve Yegge noted that, as opposed to functional programming:[49]

Object Oriented Programming puts the Nouns first and foremost. Why would you go to such lengths to put one part of speech on a pedestal? Why should one kind of concept take precedence over another? It’s not as if OOP has suddenly made verbs less important in the way we actually think. It’s a strangely skewed perspective.

Rich Hickey, creator of Clojure, described object systems as overly simplistic models of the real world. He emphasized the inability of OOP to model time properly, which is getting increasingly problematic as software systems become more concurrent.[41]

Eric S. Raymond, a Unix programmer and open-source software advocate, has been critical of claims that present object-oriented programming as the “One True Solution”, and has written that object-oriented programming languages tend to encourage thickly layered programs that destroy transparency.[50] Raymond compares this unfavourably to the approach taken with Unix and the C programming language.[50]

Rob Pike, a programmer involved in the creation of UTF-8 and Go, has called object-oriented programming “the Roman numerals of computing”[51] and has said that OOP languages frequently shift the focus from data structures and algorithms to types.[52] Furthermore, he cites an instance of a Java professor whose “idiomatic” solution to a problem was to create six new classes, rather than to simply use a lookup table.[53]

Formal semantics

Objects are the run-time entities in an object-oriented system. They may represent a person, a place, a bank account, a table of data, or any item that the program has to handle.

There have been several attempts at formalizing the concepts used in object-oriented programming. The following concepts and constructs have been used as interpretations of OOP concepts:

Attempts to find a consensus definition or theory behind objects have not proven very successful (however, see Abadi & Cardelli, A Theory of Objects[55] for formal definitions of many OOP concepts and constructs), and often diverge widely. For example, some definitions focus on mental activities, and some on program structuring. One of the simpler definitions is that OOP is the act of using “map” data structures or arrays that can contain functions and pointers to other maps, all with some syntactic and scoping sugar on top. Inheritance can be performed by cloning the maps (sometimes called “prototyping”).

Further reading


Categories
blog

C#

C# (pronounced see sharp, like the musical note C♯, but written with the number sign)[b] is a general-purpose, multi-paradigm programming language encompassing strong typing, lexically scoped, imperative, declarative, functional, generic, object-oriented (class-based), and component-oriented programming disciplines.[16] It was developed around 2000 by Microsoft as part of its .NET initiative, and later approved as an international standard by Ecma (ECMA-334) and ISO (ISO/IEC 23270:2018). Mono is the name of the free and open-source project to develop a compiler and runtime for the language. C# is one of the programming languages designed for the Common Language Infrastructure (CLI).

C# was designed by Anders Hejlsberg, and its development team is currently led by Mads Torgersen. The most recent version is 8.0, which was released in 2019 alongside Visual Studio 2019 version 16.3.[17]

Design goals

The Ecma standard lists these design goals for C#:[16]

  • The language is intended to be a simple, modern, general-purpose, object-oriented programming language.
  • The language, and implementations thereof, should provide support for software engineering principles such as strong type checking, array bounds checking, detection of attempts to use uninitialized variables, and automatic garbage collection. Software robustness, durability, and programmer productivity are important.
  • The language is intended for use in developing software components suitable for deployment in distributed environments.
  • Portability is very important for source code and programmers, especially those already familiar with C and C++.
  • Support for internationalization is very important.
  • C# is intended to be suitable for writing applications for both hosted and embedded systems, ranging from the very large that use sophisticated operating systems, down to the very small having dedicated functions.
  • Although C# applications are intended to be economical with regard to memory and processing power requirements, the language was not intended to compete directly on performance and size with C or assembly language

History

During the development of the .NET Framework, the class libraries were originally written using a managed code compiler system called “Simple Managed C” (SMC).[18][19] In January 1999, Anders Hejlsberg formed a team to build a new language at the time called Cool, which stood for “C-like Object Oriented Language”.[20] Microsoft had considered keeping the name “Cool” as the final name of the language, but chose not to do so for trademark reasons. By the time the .NET project was publicly announced at the July 2000 Professional Developers Conference, the language had been renamed C#, and the class libraries and ASP.NET runtime had been ported to C#.

Hejlsberg is C#’s principal designer and lead architect at Microsoft, and was previously involved with the design of Turbo Pascal, Embarcadero Delphi (formerly CodeGear Delphi, Inprise Delphi and Borland Delphi), and Visual J++. In interviews and technical papers he has stated that flaws[21] in most major programming languages (e.g. C++, Java, Delphi, and Smalltalk) drove the fundamentals of the Common Language Runtime (CLR), which, in turn, drove the design of the C# language itself.

James Gosling, who created the Java programming language in 1994, and Bill Joy, a co-founder of Sun Microsystems, the originator of Java, called C# an “imitation” of Java; Gosling further said that “[C# is] sort of Java with reliability, productivity and security deleted.”[22][23] Klaus Kreft and Angelika Langer (authors of a C++ streams book) stated in a blog post that “Java and C# are almost identical programming languages. Boring repetition that lacks innovation,”[24] “Hardly anybody will claim that Java or C# are revolutionary programming languages that changed the way we write programs,” and “C# borrowed a lot from Java – and vice versa. Now that C# supports boxing and unboxing, we’ll have a very similar feature in Java.”[25]
In July 2000, Hejlsberg said that C# is “not a Java clone” and is “much closer to C++” in its design.[26]

Since the release of C# 2.0 in November 2005, the C# and Java languages have evolved on increasingly divergent trajectories, becoming two very different languages. One of the first major departures came with the addition of generics to both languages, with vastly different implementations. C# makes use of reification to provide “first-class” generic objects that can be used like any other class, with code generation performed at class-load time.[27]
Furthermore, C# has added several major features to accommodate functional-style programming, culminating in the LINQ extensions released with C# 3.0 and its supporting framework of lambda expressions, extension methods, and anonymous types.[28] These features enable C# programmers to use functional programming techniques, such as closures, when it is advantageous to their application. The LINQ extensions and the functional imports help developers reduce the amount of boilerplate code that is included in common tasks like querying a database, parsing an xml file, or searching through a data structure, shifting the emphasis onto the actual program logic to help improve readability and maintainability.[29]

C# used to have a mascot called Andy (named after Anders Hejlsberg). It was retired on January 29, 2004.[30]

C# was originally submitted to the ISO subcommittee JTC 1/SC 22 for review,[31] under ISO/IEC 23270:2003,[32] was withdrawn and was then approved under ISO/IEC 23270:2006.[33]

Name

Microsoft first used the name C# in 1988 for a variant of the C language designed for incremental compilation.[34] That project was not completed but the name lives on.

The name “C sharp” was inspired by the musical notation where a sharp indicates that the written note should be made a semitone higher in pitch.[35]
This is similar to the language name of C++, where “++” indicates that a variable should be incremented by 1 after being evaluated. The sharp symbol also resembles a ligature of four “+” symbols (in a two-by-two grid), further implying that the language is an increment of C++.[36]

Due to technical limitations of display (standard fonts, browsers, etc.) and the fact that the sharp symbol (

U+266F

MUSIC SHARP SIGN (HTML )) is not present on most keyboard layouts, the number sign (U+0023 # NUMBER SIGN (HTML #)) was chosen to approximate the sharp symbol in the written name of the programming language.[37]
This convention is reflected in the ECMA-334 C# Language Specification.[16]

The “sharp” suffix has been used by a number of other .NET languages that are variants of existing languages, including J# (a .NET language also designed by Microsoft that is derived from Java 1.1), A# (from Ada), and the functional programming language F#.[38] The original implementation of Eiffel for .NET was called Eiffel#,[39] a name retired since the full Eiffel language is now supported. The suffix has also been used for libraries, such as Gtk# (a .NET wrapper for GTK+ and other GNOME libraries) and Cocoa# (a wrapper for Cocoa).

Versions

Version Language specification Date .NET Framework Visual Studio
Ecma ISO/IEC Microsoft
Version C# 1.0 December 2002 April 2003 January 2002 January 2002 .NET Framework 1.0 Visual Studio .NET 2002
Version C# 1.1
C# 1.2
October 2003 April 2003 .NET Framework 1.1 Visual Studio .NET 2003
Version C# 2.0 June 2006 September 2006 September 2005[c] November 2005 .NET Framework 2.0
.NET Framework 3.0
Visual Studio 2005
Visual Studio 2008
Version C# 3.0 None August 2007 November 2007 .NET Framework 2.0 (Except LINQ)[40]

.NET Framework 3.0 (Except LINQ)[40]
.NET Framework 3.5

Visual Studio 2008
Version C# 4.0 April 2010 April 2010 .NET Framework 4 Visual Studio 2010
Version C# 5.0 December 2017 December 2018 June 2013 August 2012 .NET Framework 4.5 Visual Studio 2012
Visual Studio 2013
Version C# 6.0 None Draft July 2015 .NET Framework 4.6
.NET Core 1.0
.NET Core 1.1
Visual Studio 2015
Version C# 7.0 Specification proposal March 2017 .NET Framework 4.7 Visual Studio 2017 version 15.0
Version C# 7.1 Specification proposal August 2017 .NET Core 2.0 Visual Studio 2017 version 15.3[41]
Version C# 7.2 Specification proposal November 2017 Visual Studio 2017 version 15.5[42]
Version C# 7.3 Specification proposal May 2018 .NET Core 2.1
.NET Core 2.2
.NET Framework 4.8
Visual Studio 2017 version 15.7[42]
Version C# 8 Specification proposal September 2019 .NET Core 3.0 Visual Studio 2019 version 16.3[42]

New features

C# 2.0
C# 3.0
C# 4.0
  • Dynamic binding[46]
  • Named and optional arguments[46]
  • Generic co- and contravariance[46]
  • Embedded interop types (“NoPIA”)[46]
C# 5.0[47]
C# 6.0
  • Compiler-as-a-service (Roslyn)
  • Import of static type members into namespace[49]
  • Exception filters[49]
  • Await in catch/finally blocks[49]
  • Auto property initializers[49]
  • Default values for getter-only properties[49]
  • Expression-bodied members[49]
  • Null propagator (null-conditional operator, succinct null checking)[49]
  • String interpolation[49]
  • nameof operator[49]
  • Dictionary initializer[49]
C# 7.0[50][51]
  • Inline out variable declaration
  • Pattern matching
  • Tuple types and tuple literals
  • Deconstruction
  • Local functions
  • Digit separators
  • Binary literals
  • Ref returns and locals
  • Generalized async return types
  • Expression bodied constructors and finalizers
  • Expression bodied getters and setters
  • Throw can also be used as expression
C# 7.1[52]
  • Async main
  • Default literal expressions
  • Inferred tuple element names
C# 7.2[53]
  • Reference semantics with value types
  • Non-trailing named arguments
  • Leading underscores in numeric literals
  • private protected access modifier
C# 7.3[54]
  • Accessing fixed fields without pinning
  • Reassigning ref local variables
  • Using initializers on stackalloc arrays
  • Using fixed statements with any type that supports a pattern
  • Using additional generic constraints
C# 8.0[55]
  • readonly struct members
  • default interface members
  • switch expressions
  • Property, Tuple, and positional patterns
  • using declarations
  • static local functions
  • Disposable ref struct
  • Nullable reference types
  • Indices and Ranges
  • Null-coalescing assignment
  • Async Streams

Syntax

The core syntax of C# language is similar to that of other C-style languages such as C, C++ and Java. In particular:

Distinguishing features

Some notable features of C# that distinguish it from C, C++, and Java where noted, are:

Portability

By design, C# is the programming language that most directly reflects the underlying Common Language Infrastructure (CLI).[56] Most of its intrinsic types correspond to value-types implemented by the CLI framework. However, the language specification does not state the code generation requirements of the compiler: that is, it does not state that a C# compiler must target a Common Language Runtime, or generate Common Intermediate Language (CIL), or generate any other specific format. Theoretically, a C# compiler could generate machine code like traditional compilers of C++ or Fortran.

Typing

C# supports strongly typed implicit variable declarations with the keyword var, and implicitly typed arrays with the keyword new[] followed by a collection initializer.

C# supports a strict Boolean data type, bool. Statements that take conditions, such as while and if, require an expression of a type that implements the true operator, such as the Boolean type. While C++ also has a Boolean type, it can be freely converted to and from integers, and expressions such as if (a) require only that a is convertible to bool, allowing a to be an int, or a pointer. C# disallows this “integer meaning true or false” approach, on the grounds that forcing programmers to use expressions that return exactly bool can prevent certain types of programming mistakes such as if (a = b) (use of assignment = instead of equality ==).

C# is more type safe than C++. The only implicit conversions by default are those that are considered safe, such as widening of integers. This is enforced at compile-time, during JIT, and, in some cases, at runtime. No implicit conversions occur between Booleans and integers, nor between enumeration members and integers (except for literal 0, which can be implicitly converted to any enumerated type). Any user-defined conversion must be explicitly marked as explicit or implicit, unlike C++ copy constructors and conversion operators, which are both implicit by default.

C# has explicit support for covariance and contravariance in generic types, unlike C++ which has some degree of support for contravariance simply through the semantics of return types on virtual methods.

Enumeration members are placed in their own scope.

The C# language does not allow for global variables or functions. All methods and members must be declared within classes. Static members of public classes can substitute for global variables and functions.

Local variables cannot shadow variables of the enclosing block, unlike C and C++.

Metaprogramming

Metaprogramming via C# attributes is part of the language. Many of these attributes duplicate the functionality of GCC’s and VisualC++’s platform-dependent preprocessor directives.

Methods and functions

A method in C# is a member of a class that can be invoked as a function (a sequence of instructions), rather than the mere value-holding capability of a class property. As in other syntactically similar languages, such as C++ and ANSI C, the signature of a method is a declaration comprising in order: any optional scope modifier keywords (such as private), the explicit specification of its return type (such as int, or the keyword void if no value is returned), the name of the method, and finally, a parenthesized sequence of comma-separated parameter specifications, each consisting of a parameter’s type, its formal name and optionally, a default value to be used whenever none is provided. Certain specific kinds of methods, such as those that simply get or set a class property by return value or assignment, do not require a full signature, but in the general case, the definition of a class includes the full signature declaration of its methods.

Like C++, and unlike Java, C# programmers must use the scope modifier keyword virtual to allow methods to be overridden by subclasses.[57]

Extension methods in C# allow programmers to use static methods as if they were methods from a class’s method table, allowing programmers to add methods to an object that they feel should exist on that object and its derivatives.

The type dynamic allows for run-time method binding, allowing for JavaScript-like method calls and run-time object composition.

C# has support for strongly-typed function pointers via the keyword delegate. Like the Qt framework’s pseudo-C++ signal and slot, C# has semantics specifically surrounding publish-subscribe style events, though C# uses delegates to do so.

C# offers Java-like synchronized method calls, via the attribute [MethodImpl(MethodImplOptions.Synchronized)], and has support for mutually-exclusive locks via the keyword lock.

Property

C# provides properties as syntactic sugar for a common pattern in which a pair of methods, accessor (getter) and mutator (setter) encapsulate operations on a single attribute of a class. No redundant method signatures[definition needed] for the getter/setter implementations need be written, and the property may be accessed using attribute syntax rather than more verbose method calls.

Namespace

A C# namespace provides the same level of code isolation as a Java package or a C++ namespace, with very similar rules and features to a package. Namespaces can be imported with the “using” syntax.[58]

Memory access

In C#, memory address pointers can only be used within blocks specifically marked as unsafe, and programs with unsafe code need appropriate permissions to run. Most object access is done through safe object references, which always either point to a “live” object or have the well-defined null value; it is impossible to obtain a reference to a “dead” object (one that has been garbage collected), or to a random block of memory. An unsafe pointer can point to an instance of an ‘unmanaged’ value type that does not contain any references to garbage-collected objects, array, string, or a block of stack-allocated memory. Code that is not marked as unsafe can still store and manipulate pointers through the System.IntPtr type, but it cannot dereference them.

Managed memory cannot be explicitly freed; instead, it is automatically garbage collected. Garbage collection addresses the problem of memory leaks by freeing the programmer of responsibility for releasing memory that is no longer needed.

Exception

Checked exceptions are not present in C# (in contrast to Java). This has been a conscious decision based on the issues of scalability and versionability.[59]

Polymorphism

Unlike C++, C# does not support multiple inheritance, although a class can implement any number of interfaces. This was a design decision by the language’s lead architect to avoid complication and simplify architectural requirements throughout CLI. When implementing multiple interfaces that contain a method with the same signature, i. e. two methods with the same name and taking parameters of the same type in the same order, C# allows implementing each method depending on which interface that method is being called through or, like Java, allows implementing the method once, and having that be the one invocation on a call through any of the class’s interfaces.

However, unlike Java, C# supports operator overloading. Only the most commonly overloaded operators in C++ may be overloaded in C#.

Language Integrated Query (LINQ)

C# has the ability to utilize LINQ through the .NET Framework. A developer can query any IEnumerable object, XML documents, an ADO.NET dataset, and a SQL database.[60] Using LINQ in C# brings advantages like Intellisense support, strong filtering capabilities, type safety with compile error checking ability, and consistency for querying data over a variety of sources.[61] There are several different language structures that can be utilized with C# with LINQ and they are query expressions, lambda expressions, anonymous types, implicitly typed variables, extension methods, and object initializers.[62]

Functional programming

Though primarily an imperative language, C# 2.0 offered limited support for functional programming through first-class functions and closures in the form of anonymous delegates. C# 3.0 expanded support for functional programming with the introduction of a lightweight syntax for lambda expressions, extension methods (an affordance for modules), and a list comprehension syntax in the form of a “query comprehension” language. C# 7.0 adds features typically found in functional languages like tuples and pattern matching.[63]

Common type system

C# has a unified type system. This unified type system is called Common Type System (CTS).[64]

A unified type system implies that all types, including primitives such as integers, are subclasses of the System.Object class. For example, every type inherits a ToString() method.

Categories of data types

CTS separates data types into two categories:[64]

  1. Reference types
  2. Value types

Instances of value types do not have referential identity nor referential comparison semantics – equality and inequality comparisons for value types compare the actual data values within the instances, unless the corresponding operators are overloaded. Value types are derived from System.ValueType, always have a default value, and can always be created and copied. Some other limitations on value types are that they cannot derive from each other (but can implement interfaces) and cannot have an explicit default (parameterless) constructor. Examples of value types are all primitive types, such as int (a signed 32-bit integer), float (a 32-bit IEEE floating-point number), char (a 16-bit Unicode code unit), and System.DateTime (identifies a specific point in time with nanosecond precision). Other examples are enum (enumerations) and struct (user defined structures).

In contrast, reference types have the notion of referential identity – each instance of a reference type is inherently distinct from every other instance, even if the data within both instances is the same. This is reflected in default equality and inequality comparisons for reference types, which test for referential rather than structural equality, unless the corresponding operators are overloaded (such as the case for System.String). In general, it is not always possible to create an instance of a reference type, nor to copy an existing instance, or perform a value comparison on two existing instances, though specific reference types can provide such services by exposing a public constructor or implementing a corresponding interface (such as ICloneable or IComparable). Examples of reference types are object (the ultimate base class for all other C# classes), System.String (a string of Unicode characters), and System.Array (a base class for all C# arrays).

Both type categories are extensible with user-defined types.

Boxing and unboxing

Boxing is the operation of converting a value-type object into a value of a corresponding reference type.[64] Boxing in C# is implicit.

Unboxing is the operation of converting a value of a reference type (previously boxed) into a value of a value type.[64] Unboxing in C# requires an explicit type cast. A boxed object of type T can only be unboxed to a T (or a nullable T).[65]

Example:

int foo = 42;         // Value type.
object bar = foo;     // foo is boxed to bar.
int foo2 = (int)bar;  // Unboxed back to value type.

Libraries

The C# specification details a minimum set of types and class libraries that the compiler expects to have available. In practice, C# is most often used with some implementation of the Common Language Infrastructure (CLI), which is standardized as ECMA-335 Common Language Infrastructure (CLI).

In addition to the standard CLI specifications, there are many commercial and community class libraries that build on top of the .NET framework libraries to provide additional functionality.[66]

Examples

The following is a very simple C# program, a version of the classic “Hello world” example:

using System;

class Program
{
    public static void Main(string[] args)
    {
        Console.WriteLine("Hello, world!");
    }
}

This code will display this text in the console window:

Hello, world!

Each line has a purpose:

using System;

The above line imports all types in the System namespace. For example, the Console class used later in the source code is defined in the System namespace, meaning it can be used without supplying the full name of the type (which includes the namespace).

class Program

Above is a class definition. Everything between the following pair of braces describes Program.

static void Main()

This declares the class member method where the program begins execution. The .NET runtime calls the Main method. (Note: Main may also be called from elsewhere, like any other method, e.g. from another method of Program.) The static keyword makes the method accessible without an instance of Program. Each console application’s Main entry point must be declared static. Otherwise, the program would require an instance, but any instance would require a program. To avoid that irresolvable circular dependency, C# compilers processing console applications (like that above) report an error, if there is no static Main method. The void keyword declares that Main has no return value.

Console.WriteLine("Hello, world!");

This line writes the output. Console is a static class in the System namespace. It provides an interface to the standard input, output, and error streams for console applications. The program calls the Console method WriteLine, which displays on the console a line with the argument, the string "Hello, world!".

A GUI example:

using System;
using System.Windows.Forms;

class Program
{
    static void Main()
    {
        MessageBox.Show("Hello, World!");
        Console.WriteLine("Is almost the same argument!");
    }
}

This example is similar to the previous example, except that it generates a dialog box that contains the message “Hello, World!” instead of writing it to the console.

Another useful library is the System.Drawing library, which is used to programmatically draw images. For example:

using System;
using System.Drawing;

public class Example
{
    public static Image img;

    public static void Main()
    {
        img = Image.FromFile("Image.png");
    }
}

This will create an image that is identical to that stored in “Image.png”.

Standardization and licensing

In August 2001, Microsoft Corporation, Hewlett-Packard and Intel Corporation co-sponsored the submission of specifications for C# as well as the Common Language Infrastructure (CLI) to the standards organization Ecma International.
In December 2001, ECMA released ECMA-334 C# Language Specification. C# became an ISO standard in 2003 (ISO/IEC 23270:2003 – Information technology — Programming languages — C#). ECMA had previously adopted equivalent specifications as the 2nd edition of C#, in December 2002.

In June 2005, ECMA approved edition 3 of the C# specification, and updated ECMA-334. Additions included partial classes, anonymous methods, nullable types, and generics (somewhat similar to C++ templates).

In July 2005, ECMA submitted to ISO/IEC JTC 1, via the latter’s Fast-Track process, the standards and related TRs. This process usually takes 6–9 months.

The C# language definition and the CLI are standardized under ISO and Ecma standards that provide reasonable and non-discriminatory licensing protection from patent claims.

Microsoft has agreed not to sue open source developers for violating patents in non-profit projects for the part of the framework that is covered by the OSP.[67] Microsoft has also agreed not to enforce patents relating to Novell products against Novell’s paying customers[68] with the exception of a list of products that do not explicitly mention C#, .NET or Novell’s implementation of .NET (The Mono Project).[69] However, Novell maintains that Mono does not infringe any Microsoft patents.[70] Microsoft has also made a specific agreement not to enforce patent rights related to the Moonlight browser plugin, which depends on Mono, provided it is obtained through Novell.[71]

Implementations

Microsoft is leading the development of the open-source reference C# compiler and set of tools, previously codenamed “Roslyn“. The compiler, which is entirely written in managed code (C#), has been opened up and functionality surfaced as APIs. It is thus enabling developers to create refactoring and diagnostics tools.[4][72]

Other C# compilers (some of which include an implementation of the Common Language Infrastructure and .NET class libraries):

  • The Mono project provides an open-source C# compiler, a complete open-source implementation of the Common Language Infrastructure including the required framework libraries as they appear in the ECMA specification, and a nearly complete implementation of the Microsoft proprietary .NET class libraries up to .NET 3.5. As of Mono 2.6, no plans exist to implement WPF; WF is planned for a later release; and there are only partial implementations of LINQ to SQL and WCF.[73]
  • The DotGNU project (now discontinued) also provided an open-source C# compiler, a nearly complete implementation of the Common Language Infrastructure including the required framework libraries as they appear in the ECMA specification, and subset of some of the remaining Microsoft proprietary .NET class libraries up to .NET 2.0 (those not documented or included in the ECMA specification, but included in Microsoft’s standard .NET Framework distribution).
  • Microsoft’s Shared Source Common Language Infrastructure, codenamed “Rotor”, provides a shared source implementation of the CLR runtime and a C# compiler licensed for educational and research use only, and a subset of the required Common Language Infrastructure framework libraries in the ECMA specification (up to C# 2.0, and supported on Windows XP only).
  • Xamarin provides tools to develop cross-platform applications for common mobile and desktop operating systems, using C# as a codebase and compiling to native code.

Mono is a common choice for game engines due to its cross-platform nature. The Unity game engine uses Mono C# as its primary scripting language. The Godot game engine has implemented an optional Mono C# module thanks to a donation of $24,000 from Microsoft.[74]

Notes

Further reading

Categories
blog

Perl

Perl is a family of two high-level, general-purpose, interpreted, dynamic programming languages. “Perl” refers to Perl 5, but from 2000 to 2019 it also referred to its redesigned “sister language”, Perl 6, before the latter’s name was officially changed to Raku in October 2019.[8][9]

Though Perl is not officially an acronym,[10] there are various backronyms in use, including “Practical Extraction and Reporting Language”.[11] Perl was originally developed by Larry Wall in 1987 as a general-purpose Unix scripting language to make report processing easier.[12] Since then, it has undergone many changes and revisions. Raku, which began as a redesign of Perl 5 in 2000, eventually evolved into a separate language. Both languages continue to be developed independently by different development teams and liberally borrow ideas from one another.

The Perl languages borrow features from other programming languages including C, shell script (sh), AWK, and sed;[13] Wall also alludes to BASIC and Lisp in the introduction to Learning Perl (Schwartz & Christiansen) and so on.[14] They provide text processing facilities without the arbitrary data-length limits of many contemporary Unix command line tools,[15] facilitating manipulation of text files. Perl 5 gained widespread popularity in the late 1990s as a CGI scripting language, in part due to its unsurpassed regular expression and string parsing abilities.[16][17][18][19]

In addition to CGI, Perl 5 is used for system administration, network programming, finance, bioinformatics, and other applications, such as for GUIs. It has been nicknamed “the Swiss Army chainsaw of scripting languages” because of its flexibility and power,[20] and also its ugliness.[21] In 1998, it was also referred to as the “duct tape that holds the Internet together,” in reference to both its ubiquitous use as a glue language and its perceived inelegance.[22]

History

Early versions

Larry Wall began work on Perl in 1987, while working as a programmer at Unisys[15], and released version 1.0 to the comp.sources.misc newsgroup on December 18, 1987[23]. The language expanded rapidly over the next few years.

Perl 2, released in 1988, featured a better regular expression engine. Perl 3, released in 1989, added support for binary data streams.

Originally, the only documentation for Perl was a single lengthy man page. In 1991, Programming Perl, known to many Perl programmers as the “Camel Book” because of its cover, was published and became the de facto reference for the language. At the same time, the Perl version number was bumped to 4, not to mark a major change in the language but to identify the version that was well documented by the book.

Early Perl 5

Perl 4 went through a series of maintenance releases, culminating in Perl 4.036 in 1993, whereupon Wall abandoned Perl 4 to begin work on Perl 5. Initial design of Perl 5 continued into 1994. The perl5-porters mailing list was established in May 1994 to coordinate work on porting Perl 5 to different platforms. It remains the primary forum for development, maintenance, and porting of Perl 5.[24]

Perl 5.000 was released on October 17, 1994.[25] It was a nearly complete rewrite of the interpreter, and it added many new features to the language, including objects, references, lexical (my) variables, and modules. Importantly, modules provided a mechanism for extending the language without modifying the interpreter. This allowed the core interpreter to stabilize, even as it enabled ordinary Perl programmers to add new language features. Perl 5 has been in active development since then.

Perl 5.001 was released on March 13, 1995. Perl 5.002 was released on February 29, 1996 with the new prototypes feature. This allowed module authors to make subroutines that behaved like Perl builtins. Perl 5.003 was released June 25, 1996, as a security release.

One of the most important events in Perl 5 history took place outside of the language proper and was a consequence of its module support. On October 26, 1995, the Comprehensive Perl Archive Network (CPAN) was established as a repository for the Perl language and Perl modules; as of May 2017, it carries over 185,178 modules in 35,190 distributions, written by more than 13,071 authors, and is mirrored worldwide at more than 245 locations.[26]

Perl 5.004 was released on May 15, 1997, and included, among other things, the UNIVERSAL package, giving Perl a base object to which all classes were automatically derived and the ability to require versions of modules. Another significant development was the inclusion of the CGI.pm module,[27] which contributed to Perl’s popularity as a CGI scripting language.[28]

Perl 5.004 also added support for Microsoft Windows and several other operating systems.[27]

Perl 5.005 was released on July 22, 1998. This release included several enhancements to the regex engine, new hooks into the backend through the B::* modules, the qr// regex quote operator, a large selection of other new core modules, and added support for several more operating systems, including BeOS.[29]

2000–present

Major version Latest update
Old version, no longer maintained: 5.005 2004-02-23[30]
Old version, no longer maintained: 5.6 2003-11-15[30]
Old version, no longer maintained: 5.8 2008-12-14[30]
Old version, no longer maintained: 5.10 2009-08-23[30]
Old version, no longer maintained: 5.12 2012-11-10[30]
Old version, no longer maintained: 5.14 2013-03-10[30]
Old version, no longer maintained: 5.16 2013-03-11[30]
Old version, no longer maintained: 5.18 2014-10-02[30]
Old version, no longer maintained: 5.20 2015-09-12[30]
Old version, no longer maintained: 5.22 2017-07-15[30]
Old version, no longer maintained: 5.24 2018-04-14[30]
Old version, no longer maintained: 5.26 2018-11-29[30]
Older version, yet still maintained: 5.28 2019-04-19[30]
Current stable version: 5.30 2019-05-22[30]
Future release: 5.32 2020-05

Legend:
Old version
Older version, still maintained
Current stable version
Latest preview version
Future release

Perl 5.6 was released on March 22, 2000. Major changes included 64-bit support, Unicode string representation, support for files over 2 GiB, and the “our” keyword.[31][32] When developing Perl 5.6, the decision was made to switch the versioning scheme to one more similar to other open source projects; after 5.005_63, the next version became 5.5.640, with plans for development versions to have odd numbers and stable versions to have even numbers.

In 2000, Wall put forth a call for suggestions for a new version of Perl from the community. The process resulted in 361 RFC (request for comments) documents that were to be used in guiding development of Perl 6. In 2001,[33] work began on the “Apocalypses” for Perl 6, a series of documents meant to summarize the change requests and present the design of the next generation of Perl. They were presented as a digest of the RFCs, rather than a formal document. At this point, Perl 6 existed only as a description of a language.

Perl 5.8 was first released on July 18, 2002, and had nearly yearly updates since then. Perl 5.8 improved Unicode support, added a new I/O implementation, added a new thread implementation, improved numeric accuracy, and added several new modules.[34] As of 2013 this version still remains the most popular version of Perl and is used by Red Hat 5, Suse 10, Solaris 10, HP-UX 11.31 and AIX 5.

In 2004, work began on the “Synopses” – documents that originally summarized the Apocalypses, but which became the specification for the Perl 6 language. In February 2005, Audrey Tang began work on Pugs, a Perl 6 interpreter written in Haskell.[35] This was the first concerted effort towards making Perl 6 a reality. This effort stalled in 2006.[36]

On December 18, 2007, the 20th anniversary of Perl 1.0, Perl 5.10.0 was released. Perl 5.10.0 included notable new features, which brought it closer to Perl 6. These included a switch statement (called “given”/”when”), regular expressions updates, and the smart match operator[clarification needed], “~~”.[37][38]
Around this same time, development began in earnest on another implementation of Perl 6 known as Rakudo Perl, developed in tandem with the Parrot virtual machine. As of November 2009, Rakudo Perl has had regular monthly releases and now is the most complete implementation of Perl 6.

A major change in the development process of Perl 5 occurred with Perl 5.11; the development community has switched to a monthly release cycle of development releases, with a yearly schedule of stable releases. By that plan, bugfix point releases will follow the stable releases every three months.

On April 12, 2010, Perl 5.12.0 was released. Notable core enhancements include new package NAME VERSION syntax, the Yada Yada operator (intended to mark placeholder code that is not yet implemented), implicit strictures, full Y2038 compliance, regex conversion overloading, DTrace support, and Unicode 5.2.[39] On January 21, 2011, Perl 5.12.3 was released; it contains updated modules and some documentation changes.[40] Version 5.12.4 was released on June 20, 2011. The latest version of that branch, 5.12.5, was released on November 10, 2012.

On May 14, 2011, Perl 5.14 was released. JSON support is built-in as of 5.14.0.[41] The latest version of that branch, 5.14.4, was released on March 10, 2013.

On May 20, 2012, Perl 5.16 was released. Notable new features include the ability to specify a given version of Perl that one wishes to emulate, allowing users to upgrade their version of Perl, but still run old scripts that would normally be incompatible.[42] Perl 5.16 also updates the core to support Unicode 6.1.[42]

On May 18, 2013, Perl 5.18 was released. Notable new features include the new dtrace hooks, lexical subs, more CORE:: subs, overhaul of the hash for security reasons, support for Unicode 6.2.[43]

On May 27, 2014, Perl 5.20 was released. Notable new features include subroutine signatures, hash slices/new slice syntax, postfix dereferencing (experimental), Unicode 6.3, rand() using consistent random number generator.[44]

Some observers credit the release of Perl 5.10 with the start of the Modern Perl movement.[45] In particular, this phrase describes a style of development that embraces the use of the CPAN, takes advantage of recent developments in the language, and is rigorous about creating high quality code.[46] While the book “Modern Perl”[47] may be the most visible standard-bearer of this idea, other groups such as the Enlightened Perl Organization[48] have taken up the cause.

In late 2012 and 2013, several projects for alternative implementations for Perl 5 started: Perl5 in Perl6 by the Rakudo Perl team,[49]moe by Stevan Little and friends,[50]p2[51] by the Perl11 team under Reini Urban, gperl by goccy,[52] and rperl a kickstarter project led by Will Braswell and affiliated with the Perll11 project.[53]

PONIE

PONIE is an acronym for Perl On New Internal Engine. The PONIE Project existed from 2003 until 2006 and was to be a bridge between Perl 5 and Perl 6. It was an effort to rewrite the Perl 5 interpreter to run on Parrot, the Perl 6 virtual machine. The goal was to ensure the future of the millions of lines of Perl 5 code at thousands of companies around the world.[54]

The PONIE project ended in 2006 and is no longer being actively developed. Some of the improvements made to the Perl 5 interpreter as part of PONIE were folded into that project.[55]

Name

Perl was originally named “Pearl”. Wall wanted to give the language a short name with positive connotations; he claims that he considered every three- and four-letter word in the dictionary. He also considered naming it after his wife Gloria. Wall discovered the existing PEARL programming language before Perl’s official release and changed the spelling of the name.[56]

When referring to the language, the name is normally capitalized (Perl) as a proper noun. When referring to the interpreter program itself, the name is often uncapitalized (perl) because most Unix-like file systems are case-sensitive. Before the release of the first edition of Programming Perl, it was common to refer to the language as perl; Randal L. Schwartz, however, capitalized the language’s name in the book to make it stand out better when typeset. This case distinction was subsequently documented as canonical.[57]

The name is occasionally expanded as Practical Extraction and Report Language, but this is a backronym.[58] Other expansions have been suggested as equally canonical, including Wall’s own Pathologically Eclectic Rubbish Lister which is in the manual page for perl.[59] Indeed, Wall claims that the name was intended to inspire many different expansions.[60]

Camel symbol

The Camel symbol used by O’Reilly Media

Programming Perl, published by O’Reilly Media, features a picture of a dromedary camel on the cover and is commonly called the “Camel Book”.[61] This image of a camel has become an unofficial symbol of Perl as well as a general hacker emblem, appearing on T-shirts and other clothing items.

O’Reilly owns the image as a trademark but licenses it for non-commercial use, requiring only an acknowledgement and a link to www.perl.com. Licensing for commercial use is decided on a case by case basis.[62] O’Reilly also provides “Programming Republic of Perl” logos for non-commercial sites and “Powered by Perl” buttons for any site that uses Perl.[62]

Onion symbol

The onion logo used by The Perl Foundation

The Perl Foundation owns an alternative symbol, an onion, which it licenses to its subsidiaries, Perl Mongers, PerlMonks, Perl.org, and others.[63] The symbol is a visual pun on pearl onion.[64]

Raptor symbol

Alternative Perl 5 Logo

Sebastian Riedel, the creator of Mojolicious, has created a logo depicting a raptor dinosaur, which is available under a CC-SA License, Version 4.0.[65] The logo is being remixed and used in different places and is symbolising Perl 5. The analogue of the raptor comes from a series of talks given by Matt S Trout beginning in 2010.[66] The talks were aimed at being more Perl 5 community-centric, in a period where Perl 6 was a hot topic.

Overview

According to Wall, Perl has two slogans. The first is “There’s more than one way to do it,” commonly known as TMTOWTDI. The second slogan is “Easy things should be easy and hard things should be possible”.[15]

Features

The overall structure of Perl derives broadly from C. Perl is procedural in nature, with variables, expressions, assignment statements, brace-delimited blocks, control structures, and subroutines.

Perl also takes features from shell programming. All variables are marked with leading sigils, which allow variables to be interpolated directly into strings. However, unlike the shell, Perl uses sigils on all accesses to variables, and unlike most other programming languages that use sigils, the sigil doesn’t denote the type of the variable but the type of the expression. So for example, to access a list of values in a hash, the sigil for an array (“@”) is used, not the sigil for a hash (“%”).
Perl also has many built-in functions that provide tools often used in shell programming (although many of these tools are implemented by programs external to the shell) such as sorting, and calling operating system facilities.

Perl takes lists from Lisp, hashes (“associative arrays”) from AWK, and regular expressions from sed. These simplify and facilitate many parsing, text-handling, and data-management tasks. Also shared with Lisp are the implicit return of the last value in a block, and the fact that all statements have a value, and thus are also expressions and can be used in larger expressions themselves.

Perl 5 added features that support complex data structures, first-class functions (that is, closures as values), and an object-oriented programming model. These include references, packages, class-based method dispatch, and lexically scoped variables, along with compiler directives (for example, the strict pragma). A major additional feature introduced with Perl 5 was the ability to package code as reusable modules. Wall later stated that “The whole intent of Perl 5’s module system was to encourage the growth of Perl culture rather than the Perl core.”[67]

All versions of Perl do automatic data-typing and automatic memory management. The interpreter knows the type and storage requirements of every data object in the program; it allocates and frees storage for them as necessary using reference counting (so it cannot deallocate circular data structures without manual intervention). Legal type conversions — for example, conversions from number to string — are done automatically at run time; illegal type conversions are fatal errors.

Design

The design of Perl can be understood as a response to three broad trends in the computer industry: falling hardware costs, rising labor costs, and improvements in compiler technology. Many earlier computer languages, such as Fortran and C, aimed to make efficient use of expensive computer hardware. In contrast, Perl was designed so that computer programmers could write programs more quickly and easily.

Perl has many features that ease the task of the programmer at the expense of greater CPU and memory requirements. These include automatic memory management; dynamic typing; strings, lists, and hashes; regular expressions; introspection; and an eval() function. Perl follows the theory of “no built-in limits,”[61] an idea similar to the Zero One Infinity rule.

Wall was trained as a linguist, and the design of Perl is very much informed by linguistic principles. Examples include Huffman coding (common constructions should be short), good end-weighting (the important information should come first), and a large collection of language primitives. Perl favors language constructs that are concise and natural for humans to write, even where they complicate the Perl interpreter.

Perl’s syntax reflects the idea that “things that are different should look different.”[68] For example, scalars, arrays, and hashes have different leading sigils. Array indices and hash keys use different kinds of braces. Strings and regular expressions have different standard delimiters. This approach can be contrasted with a language such as Lisp, where the same basic syntax, composed of simple and universal symbolic expressions, is used for all purposes.

Perl does not enforce any particular programming paradigm (procedural, object-oriented, functional, or others) or even require the programmer to choose among them.

There is a broad practical bent to both the Perl language and the community and culture that surround it. The preface to Programming Perl begins: “Perl is a language for getting your job done.”[15] One consequence of this is that Perl is not a tidy language. It includes many features, tolerates exceptions to its rules, and employs heuristics to resolve syntactical ambiguities. Because of the forgiving nature of the compiler, bugs can sometimes be hard to find. Perl’s function documentation remarks on the variant behavior of built-in functions in list and scalar contexts by saying, “In general, they do what you want, unless you want consistency.”[69]

No written specification or standard for the Perl language exists for Perl versions through Perl 5, and there are no plans to create one for the current version of Perl. There has been only one implementation of the interpreter, and the language has evolved along with it. That interpreter, together with its functional tests, stands as a de facto specification of the language. Perl 6, however, started with a specification,[70] and several projects[71] aim to implement some or all of the specification.

Applications

Perl has many and varied applications, compounded by the availability of many standard and third-party modules.

Perl has chiefly been used to write CGI scripts: large projects written in Perl include cPanel, Slash, Bugzilla, RT, TWiki, and Movable Type; high-traffic websites that use Perl extensively include Priceline.com, Craigslist,[72]IMDb,[73]LiveJournal, DuckDuckGo,[74][75]Slashdot and Ticketmaster.
It is also an optional component of the popular LAMP technology stack for Web development, in lieu of PHP or Python. Perl is used extensively as a system programming language in the Debian GNU/Linux distribution.[76]

Perl is often used as a glue language, tying together systems and interfaces that were not specifically designed to interoperate, and for “data munging,”[77] that is, converting or processing large amounts of data for tasks such as creating reports. In fact, these strengths are intimately linked. The combination makes Perl a popular all-purpose language for system administrators, particularly because short programs, often called “one-liner programs,” can be entered and run on a single command line.

Perl code can be made portable across Windows and Unix; such code is often used by suppliers of software (both COTS and bespoke) to simplify packaging and maintenance of software build- and deployment-scripts.

Graphical user interfaces (GUIs) may be developed using Perl. For example, Perl/Tk and wxPerl are commonly used to enable user interaction with Perl scripts. Such interaction may be synchronous or asynchronous, using callbacks to update the GUI.

Implementation

Perl is implemented as a core interpreter, written in C, together with a large collection of modules, written in Perl and C. As of 2010, the interpreter is 150,000 lines of C code and compiles to a 1 MB executable on typical machine architectures. Alternatively, the interpreter can be compiled to a link library and embedded in other programs. There are nearly 500 modules in the distribution, comprising 200,000 lines of Perl and an additional 350,000 lines of C code (much of the C code in the modules consists of character encoding tables).

The interpreter has an object-oriented architecture. All of the elements of the Perl language—scalars, arrays, hashes, coderefs, file handles—are represented in the interpreter by C structs. Operations on these structs are defined by a large collection of macros, typedefs, and functions; these constitute the Perl C API. The Perl API can be bewildering to the uninitiated, but its entry points follow a consistent naming scheme, which provides guidance to those who use it.

The life of a Perl interpreter divides broadly into a compile phase and a run phase.[78] In Perl, the phases are the major stages in the interpreter’s life-cycle. Each interpreter goes through each phase only once, and the phases follow in a fixed sequence.

Most of what happens in Perl’s compile phase is compilation, and most of what happens in Perl’s run phase is execution, but there are significant exceptions. Perl makes important use of its capability to execute Perl code during the compile phase. Perl will also delay compilation into the run phase. The terms that indicate the kind of processing that is actually occurring at any moment are compile time and run time. Perl is in compile time at most points during the compile phase, but compile time may also be entered during the run phase. The compile time for code in a string argument passed to the eval built-in occurs during the run phase. Perl is often in run time during the compile phase and spends most of the run phase in run time. Code in BEGIN blocks executes at run time but in the compile phase.

At compile time, the interpreter parses Perl code into a syntax tree. At run time, it executes the program by walking the tree. Text is parsed only once, and the syntax tree is subject to optimization before it is executed, so that execution is relatively efficient. Compile-time optimizations on the syntax tree include constant folding and context propagation, but peephole optimization is also performed.

Perl has a Turing-complete grammar because parsing can be affected by run-time code executed during the compile phase.[79] Therefore, Perl cannot be parsed by a straight Lex/Yacc lexer/parser combination. Instead, the interpreter implements its own lexer, which coordinates with a modified GNU bison parser to resolve ambiguities in the language.

It is often said that “Only perl can parse Perl,”[80] meaning that only the Perl interpreter (perl) can parse the Perl language (Perl), but even this is not, in general, true. Because the Perl interpreter can simulate a Turing machine during its compile phase, it would need to decide the halting problem in order to complete parsing in every case. It is a long-standing result that the halting problem is undecidable, and therefore not even perl can always parse Perl. Perl makes the unusual choice of giving the user access to its full programming power in its own compile phase. The cost in terms of theoretical purity is high, but practical inconvenience seems to be rare.

Other programs that undertake to parse Perl, such as source-code analyzers and auto-indenters, have to contend not only with ambiguous syntactic constructs but also with the undecidability of Perl parsing in the general case. Adam Kennedy‘s PPI project focused on parsing Perl code as a document (retaining its integrity as a document), instead of parsing Perl as executable code (that not even Perl itself can always do). It was Kennedy who first conjectured that “parsing Perl suffers from the ‘halting problem‘,”[81] which was later proved.[82]

Perl is distributed with over 250,000 functional tests for core Perl language and over 250,000 functional tests for core modules. These run as part of the normal build process and extensively exercise the interpreter and its core modules. Perl developers rely on the functional tests to ensure that changes to the interpreter do not introduce software bugs; additionally, Perl users who see that the interpreter passes its functional tests on their system can have a high degree of confidence that it is working properly.

Availability

Perl is dual licensed under both the Artistic License 1.0[4][5] and the GNU General Public License.[6] Distributions are available for most operating systems. It is particularly prevalent on Unix and Unix-like systems, but it has been ported to most modern (and many obsolete) platforms. With only six[citation needed] reported exceptions, Perl can be compiled from source code on all POSIX-compliant, or otherwise-Unix-compatible platforms.[83]

Because of unusual changes required for the classic Mac OS environment, a special port called MacPerl was shipped independently.[84]

The Comprehensive Perl Archive Network carries a complete list of supported platforms with links to the distributions available on each.[85] CPAN is also the source for publicly available Perl modules that are not part of the core Perl distribution.

Windows

Users of Microsoft Windows typically install one of the native binary distributions of Perl for Win32, most commonly Strawberry Perl or ActivePerl. Compiling Perl from source code under Windows is possible, but most installations lack the requisite C compiler and build tools. This also makes it difficult to install modules from the CPAN, particularly those that are partially written in C.

ActivePerl is a closed source distribution from ActiveState that has regular releases that track the core Perl releases.[86] The distribution also includes the Perl package manager (PPM),[87] a popular tool for installing, removing, upgrading, and managing the use of common Perl modules. Included also is PerlScript, a Windows Script Host (WSH) engine implementing the Perl language. Visual Perl is an ActiveState tool that adds Perl to the Visual Studio .NET development suite. A VBScript to Perl converter, as well as a Perl compiler for Windows, and converters of awk and sed to Perl have also been produced by this company and included on the ActiveState CD for Windows, which includes all of their distributions plus the Komodo IDE and all but the first on the Unix/Linux/Posix variant thereof in 2002 and subsequently.[88]

Strawberry Perl is an open source distribution for Windows. It has had regular, quarterly releases since January 2008, including new modules as feedback and requests come in. Strawberry Perl aims to be able to install modules like standard Perl distributions on other platforms, including compiling XS modules.

The Cygwin emulation layer is another way of running Perl under Windows. Cygwin provides a Unix-like environment on Windows, and both Perl and CPAN are available as standard pre-compiled packages in the Cygwin setup program. Since Cygwin also includes gcc, compiling Perl from source is also possible.

A perl executable is included in several Windows Resource kits in the directory with other scripting tools.

Implementations of Perl come with the MKS Toolkit, Interix (the base of earlier implementations of Windows Services for Unix, and UWIN.

Database interfaces

Perl’s text-handling capabilities can be used for generating SQL queries; arrays, hashes, and automatic memory management make it easy to collect and process the returned data. For example, in Tim Bunce’s Perl DBI application programming interface (API), the arguments to the API can be the text of SQL queries; thus it is possible to program in multiple languages at the same time (e.g., for generating a Web page using HTML, JavaScript, and SQL in a here document). The use of Perl variable interpolation to programmatically customize each of the SQL queries, and the specification of Perl arrays or hashes as the structures to programmatically hold the resulting data sets from each SQL query, allows a high-level mechanism for handling large amounts of data for post-processing by a Perl subprogram.[89]
In early versions of Perl, database interfaces were created by relinking the interpreter with a client-side database library. This was sufficiently difficult that it was done for only a few of the most-important and most widely used databases, and it restricted the resulting perl executable to using just one database interface at a time.

In Perl 5, database interfaces are implemented by Perl DBI modules. The DBI (Database Interface) module presents a single, database-independent interface to Perl applications, while the DBD (Database Driver) modules handle the details of accessing some 50 different databases; there are DBD drivers for most ANSI SQL databases.

DBI provides caching for database handles and queries, which can greatly improve performance in long-lived execution environments such as mod perl,[90] helping high-volume systems avert load spikes as in the Slashdot effect.

In modern Perl applications, especially those written using web frameworks such as Catalyst, the DBI module is often used indirectly via object-relational mappers such as DBIx::Class, Class::DBI or Rose::DB::Object that generate SQL queries and handle data transparently to the application author.

Comparative performance

The Computer Language Benchmarks Game compares the performance of implementations of typical programming problems in several programming languages.[91] The submitted Perl implementations typically perform toward the high end of the memory-usage spectrum and give varied speed results. Perl’s performance in the benchmarks game is typical for interpreted languages.[92]

Large Perl programs start more slowly than similar programs in compiled languages because perl has to compile the source every time it runs. In a talk at the YAPC::Europe 2005 conference and subsequent article “A Timely Start,” Jean-Louis Leroy found that his Perl programs took much longer to run than expected because the perl interpreter spent significant time finding modules within his over-large include path.[93] Unlike Java, Python, and Ruby, Perl has only experimental support for pre-compiling.[94] Therefore, Perl programs pay this overhead penalty on every execution. The run phase of typical programs is long enough that amortized startup time is not substantial, but benchmarks that measure very short execution times are likely to be skewed due to this overhead.

A number of tools have been introduced to improve this situation. The first such tool was Apache’s mod perl, which sought to address one of the most-common reasons that small Perl programs were invoked rapidly: CGI Web development. ActivePerl, via Microsoft ISAPI, provides similar performance improvements.

Once Perl code is compiled, there is additional overhead during the execution phase that typically isn’t present for programs written in compiled languages such as C or C++. Examples of such overhead include bytecode interpretation, reference-counting memory management, and dynamic type-checking.

Optimizing

Because Perl is an interpreted language, it can give problems when efficiency is critical; in such situations, the most critical routines can be written in other languages (such as C), which can be connected to Perl via simple Inline modules or the more complex but flexible XS mechanism.[95]

Perl 5

Perl 5, the language usually referred to as “Perl”, continues to be actively developed. Perl 5.12.0 was released in April 2010 with some new features influenced by the design of Perl 6,[39][96] followed by Perl 5.14.1 (released on June 17, 2011), Perl 5.16.1 (released on August 9, 2012.[97]), and Perl 5.18.0 (released on May 18, 2013). Perl 5 development versions are released on a monthly basis, with major releases coming out once per year.[98]

The relative proportion of Internet searches for “Perl programming”, as compared with similar searches for other programming languages, steadily declined from about 10% in 2005 to about 2% in 2011, to just over 1% in 2019.[99]

Perl 6

Camelia, the logo for the Perl 6 project.[100]

At the 2000 Perl Conference, Jon Orwant made a case for a major new language-initiative.[101] This led to a decision to begin work on a redesign of the language, to be called Perl 6. Proposals for new language features were solicited from the Perl community at large, which submitted more than 300 RFCs.

Wall spent the next few years digesting the RFCs and synthesizing them into a coherent framework for Perl 6. He presented his design for Perl 6 in a series of documents called “apocalypses” – numbered to correspond to chapters in Programming Perl. As of January 2011, the developing specification of Perl 6 is encapsulated in design documents called Synopses – numbered to correspond to Apocalypses.[102]

Thesis work by Bradley M. Kuhn, overseen by Wall, considered the possible use of the Java virtual machine as a runtime for Perl.[103] Kuhn’s thesis showed this approach to be problematic. In 2001, it was decided that Perl 6 would run on a cross-language virtual machine called Parrot. This will mean that other languages targeting the Parrot will gain native access to CPAN, allowing some level of cross-language development.

In 2005, Audrey Tang created the Pugs project, an implementation of Perl 6 in Haskell. This acted as, and continues to act as, a test platform for the Perl 6 language (separate from the development of the actual implementation) – allowing the language designers to explore. The Pugs project spawned an active Perl/Haskell cross-language community centered around the freenode #perl6 IRC channel. Many functional programming influences were absorbed by the Perl 6 design team.

In 2012, Perl 6 development was centered primarily around two compilers:[104]

  1. Rakudo, an implementation running on the Parrot virtual machine and the Java virtual machine.[105]
  2. Niecza, which targets the Common Language Runtime.

In 2013, MoarVM (“Metamodel On A Runtime”), a C language-based virtual machine designed primarily for Rakudo was announced.[106]

In October 2019, Perl 6 was renamed to Raku.[107]

As of 2017 only the Rakudo implementation and MoarVM are under active development, and other virtual machines, such as the Java Virtual Machine and JavaScript are supported.[108]

Perl community

Perl’s culture and community has developed alongside the language itself. Usenet was the first public venue in which Perl was introduced, but over the course of its evolution, Perl’s community was shaped by the growth of broadening Internet-based services including the introduction of the World Wide Web. The community that surrounds Perl was, in fact, the topic of Wall’s first “State of the Onion” talk.[109]

State of the Onion

State of the Onion is the name for Wall’s yearly keynote-style summaries on the progress of Perl and its community. They are characterized by his hallmark humor, employing references to Perl’s culture, the wider hacker culture, Wall’s linguistic background, sometimes his family life, and occasionally even his Christian background.[110]

Each talk is first given at various Perl conferences and is eventually also published online.

Perl pastimes

JAPHs
In email, Usenet, and message board postings, “Just another Perl hacker” (JAPH) programs are a common trend, originated by Randal L. Schwartz, one of the earliest professional Perl trainers.[111] In the parlance of Perl culture, Perl programmers are known as Perl hackers, and from this derives the practice of writing short programs to print out the phrase “Just another Perl hacker”. In the spirit of the original concept, these programs are moderately obfuscated and short enough to fit into the signature of an email or Usenet message. The “canonical” JAPH as developed by Schwartz includes the comma at the end, although this is often omitted.[112]
Perl golf
Perl “golf” is the pastime of reducing the number of characters (key “strokes”) used in a Perl program to the bare minimum, much in the same way that golf players seek to take as few shots as possible in a round. The phrase’s first use[113] emphasized the difference between pedestrian code meant to teach a newcomer and terse hacks likely to amuse experienced Perl programmers, an example of the latter being JAPHs that were already used in signatures in Usenet postings and elsewhere. Similar stunts had been an unnamed pastime in the language APL in previous decades. The use of Perl to write a program that performed RSA encryption prompted a widespread and practical interest in this pastime.[114] In subsequent years, the term “code golf” has been applied to the pastime in other languages.[115] A Perl Golf Apocalypse was held at Perl Conference 4.0 in Monterey, California in July 2000.
Obfuscation
As with C, obfuscated code competitions were a well known pastime in the late 1990s. The Obfuscated Perl Contest was a competition held by The Perl Journal from 1996 to 2000 that made an arch virtue of Perl’s syntactic flexibility. Awards were given for categories such as “most powerful”—programs that made efficient use of space—and “best four-line signature” for programs that fit into four lines of 76 characters in the style of a Usenet signature block.[116]
Poetry
Perl poetry is the practice of writing poems that can be compiled as legal Perl code, for example the piece known as Black Perl. Perl poetry is made possible by the large number of English words that are used in the Perl language. New poems are regularly submitted to the community at PerlMonks.[117]

Perl on IRC

There are a number of IRC channels that offer support for the language and some modules.

IRC Network Channels
irc.freenode.net #perl #perl6 #cbstream #perlcafe #poe
irc.perl.org #moose #poe #catalyst #dbix-class #perl-help #distzilla #epo #corehackers #sdl #win32 #toolchain #padre #dancer
irc.slashnet.org #perlmonks
irc.oftc.net #perl
irc.efnet.net #perlhelp
irc.rizon.net #perl
irc.debian.org #debian-perl (packaging Perl modules for Debian)

CPAN Acme

There are also many examples of code written purely for entertainment on the CPAN. Lingua::Romana::Perligata, for example, allows writing programs in Latin.[118] Upon execution of such a program, the module translates its source code into regular Perl and runs it.

The Perl community has set aside the “Acme” namespace for modules that are fun in nature (but its scope has widened to include exploratory or experimental code or any other module that is not meant to ever be used in production). Some of the Acme modules are deliberately implemented in amusing ways. This includes Acme::Bleach, one of the first modules in the Acme:: namespace,[119] which allows the program’s source code to be “whitened” (i.e., all characters replaced with whitespace) and yet still work.

Example code

In older versions of Perl, one would write the Hello World program as:

print "Hello, World!n";

Here is a more complex Perl program, that counts down the seconds up to a given threshold:

#!/usr/bin/perl
use strict;
use warnings;
use IO::Handle;

my ( $remaining, $total );

$remaining = $total = shift(@ARGV);

STDOUT->autoflush(1);

while ( $remaining ) {
    printf ( "Remaining %s/%s r", $remaining--, $total );
    sleep 1;
}

print "n";

The perl interpreter can also be used for one-off scripts on the command line. The following example (as invoked from an sh-compatible shell, such as Bash) translates the string “Bob” in all files ending with .txt in the current directory to “Robert”:

$ perl -i.bak -lp -e 's/Bob/Robert/g' *.txt

Criticism

Perl has been referred to as “line noise” by some programmers who claim its syntax makes it a write-only language. The earliest such mention was in the first edition of the book Learning Perl, a Perl 4 tutorial book written by Randal L. Schwartz,[120] in the first chapter of which he states: “Yes, sometimes Perl looks like line noise to the uninitiated, but to the seasoned Perl programmer, it looks like checksummed line noise with a mission in life.”[121] He also stated that the accusation that Perl is a write-only language could be avoided by coding with “proper care”.[121] The Perl overview document perlintro states that the names of built-in “magic” scalar variables “look like punctuation or line noise”.[122] However, the English module provides both long and short English alternatives. perlstyle document states that line noise in regular expressions could be mitigated using the /x modifier to add whitespace.[123]

According to the Perl 6 FAQ, Perl 6 was designed to mitigate “the usual suspects” that elicit the “line noise” claim from Perl 5 critics, including the removal of “the majority of the punctuation variables” and the sanitization of the regex syntax.[124] The Perl 6 FAQ also states that what is sometimes referred to as Perl’s line noise is “the actual syntax of the language” just as gerunds and prepositions are a part of the English language.[124] In a December 2012 blog posting, despite claiming that “Rakudo Perl 6 has failed and will continue to fail unless it gets some adult supervision”, chromatic stated that the design of Perl 6 has a “well-defined grammar” as well as an “improved type system, a unified object system with an intelligent metamodel, metaoperators, and a clearer system of context that provides for such niceties as pervasive laziness”.[125] He also stated that “Perl 6 has a coherence and a consistency that Perl 5 lacks.”[125]

Further reading


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Free Pascal

Free Pascal Compiler (FPC) is a compiler for the closely related programming-language dialects Pascal and Object Pascal. It is free software released under the GNU General Public License, with exception clauses that allow static linking against its runtime libraries and packages for any purpose in combination with any other software license.

It supports its own Object Pascal dialect, as well as the dialects of several other Pascal family compilers to a certain extent, including those of Turbo Pascal, Delphi, and some historical Macintosh compilers. The dialect is selected on a per-unit (module) basis, and more than one dialect can be used per program.

It follows a write once, compile anywhere philosophy and is available for many CPU architectures and operating systems (see Targets). It supports inline assembly language and includes an internal assembler capable of parsing several dialects such as AT&T and Intel style.

Separate projects exist to facilitate developing cross-platform graphical user interface (GUI) applications, the most prominent one being the Lazarus integrated development environment (IDE).

Supported dialects

Initially, Free Pascal adopted the de facto standard dialect of Pascal programmers – Borland Pascal – but later on adopted Delphi. From version 2.0 on, Delphi compatibility has been continuously implemented or improved.

The project has a compilation mode concept, and the developers made it clear that they would incorporate working patches for the standardized dialects of the American National Standards Institute (ANSI) and International Organization for Standardization (ISO) to create a standards-compliant mode.

A small effort has been made to support some of the Apple Pascal syntax to ease interfacing to the Classic Mac OS and macOS. Since the Apple dialect implements some standard Pascal features that Turbo Pascal and Delphi omit, Free Pascal is a bit more ISO-compatible than these.

The 2.2.x release series did not significantly change the dialect objectives beyond roughly Delphi 7 level syntax, instead aiming for closer compatibility. A notable exception to this was the addition of support for generics to Free Pascal in version 2.2.0, several years before they were supported in any capacity by Delphi.

As of 2011, several Delphi 2006-specific features were added in the development branch, and some of the starting work for the features new in Delphi 2009 (most notably the addition of the UnicodeString type) was completed. The development branch also features an Objective-Pascal extension for Objective-C (Cocoa) interfacing.

As of version 2.7.1, Free Pascal implemented basic ISO Pascal mode, though many things such as Get and Put procedure and file-buffer variable concept for file handling were still absent.

As of version 3.0.0, ISO Pascal mode is fairly complete, with one remaining bug that has since been fixed in the trunk branch. It has been able to compile standardpascal.org’s P5 ISO Pascal compiler with no changes.

History

Early years

Free Pascal was created when Borland clarified that Borland Pascal development for DOS would stop with version 7, to be replaced by a Windows-only product, which later became Delphi.

Student Florian Paul Klämpfl began developing his own compiler written in the Turbo Pascal dialect and produced 32-bit code for the GO32v1 DOS extender, which was used and developed by the DJ’s GNU Programming Platform (DJGPP) project at that time.

Originally, the compiler was a 16-bit DOS executable compiled by Turbo Pascal. After two years, the compiler was able to compile itself and became a 32-bit executable.

Expansion

The initial 32-bit compiler was published on the Internet, and the first contributors joined the project. Later, a Linux port was created by Michael van Canneyt, five years before the Borland Kylix compiler became available.

The DOS port was adapted for use in OS/2 using the Eberhard Mattes eXtender (EMX) which made OS/2 the second supported compiling target. As well as Florian Klämpfl the original author, Daniël Mantione also contributed significantly to make this happen, providing the original port of the run-time library to OS/2 and EMX. The compiler improved gradually, and the DOS version migrated to the GO32v2 extender. This culminated in release 0.99.5, which was much more widely used than prior versions, and was the last release aiming only for Turbo Pascal compliance; later releases added a Delphi compatibility mode. This release was also ported to systems using Motorola 68000 family (m68k) processors.

With release 0.99.8 the Win32 target was added, and a start was made with incorporating some Delphi features. Stabilizing for a non-beta release began, and version 1.0 was released in July 2000. The 1.0.x series was widely used, in business and education. For the 1.0.x releases, the port to 68k CPU was redone, and the compiler produced stable code for several 68k Unix-like and AmigaOS operating systems.

Version 2

During the stabilization of what would become 1.0.x, and also when porting to the Motorola 68k systems, it was clear that the design of the code generator was far too limited in many aspects. The principal problems were that adding processors meant rewriting the code generator, and that the register allocation was based on the principle of always keeping three free registers between building blocks, which was inflexible and difficult to maintain.

For these reasons, the 1.1.x series branched off from the 1.0.x main branch in December 1999. At first, changes were mostly clean-ups and rewrite-redesigns to all parts of the compiler. The code generator and register allocator were also rewritten. Any remaining missing Delphi compatibility was added.

The work on 1.1.x continued slowly but steadily. In late 2003, a working PowerPC port became available, followed by an ARM port in summer 2004, a SPARC port in fall 2004, and an x86-64-AMD64 port in early 2004, which made the compiler available for a 64-bit platform.

In November 2003, a first beta release of the 1.1.x branch was packaged and numbered 1.9.0. These were quickly followed by versions 1.9.2 and 1.9.4; the latter introduced OS X support. The work continued with version 1.9.6 (January 2005), 1.9.8 (late February 2005), 2.0.0 (May 2005), 2.0.2 (December 2005), and 2.0.4 (August 2006).

Version 2.2.x

In 2006, some of the major reworks planned for 2.2, such as the rewrite of the unit system, had still not begun, and it was decided to instead start stabilizing the already implemented features.

Some of the motives for this roadmap change were the needs of the Lazarus integrated development environment project, particularly the internal linker, support for Win64, Windows CE, and OS X on x86, and related features like DWARF. After betas 2.1.2 and 2.1.4, version 2.2.0 was released in September 2007, followed by version 2.2.2 in August 2008 and version 2.2.4 in March 2009.

The 2.2.x series vastly improved support for the ActiveX and Component Object Model (COM) interface, and Object Linking and Embedding (OLE), though bugs were still being found. The delegation to interface using the implements keyword was partly implemented, but was not complete as of March 2011.[1] Library support for ActiveX was also improved.

Another major feature was the internal linker for Win32, Win64, and Windows CE, which greatly improveď linking time and memory use, and make the compile-link-run cycle in Lazarus much faster. The efficiency for smart-linking, or dead code elimination, was also improved.

Minor new features included improved DWARF (2/3) debug format support, and optimizations such as tail recursion, omission of unneeded stack frames and register-based common subexpression elimination (CSE) optimization. A first implementation of generic programming (generics) support also became available, but only experimentally.

Version 2.4.x

The 2.4.x release series had a less clear set of goals than earlier releases. The unit system rewrite was postponed again, and the branch that became 2.4 was created to keep risky commits from 2.2 to stabilize it. Mostly these risky commits were more involved improvements to the new platforms, Mac PowerPC 64, Mac x86-64, iPhone, and many fixes to the ARM and x86-64 architectures in general, as well as DWARF.

Other compiler improvements included whole program optimization (WPO) and devirtualization and ARM embedded-application binary interface (EABI) support.

Later, during the 2.2 cycle, a more Delphi-like resource support (based on special sections in the binary instead of Pascal constants) was added. This feature, direly needed by Lazarus, became the main highlight of the branch.

Other more minor additions were a memory manager that improved heap manager performance in threaded environments, small improvements in Delphi compatibility such as OleVariant, and improvements in interface delegation.

On January 1, 2010, Free Pascal 2.4.0 was released, followed on November 13, 2010, by bug fix release 2.4.2, with support for for..in loops, sealed and abstract classes, and other changes.[2]

Version 2.6.x

In January 2012, Free Pascal 2.6 was released. This first version from the 2.6 release series also supported Objective Pascal on OS X and iOS targets and implemented many small improvements and bug fixes. In February 2013, FPC 2.6.2 was released. It contained NetBSD and OpenBSD releases for the first time since 1.0.10, based on fresh ports. In March 2014, the last point release in the 2.6 series, 2.6.4, was launched, featuring mostly database (fcl-db) updates.

Version 3.0.x

Version 3.0.0 was released on November 25, 2015 and was the first major release since January 1, 2012.
It contains many new language features: FPC New Features 3.0

Later releases

Version 3.0.2 was released on February 15, 2017 and includes bug fixes and minor compiler updates.
Version 3.0.4 was released on November 28, 2017.

It includes many language improvements over previous versions like an internal linker for Executable and Linkable Format (ELF), Arm AARCH64 for iOS and Linux, a revived i8086 platform, extended libraries and much more.

Targets

Processor architecture Operating system, device Version 3.0.0 – 3.3.1 (Trunk) Version 2.6.2 Version 2.6.0 Version 2.4.4 Version 2.4.2 Version 2.4.0 Version 2.2.4 Version 2.0.x Version 1.0.x
i386 DOS (GO32v2 extender) Yes Yes Yes Yes Yes Yes Yes Yes Yes
FreeBSD Yes Yes Yes Yes Yes Yes Yes Yes Yes
OpenBSD Yes Yes No No No No No No Yes
NetBSD Yes Yes No No No No No No Yes
Linux Yes Yes Yes Yes Yes Yes Yes Yes Yes
macOS Yes Yes Yes Yes Yes Yes Yes No No
OS/2 Yes Yes Yes Yes Yes Yes Yes Yes Yes
Windows Yes Yes Yes Yes Yes Yes Yes Yes Yes
Windows CE Yes Yes Yes Yes Yes Yes No No No
BeOS Yes Yes Yes Yes Yes Yes Yes Yes Yes
Haiku Yes Yes Yes Yes Yes Yes No No No
NetWare Yes Yes Yes Yes Yes Yes Yes Yes No
Solaris Yes Yes Yes Yes Yes No No No Yes
iPhone Sim Yes Yes Yes No No No No No No
QNX Neutrino No No No No No No No No Yes
Android Yes Yes No No No No No No No
AROS Yes No No No No No No No No
x86-64 FreeBSD Yes Yes Yes Yes Yes No No No No
OpenBSD Yes Yes Unknown Unknown Unknown Unknown Unknown Unknown Unknown
NetBSD Yes Yes Unknown Unknown Unknown Unknown Unknown Unknown Unknown
Linux Yes Yes Yes Yes Yes Yes Yes Unknown No
macOS Yes Yes Yes Yes Yes Yes No No No
Windows Yes Yes Yes Yes Yes Yes No No No
iPhone Sim Yes Yes Yes No No No No No No
AROS Yes Yes Yes Yes Yes No No No No
DragonFly BSD Yes Yes Yes Yes Yes No No No No
Solaris Yes Yes Yes Yes Yes No No No No
Haiku Yes No No No No No No No No
ARM iOS Yes Yes Yes Yes Yes Yes No No No
Game Boy Advance Yes Yes Yes Yes Yes Yes No No No
Nintendo DS Yes Yes Yes Yes Yes Yes No No No
Linux Yes Yes Yes Yes Yes Yes Yes Unknown No
Windows CE Yes Yes Yes Yes Yes Yes Yes Unknown No
Android Yes Yes No No No No No No No
Embedded Yes Yes No No No No No No No
AArch64 Linux Yes Yes No No No No No No No
iOS Yes Yes No No No No No No No
Android Yes No No No No No No No No
AVR Embedded Yes No No No No No No No No
PowerPC Linux Yes Yes Yes Yes Yes Yes Yes Yes No
macOS Yes Yes Yes Yes Yes Yes Yes Yes No
Classic Mac OS Yes Yes Yes Yes No No Yes Yes No
MorphOS Yes Yes Yes Yes Unknown Unknown Unknown Yes No
AIX Yes Yes Yes No No No No No No
Wii Yes Yes Yes Yes No No No No No
PowerPC 64-bit Linux Yes Yes Yes Yes Yes Yes Yes No No
macOS Yes Yes Yes Yes Yes Yes No No No
AIX Yes Yes Yes No No No No No No
SPARC Solaris Yes Yes Yes Yes Yes No No No No
NetBSD Yes Yes Yes Yes Yes No No No No
Embedded Yes Yes Yes Yes Yes No No No No
Linux Yes Yes Yes Yes Yes No No No No
SPARC64 Linux Yes Yes Yes No No No No No No
RISC-V Embedded Yes No No No No No No No No
RISC-V64 Embedded Yes No No No No No No No No
Java virtual machine Java Yes No No No No No No No No
Android Yes No No No No No No No No
MIPS (BE and LE) Linux Yes No No No No No No No No
Embedded Yes No No No No No No No No
8086 (16-bit) DOS Yes No No No No No No No No
Win16 Yes No No No No No No No No
Embedded Yes No No No No No No No No
m68k Linux Yes No No No No No No No Yes
NetBSD Yes No No No No No No No Yes
AmigaOS Yes No No No No No No No Yes
Atari TOS Yes No No No No No No No Yeslimited cross-compiler only
Palm OS Yes No No No No No No No Unknown

Free Pascal also supports byte code generation for the Java Virtual Machine as of version 3.0.0 and targets both Oracle’s Java and Google’s Android JVM,[3] although Object Pascal syntax is not fully supported. Free Pascal 3.0.0 also supports ARMHF platforms like the Raspberry Pi, including ARMV6-EABIHF running on Raspbian. Work on 64-bit ARM has resulted in support for iOS in 3.0.0 as well. A native ARM Android target has been added, ending the formerly hacked ARM Linux target to generate native ARM libraries for Android. This makes porting Lazarus applications to Android (using Custom Drawn Interface[4]) easier. Since FPC 2.6.2, OpenBSD and NetBSD are supported on IA32 and X86_64 architectures. A new target embedded has been added for usage without OS (ARM Cortex M and MIPS mainly). With InstantFPC it is possible to run Pascal programs, which are translated just in time, as Unix scripts or CGI back-end.

Integrated development environments

Like most modern compilers, Free Pascal can be used with an integrated development environment (IDE). Besides independent IDEs there are also plugins to various existing IDEs

Free Pascal IDE in Linux

  • Free Pascal has its own text-mode IDE resembling Turbo Pascal’s IDE. It is made using the Free Vision framework (also included with Free Pascal), a Turbo Vision clone. In addition to many features of the Turbo Pascal IDE, it has code completion and support for multiple help file formats (HTML, Microsoft Compiled HTML Help (CHM), Information Presentation Facility (IPF). Instead of using command line tools, the IDE uses its own embedded compiler, based on the same source as the command line compiler and debugger (using libgdb or GDBMI) to provide its functionality.
  • Lazarus is the most popular IDE used by Free Pascal programmers. It looks and feels similar to the Delphi IDE, and can be used to create console and graphical applications, Windows services, daemons, and web applications. Lazarus provides a cross-platform user interface framework, called Lazarus Component Library (LCL). Graphical applications created with LCL can be ported to another platform via recompiling or cross compiling.
  • Dev-Pascal is a free Windows-only IDE for Free Pascal and GNU Pascal, with no further development following the 2004 FPC version and the 2005 GPC version.

Bundled libraries

Apart from a compiler and an IDE Free Pascal provides the following libraries:

Examples of software produced with Free Pascal

  • Beyond Compare is a data comparison utility for Windows, OS X, and Linux. The Linux and OS X versions are compiled with Lazarus/FPC.
  • Cartes du Ciel is a free planetarium program for Linux, OS X, and Windows. It maps and labels most constellations, planets, and objects visible by telescope. It was fully written in Lazarus/FPC, and released under GPL.
  • Cheat Engine is an open-source memory scanner, hex editor, and debugger. It can be used for cheating in computer games. Since version 6.0 it is compiled with Lazarus/FPC.
  • D_2D & D_3D data plotting programs.[5]
  • Double Commander is an open-source multi-platform two-panel orthodox file manager inspired by the Microsoft Windows-only Total Commander.
  • Free Pascal is written in Object Pascal and assembly language, and self-compiled.
  • HNSKY, Hallo Northern Sky is a free planetarium program for Windows and Linux. Since version 3.4.0 written & compiled with Lazarus/FPC.
  • Lazarus: Free Pascal’s affiliated Delphi-like software package for rapid development of graphical applications.
  • MeKin2D: package for planar linkage, cam and gear mechanism kinematics.[6]
  • Morfik: Morfik WebOS AppBuilder uses Free Pascal to produce CGI binaries.
  • MyNotex is a free software note-taking and notes manager for GNU/Linux.
  • Peazip is an open source archiver, made with Lazarus/FPC.
  • TorChat, previously written in Python, is now being rewritten in Free Pascal and Lazarus.

See also

  • fpGUI Free Pascal GUI toolkit – a cross-platform and custom-drawn toolkit implemented in Object Pascal

Official websites

General introduction

Sites specialized in game development


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High-level programming language

In computer science, a high-level programming language is a programming language with strong abstraction from the details of the computer. In contrast to low-level programming languages, it may use natural language elements, be easier to use, or may automate (or even hide entirely) significant areas of computing systems (e.g. memory management), making the process of developing a program simpler and more understandable than when using a lower-level language. The amount of abstraction provided defines how “high-level” a programming language is.[1]

In the 1960s, high-level programming languages using a compiler were commonly called autocodes.[2]
Examples of autocodes are COBOL and Fortran.[3]

The first high-level programming language designed for computers was Plankalkül, created by Konrad Zuse.[4] However, it was not implemented in his time, and his original contributions were largely isolated from other developments due to World War II, aside from the language’s influence on the “Superplan” language by Heinz Rutishauser and also to some degree Algol. The first significantly widespread high-level language was Fortran, a machine-independent development of IBM’s earlier Autocode systems. Algol, defined in 1958 and 1960 by committees of European and American computer scientists, introduced recursion as well as nested functions under lexical scope. It was also the first language with a clear distinction between value and name-parameters and their corresponding semantics.[5] Algol also introduced several structured programming concepts, such as the while-do and if-then-else constructs and its syntax was the first to be described in formal notation – “Backus–Naur form” (BNF). During roughly the same period, Cobol introduced records (also called structs) and Lisp introduced a fully general lambda abstraction in a programming language for the first time.

Features

“High-level language” refers to the higher level of abstraction from machine language. Rather than dealing with registers, memory addresses and call stacks, high-level languages deal with variables, arrays, objects, complex arithmetic or boolean expressions, subroutines and functions, loops, threads, locks, and other abstract computer science concepts, with a focus on usability over optimal program efficiency. Unlike low-level assembly languages, high-level languages have few, if any, language elements that translate directly into a machine’s native opcodes. Other features, such as string handling routines, object-oriented language features, and file input/output, may also be present. One thing to note about high-level programming languages is that these languages allow the programmer to be detached and separated from the machine. That is, unlike low-level languages like assembly or machine language, high-level programming can amplify the programmer’s instructions and trigger a lot of data movements in the background without their knowledge. The responsibility and power of executing instructions have been handed over to the machine from the programmer.

Abstraction penalty

High-level languages intend to provide features which standardize common tasks, permit rich debugging, and maintain architectural agnosticism; while low-level languages often produce more efficient code through optimization for a specific system architecture. Abstraction penalty is the cost that high-level programming techniques pay for being unable to optimize performance or use certain hardware because they don’t take advantage of certain low-level architectural resources. High-level programming exhibits features like more generic data structures and operations, run-time interpretation, and intermediate code files; which often result in execution of far more operations than necessary, higher memory consumption, and larger binary program size.[6][7][8] For this reason, code which needs to run particularly quickly and efficiently may require the use of a lower-level language, even if a higher-level language would make the coding easier. In many cases, critical portions of a program mostly in a high-level language can be hand-coded in assembly language, leading to a much faster, more efficient, or simply reliably functioning optimised program.

However, with the growing complexity of modern microprocessor architectures, well-designed compilers for high-level languages frequently produce code comparable in efficiency to what most low-level programmers can produce by hand, and the higher abstraction may allow for more powerful techniques providing better overall results than their low-level counterparts in particular settings.[9]
High-level languages are designed independent of a specific computing system architecture. This facilitates executing a program written in such a language on any computing system with compatible support for the Interpreted or JIT program. High-level languages can be improved as their designers develop improvements. In other cases, new high-level languages evolve from one or more others with the goal of aggregating the most popular constructs with new or improved features. An example of this is Scala which maintains backward compatibility with Java which means that programs and libraries written in Java will continue to be usable even if a programming shop switches to Scala; this makes the transition easier and the lifespan of such high-level coding indefinite. In contrast, low-level programs rarely survive beyond the system architecture which they were written for without major revision. This is the engineering ‘trade-off’ for the ‘Abstraction Penalty’.

Relative meaning

Examples of high-level programming languages in active use today include Python, Visual Basic, Delphi, Perl, PHP, ECMAScript, Ruby, C#, Java and many others.

The terms high-level and low-level are inherently relative. Some decades ago, the C language, and similar languages, were most often considered “high-level”, as it supported concepts such as expression evaluation, parameterised recursive functions, and data types and structures, while assembly language was considered “low-level”. Today, many programmers might refer to C as low-level, as it lacks a large runtime-system (no garbage collection, etc.), basically supports only scalar operations, and provides direct memory addressing. It, therefore, readily blends with assembly language and the machine level of CPUs and microcontrollers.

Assembly language may itself be regarded as a higher level (but often still one-to-one if used without macros) representation of machine code, as it supports concepts such as constants and (limited) expressions, sometimes even variables, procedures, and data structures. Machine code, in its turn, is inherently at a slightly higher level than the microcode or micro-operations used internally in many processors.[10]

Execution modes

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

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

Machine code generation
Some compilers compile source code directly into machine code. This is the original mode of compilation, and languages that are directly and completely transformed to machine-native code in this way may be called truly compiled languages. See assembly language.
Intermediate representations
When code written in a language is compiled to an intermediate representation, that representation can be optimized or saved for later execution without the need to re-read the source file. When the intermediate representation is saved, it may be in a form such as bytecode. The intermediate representation must then be interpreted or further compiled to execute it. Virtual machines that execute bytecode directly or transform it further into machine code have blurred the once clear distinction between intermediate representations and truly compiled languages.
Source-to-source translated or transcompiled
Code written in a language may be translated into terms of a lower-level language for which native code compilers are already common. JavaScript and the language C are common targets for such translators. See CoffeeScript, Chicken Scheme, and Eiffel as examples. Specifically, the generated C and C++ code can be seen (as generated from the Eiffel language when using the EiffelStudio IDE) in the EIFGENs directory of any compiled Eiffel project. In Eiffel, the translated process is referred to as transcompiling or transcompiled, and the Eiffel compiler as a transcompiler or source-to-source compiler.

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

High-level language computer architecture

Alternatively, it is possible for a high-level language to be directly implemented by a computer – the computer directly executes the HLL code. This is known as a high-level language computer architecture – the computer architecture itself is designed to be targeted by a specific high-level language. The Burroughs large systems were target machines for ALGOL 60, for example.[11]


Categories
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BASIC

BASIC (Beginners’ All-purpose Symbolic Instruction Code)[1] is a family of general-purpose, high-level programming languages whose design philosophy emphasizes ease of use. The original version was designed by John G. Kemeny and Thomas E. Kurtz and released at Dartmouth College in 1964. They wanted to enable students in fields other than science and mathematics to use computers. At the time, nearly all use of computers required writing custom software, which was something only scientists and mathematicians tended to learn.

In addition to the language itself, Kemeny and Kurtz developed the Dartmouth Time Sharing System (DTSS), which allowed multiple users to edit and run BASIC programs at the same time. This general model became very popular on minicomputer systems like the PDP-11 and Data General Nova in the late 1960s and early 1970s. Hewlett-Packard produced an entire computer line for this method of operation, introducing the HP2000 series in the late 1960s and continuing sales into the 1980s. Many early video games trace their history to one of these versions of BASIC.

The emergence of early microcomputers in the mid-1970s led to the development of the original Microsoft BASIC in 1975. Due to the tiny main memory available on these machines, often 4 kB, a variety of Tiny BASIC dialects was also created. BASIC was available for almost any system of the era, and naturally became the de facto programming language for the home computer systems that emerged in the late 1970s. These machines almost always had a BASIC installed by default, often in the machine’s firmware or sometimes on a ROM cartridge.

BASIC fell from use during the later 1980s as newer machines with far greater capabilities came to market and other programming languages (such as Pascal and C) became tenable. In 1991, Microsoft released Visual Basic, combining a greatly updated version of BASIC with a visual forms builder. This reignited use of the language and “VB” remains a major programming language in the form of VB.NET.

Origin

John G. Kemeny was the math department chairman at Dartmouth College. Based largely on his reputation as an innovator in math teaching, in 1959 the school won an Alfred P. Sloan Foundation award for $500,000 to build a new department building.[2]Thomas E. Kurtz had joined the department in 1956, and from the 1960s Kemeny and Kurtz agreed on the need for programming literacy among students outside the traditional STEM fields. Kemeny later noted that “Our vision was that every student on campus should have access to a computer, and any faculty member should be able to use a computer in the classroom whenever appropriate. It was as simple as that.”[3]

Kemeny and Kurtz had made two previous experiments with simplified languages, DARSIMCO (Dartmouth Simplified Code) and DOPE (Dartmouth Oversimplified Programming Experiment). These did not progress past a single freshman class. New experiments using Fortran and ALGOL followed, but Kurtz concluded these languages were too tricky for what they desired. As Kurtz noted, Fortran had numerous oddly-formed commands, notably an “almost impossible-to-memorize convention for specifying a loop: ‘DO 100, I = 1, 10, 2’. Is it ‘1, 10, 2’ or ‘1, 2, 10’, and is the comma after the line number required or not?”[3]

Moreover, the lack of any sort of immediate feedback was a key problem; the machines of the era used batch processing and took a long time to complete a run of a program. Kurtz suggested that time-sharing offered a solution; a single machine could divide up its processing time among many users, giving them the illusion of having a slow computer to themselves. Small programs would return results in a few seconds. This led to increasing interest in a system using time-sharing and a new language specifically for use by non-STEM students.[3]

Kemeny wrote the first version of BASIC. The acronym BASIC comes from the name of an unpublished paper by Thomas Kurtz.[4] The new language was heavily patterned on FORTRAN II; statements were one-to-a-line, numbers were used to indicate the target of loops and branches, and many of the commands were similar or identical. However, the syntax was changed wherever it could be improved. For instance, the difficult to remember DO loop was replaced by the much easier to remember FOR I = 1 TO 10 STEP 2, and the line number used in the DO was instead indicated by the NEXT I.[a] Likewise, the cryptic IF statement of Fortran, whose syntax matched a particular instruction of the machine on which it was originally written, became the simpler IF I=5 THEN GOTO 100. These changes made the language much less idiosyncratic while still having an overall structure and feel similar to the original FORTRAN.[3]

The project received a $300,000 grant from the National Science Foundation, which was used to purchase a GE-225 computer for processing, and a Datanet-30 realtime processor to handle the Teletype Model 33 teleprinters used for input and output. A team of a dozen undergraduates worked on the project for about a year, writing both the DTSS system and the BASIC compiler.[3] The main CPU was later replaced by a GE-235,[3] and still later by a GE-635.

The first version BASIC language was released on 1 May 1964.[5][6]

One of the graduate students on the implementation team was Mary Kenneth Keller, one of the first people in the United States to earn a Ph.D. in computer science and the first woman to do so.[7]

Initially, BASIC concentrated on supporting straightforward mathematical work, with matrix arithmetic support from its initial implementation as a batch language, and character string functionality being added by 1965.
Wanting use of the language to become widespread, its designers made the compiler available free of charge. (In the 1960s, software became a chargeable commodity; until then, it was provided without charge as a service with the very expensive computers, usually available only to lease.) They also made it available to high schools in the Hanover, New Hampshire area and put considerable effort into promoting the language. In the following years, as other dialects of BASIC appeared, Kemeny and Kurtz’s original BASIC dialect became known as Dartmouth BASIC.

New Hampshire recognized the accomplishment in 2019 when it erected a highway historical marker recognizing the creation of BASIC.[8]

Spread on minicomputers

“Train Basic every day!”—reads a poster (bottom center) in a Russian school (c. 1985–1986).

Knowledge of the relatively simple BASIC became widespread for a computer language, and it was implemented by a number of manufacturers, becoming fairly popular on newer minicomputers, such as the DEC PDP series, where BASIC-PLUS was an extended dialect for use on the RSTS/E time-sharing operating system. The BASIC language was available for the Data General Nova, and also central to the HP Time-Shared BASIC system in the late 1960s and early 1970s, where the language was implemented as an interpreter. A version was a core part of the Pick operating system from 1973 onward, where a compiler renders it into bytecode, able to be interpreted by a virtual machine.

During this period a number of simple text-based games were written in BASIC, most notably Mike Mayfield’s Star Trek. A number of these were collected by DEC employee David H. Ahl and published in a newsletter he compiled. He later collected a number of these into book form, 101 BASIC Computer Games, published in 1973.[9] During the same period, Ahl was involved in the creation of a small computer for education use, an early personal computer. When management refused to support the concept, Ahl left DEC in 1974 to found the seminal computer magazine, Creative Computing. The book remained popular, and was re-published on several occasions.[10]

Explosive growth: the home computer era

MSX BASIC version 3.0

The introduction of the first microcomputers in the mid-1970s was the start of explosive growth for BASIC. It had the advantage that it was fairly well known to the young designers and computer hobbyists who took an interest in microcomputers. Despite Dijkstra‘s famous judgement in 1975, “It is practically impossible to teach good programming to students that have had a prior exposure to BASIC: as potential programmers they are mentally mutilated beyond hope of regeneration”,[11] BASIC was one of the few languages that was both high-level enough to be usable by those without training and small enough to fit into the microcomputers of the day, making it the de facto standard programming language on early microcomputers.

The first microcomputer version of BASIC was co-written by Gates, Allen, and Monte Davidoff for their newly-formed company, Micro-Soft. This was released by MITS in punch tape format for the Altair 8800 shortly after the machine itself,[12] immediately cementing BASIC as the primary language of early microcomputers. Members of the Homebrew Computer Club began circulating copies of the program, causing Gates to write his Open Letter to Hobbyists, complaining about this early example of software piracy.

Partially in response, Bob Albrecht urged Dennis Allison to write their own variation of the language. Albrecht had seen BASIC on minicomputers and felt it would be the perfect match for new machines. How to design and implement a stripped-down version of an interpreter for the BASIC language was covered in articles by Allison in the first three quarterly issues of the People’s Computer Company newsletter published in 1975 and implementations with source code published in Dr. Dobb’s Journal of Tiny BASIC Calisthenics & Orthodontia: Running Light Without Overbyte. This led to a wide variety of versions with added features or other improvements, with versions from Tom Pittman and Li-Chen Wang becoming particularly well known.[13]

Micro-Soft, by this time Microsoft, ported their interpreter for the MOS 6502, which quickly become one of the most popular microprocessors of the 8-bit era. When new microcomputers began to appear, notably the “1977 trinity” of the TRS-80, Commodore PET and Apple II, they either included a version of the MS code, or quickly introduced new models with it. By 1978, MS BASIC was a de facto standard and practically every home computer of the 1980s included it in ROM. Upon boot, a BASIC interpreter in direct mode was presented.

Commodore Business Machines included Commodore BASIC, based on Microsoft BASIC. The Apple II and TRS-80 each had two versions of BASIC, a smaller introductory version introduced with the initial releases of the machines and a more advanced version developed as interest in the platforms increased. As new companies entered the field, additional versions were added that subtly changed the BASIC family. The Atari 8-bit family had its own Atari BASIC that was modified in order to fit on an 8 kB ROM cartridge. Sinclair BASIC was introduced in 1980 with the Sinclair ZX-80, and was later extended for the Sinclair ZX-81 and the Sinclair ZX Spectrum. The BBC published BBC BASIC, developed by Acorn Computers Ltd, incorporating many extra structured programming keywords and advanced floating-point operation features.

As the popularity of BASIC grew in this period, computer magazines published complete source code in BASIC for video games, utilities, and other programs. Given BASIC’s straightforward nature, it was a simple matter to type in the code from the magazine and execute the program. Different magazines were published featuring programs for specific computers, though some BASIC programs were considered universal and could be used in machines running any variant of BASIC (sometimes with minor adaptations). Many books of type-in programs were also available, and in particular, Ahl published versions of the original 101 BASIC games converted into the Microsoft dialect and published it from Creative Computing as BASIC Computer Games. This book, and its sequels, provided hundreds of ready-to-go programs that could be easily converted to practically any BASIC-running platform.[9][14][15] The book reached the stores in 1978, just as the home computer market was starting off, and it became the first million-selling computer book. Later packages, such as Learn to Program BASIC would also have gaming as an introductory focus. On the business-focused CP/M computers which soon became widespread in small business environments, Microsoft BASIC (MBASIC) was one of the leading applications.[16]

IBM PC and compatibles

When IBM was designing the IBM PC they followed the paradigm of existing home computers in wanting to have a built-in BASIC. They sourced this from Microsoft – IBM Cassette BASIC – but Microsoft also produced several other versions of BASIC for MS-DOS/PC DOS including IBM Disk BASIC (BASIC D), IBM BASICA (BASIC A), GW-BASIC (a BASICA-compatible version that did not need IBM’s ROM) and QBasic, all typically bundled with the machine. In addition they produced the Microsoft BASIC Compiler aimed at professional programmers. Turbo Pascal-publisher Borland published Turbo Basic 1.0 in 1985 (successor versions are still being marketed by the original author under the name PowerBASIC). Microsoft wrote the windowed AmigaBASIC that was supplied with version 1.1 of the pre-emptive multitasking GUI Amiga computers (late 1985 / early 1986), although the product unusually did not bear any Microsoft marks.

These later variations introduced many extensions, such as improved string manipulation and graphics support, access to the file system and additional data types. More important were the facilities for structured programming, including additional control structures and proper subroutines supporting local variables. However, by the latter half of the 1980s, users were increasingly using pre-made applications written by others rather than learning programming themselves; while professional programmers now had a wide range of more advanced languages available on small computers. C and later C++ became the languages of choice for professional “shrink wrap” application development.[17][18]

Visual Basic

In 1991 Microsoft introduced Visual Basic, an evolutionary development of QuickBasic. It included constructs from that language such as block-structured control statements, parameterized subroutines, and optional static typing, as well as object-oriented constructs from other languages such as “With” and “For Each”. The language retained some compatibility with its predecessors, such as the Dim keyword for declarations, “Gosub”/Return statements, and optional line numbers which could be used to locate errors. An important driver for the development of Visual Basic was as the new macro language for Microsoft Excel, a spreadsheet program. To the surprise of many at Microsoft who still initially marketed it as a language for hobbyists, the language came into widespread use for small custom business applications shortly after the release of VB version 3.0, which is widely considered the first relatively stable version.

While many advanced programmers still scoffed at its use, VB met the needs of small businesses efficiently as by that time, computers running Windows 3.1 had become fast enough that many business-related processes could be completed “in the blink of an eye” even using a “slow” language, as long as large amounts of data were not involved. Many small business owners found they could create their own small, yet useful applications in a few evenings to meet their own specialized needs. Eventually, during the lengthy lifetime of VB3, knowledge of Visual Basic had become a marketable job skill. Microsoft also produced VBScript in 1996 and Visual Basic .NET in 2001. The latter has essentially the same power as C# and Java but with syntax that reflects the original Basic language.

Three modern Basic variants: Mono Basic, OpenOffice.org Basic and Gambas

Post-1990 versions and dialects

Many other BASIC dialects have also sprung up since 1990, including the open source QB64 and FreeBASIC, inspired by QBasic, and the Visual Basic-styled RapidQ, Basic For Qt and Gambas. Modern commercial incarnations include PureBasic, PowerBASIC, Xojo, Monkey X and True BASIC (the direct successor to Dartmouth BASIC from a company controlled by Kurtz).

Several web-based simple BASIC interpreters also now exist, including Quite BASIC and Microsoft’s Small Basic. Many versions of BASIC are also now available for smartphones and tablets via the Apple App Store, or Google Play store for Android. On game consoles, an application for the Nintendo 3DS and Nintendo DSi called Petit Computer allows for programming in a slightly modified version of BASIC with DS button support.

Calculators

Variants of BASIC are available on graphing and otherwise programmable calculators made by Texas Instruments, HP, Casio, and others.

Windows command line

QBasic, a version of Microsoft QuickBASIC without the linker to make EXE files, is present in the Windows NT and DOS-Windows 95 streams of operating systems and can be obtained for more recent releases like Windows 7 which do not have them. Prior to DOS 5, the Basic interpreter was GW-Basic. QuickBasic is part of a series of three languages issued by Microsoft for the home and office power user and small-scale professional development; QuickC and QuickPascal are the other two. For Windows 95 and 98, which do not have QBasic installed by default, they can be copied from the installation disc, which will have a set of directories for old and optional software; other missing commands like Exe2Bin and others are in these same directories.

Other

BASIC came to some video game systems, such as the Nintendo Famicom.

The various Microsoft, Lotus, and Corel office suites and related products are programmable with Visual Basic in one form or another, including LotusScript, which is very similar to VBA 6. The Host Explorer terminal emulator uses WWB as a macro language; or more recently the programme and the suite in which it is contained is programmable in an in-house Basic variant known as Hummingbird Basic. The VBScript variant is used for programming web content, Outlook 97, Internet Explorer, and the Windows Script Host. WSH also has a Visual Basic for Applications (VBA) engine installed as the third of the default engines along with VBScript, JScript, and the numerous proprietary or open source engines which can be installed like PerlScript, a couple of Rexx-based engines, Python, Ruby, Tcl, Delphi, XLNT, PHP, and others; meaning that the two versions of Basic can be used along with the other mentioned languages, as well as LotusScript, in a WSF file, through the component object model, and other WSH and VBA constructions. VBScript is one of the languages that can be accessed by the 4Dos, 4NT, and Take Command enhanced shells. SaxBasic and WWB are also very similar to the Visual Basic line of Basic implementations. The pre-Office 97 macro language for Microsoft Word is known as WordBASIC. Excel 4 and 5 use Visual Basic itself as a macro language. Chipmunk Basic, an old school interpreter similar to BASICs of the 1970s, is available for Linux, Microsoft Windows and macOS.

Nostalgia

The ubiquity of BASIC interpreters on personal computers was such that textbooks once included simple “Try It In BASIC” exercises that encouraged students to experiment with mathematical and computational concepts on classroom or home computers. Popular computer magazines of the day typically included type-in programs.

Futurist and sci-fi writer David Brin mourned the loss of ubiquitous BASIC in a 2006 Salon article[19] as have others who first used computers during this era. In turn, the article prompted Microsoft to develop and release Small Basic.[20] Dartmouth held a 50th anniversary celebration for BASIC on 1 May 2014,[21] as did other organisations; at least one organisation of VBA programmers organised a 35th anniversary observance in 1999.[22]

Dartmouth College celebrated the 50th anniversary of the BASIC language with a day of events[23] on April 30, 2014. A short documentary film was produced for the event.[24]

Syntax

Typical BASIC keywords

Data manipulation

LET 
assigns a value (which may be the result of an expression) to a variable.
DATA 
holds a list of values which are assigned sequentially using the READ command.

Program flow control

IF ... THEN ... {ELSE} 
used to perform comparisons or make decisions.
FOR ... TO ... {STEP} ... NEXT 
repeat a section of code a given number of times. A variable that acts as a counter is available within the loop.
WHILE ... WEND and REPEAT ... UNTIL 
repeat a section of code while the specified condition is true. The condition may be evaluated before each iteration of the loop, or after.
DO ... LOOP {WHILE} or {UNTIL} 
repeat a section of code indefinitely or while/until the specified condition is true. The condition may be evaluated before each iteration of the loop, or after.
GOTO 
jumps to a numbered or labelled line in the program.
GOSUB 
jumps to a numbered or labelled line, executes the code it finds there until it reaches a RETURN command, on which it jumps back to the statement following the GOSUB, either after a colon, or on the next line. This is used to implement subroutines.
ON ... GOTO/GOSUB 
chooses where to jump based on the specified conditions. See Switch statement for other forms.
DEF FN 
a pair of keywords introduced in the early 1960s to define functions. The original BASIC functions were modelled on FORTRAN single-line functions. BASIC functions were one expression with variable arguments, rather than subroutines, with a syntax on the model of DEF FND(x) = x*x at the beginning of a program. Function names were originally restricted to FN, plus one letter, i.e., FNA, FNB …

Input and output

LIST 
displays the full source code of the current program.
PRINT 
displays a message on the screen or other output device.
INPUT 
asks the user to enter the value of a variable. The statement may include a prompt message.
TAB or AT
used with PRINT to set the position where the next character will be shown on the screen or printed on paper.

Mathematical functions

ABS 
Absolute value
ATN 
Arctangent (result in radians)
COS 
Cosine (argument in radians)
EXP 
Exponential function
INT 
Integer part (typically floor function)
LOG 
Natural logarithm
RND 
Random number generation
SIN 
Sine (argument in radians)
SQR 
Square root
TAN 
Tangent (argument in radians)

Miscellaneous

REM 
holds a programmer’s comment or REMark; often used to give a title to the program and to help identify the purpose of a given section of code.
USR 
transfers program control to a machine language subroutine, usually entered as an alphanumeric string or in a list of DATA statements.
TRON 
turns on display of each line number as it is run (“TRace ON”). This was useful for debugging or correcting of problems in a program.
TROFF 
turns off the display of line numbers.
ASM 
some compilers such as Freebasic,[25] Purebasic,[26] and Powerbasic[27] also support inline assembly language, allowing the programmer to intermix high-level and low-level code, typically prefixed with “ASM” or “!” statements.

Data types and variables

Minimal versions of BASIC had only integer variables and one- or two-letter variable names, which minimized requirements of limited and expensive memory (RAM). More powerful versions had floating-point arithmetic, and variables could be labelled with names six or more characters long. There were some problems and restrictions in early implementations; for example, Applesoft allowed variable names to be several characters long, but only the first two were significant, thus it was possible to inadvertently write a program with variables “LOSS” and “LOAN”, which would be treated as being the same; assigning a value to “LOAN” would silently overwrite the value intended as “LOSS”. Keywords could not be used in variables in many early BASICs; “SCORE” would be interpreted as “SC” OR “E”, where OR was a keyword. String variables are usually distinguished in many microcomputer dialects by having $ suffixed to their name, and values are often identified as strings by being delimited by “double quotation marks”. Arrays in BASIC could contain integers, floating point or string variables.

Some dialects of BASIC supported matrices and matrix operations, useful for the solution of sets of simultaneous linear algebraic equations. These dialects would directly support matrix operations such as assignment, addition, multiplication (of compatible matrix types), and evaluation of a determinant. Many microcomputer BASICs did not support this data type; matrix operations were still possible, but had to be programmed explicitly on array elements.

Examples

Unstructured BASIC

The original Dartmouth Basic was unusual in having a matrix keyword, MAT.[b] Although not implemented by most later microprocessor derivatives, it is used in this example from the 1968 manual[28] which averages the numbers that are input:

5 LET S = 0
10 MAT INPUT V 
20 LET N = NUM 
30 IF N = 0 THEN 99 
40 FOR I = 1 TO N 
45 LET S = S + V(I) 
50 NEXT I 
60 PRINT S/N 
70 GO TO 5 
99 END

New BASIC programmers on a home computer might start with a simple program, perhaps using the language’s PRINT statement to display a message on the screen; a well-known and often-replicated example is Kernighan and Ritchie‘s “Hello, World!” program:

10 PRINT "Hello, World!"
20 END

An infinite loop could be used to fill the display with the message.

Most first-generation BASIC versions, such as MSX BASIC and GW-BASIC, supported simple data types, loop cycles, and arrays. The following example is written for GW-BASIC, but will work in most versions of BASIC with minimal changes:

10 INPUT "What is your name: "; U$
20 PRINT "Hello "; U$
30 INPUT "How many stars do you want: "; N
40 S$ = ""
50 FOR I = 1 TO N
60 S$ = S$ + "*"
70 NEXT I
80 PRINT S$
90 INPUT "Do you want more stars? "; A$
100 IF LEN(A$) = 0 THEN GOTO 90
110 A$ = LEFT$(A$, 1)
120 IF A$ = "Y" OR A$ = "y" THEN GOTO 30
130 PRINT "Goodbye "; U$
140 END

The resulting dialog might resemble:

What is your name: Mike
Hello Mike
How many stars do you want: 7
*******
Do you want more stars? yes
How many stars do you want: 3
***
Do you want more stars? no
Goodbye Mike

Structured BASIC

Second-generation BASICs (for example, VAX Basic, SuperBASIC, True BASIC, QuickBASIC, BBC BASIC, Pick BASIC, PowerBASIC and (arguably) COMAL introduced a number of features into the language, primarily related to structured and procedure-oriented programming. Usually, line numbering is omitted from the language and replaced with labels (for GOTO) and procedures to encourage easier and more flexible design.[29] In addition keywords and structures to support repetition, selection and procedures with local variables were introduced.

The following example is in Microsoft QuickBASIC:

REM QuickBASIC example

REM Forward declaration - allows the main code to call a
REM    subroutine that is declared later in the source code
DECLARE SUB PrintSomeStars (StarCount!)

REM Main program follows
INPUT "What is your name: ", UserName$
PRINT "Hello "; UserName$
DO
   INPUT "How many stars do you want: ", NumStars
   CALL PrintSomeStars(NumStars)
   DO
      INPUT "Do you want more stars? ", Answer$
   LOOP UNTIL Answer$ <> ""
   Answer$ = LEFT$(Answer$, 1)
LOOP WHILE UCASE$(Answer$) = "Y"
PRINT "Goodbye "; UserName$
END

REM subroutine declaration
SUB PrintSomeStars (StarCount)
   REM This procedure uses a local variable called Stars$
   Stars$ = STRING$(StarCount, "*")
   PRINT Stars$
END SUB

Object-oriented BASIC

Third-generation BASIC dialects such as Visual Basic, Xojo, StarOffice Basic and BlitzMax introduced features to support object-oriented and event-driven programming paradigm. Most built-in procedures and functions are now represented as methods of standard objects rather than operators. Also, the operating system became increasingly accessible to the BASIC language.

The following example is in Visual Basic .NET:

Public Module StarsProgram
   Private Function Ask(prompt As String) As String
      Console.Write(prompt)
      Return Console.ReadLine()
   End Function

   Public Sub Main()
      Dim userName = Ask("What is your name: ")
      Console.WriteLine("Hello {0}", userName)

      Dim answer As String

      Do
         Dim numStars = CInt(Ask("How many stars do you want: "))
         Dim stars As New String("*"c, numStars)
         Console.WriteLine(stars)

         Do
            answer = Ask("Do you want more stars? ")
         Loop Until answer <> ""
      Loop While answer.StartsWith("Y", StringComparison.OrdinalIgnoreCase)

      Console.WriteLine("Goodbye {0}", userName)
   End Sub
End Module

Standards

  • ANSI/ISO/IEC Standard for Minimal BASIC:
    • ANSI X3.60-1978 “For minimal BASIC”
    • ISO/IEC 6373:1984 “Data Processing—Programming Languages—Minimal BASIC”
  • ECMA-55 Minimal BASIC (withdrawn, similar to ANSI X3.60-1978)
  • ANSI/ISO/IEC Standard for Full BASIC:
    • ANSI X3.113-1987 “Programming Languages Full BASIC”
    • INCITS/ISO/IEC 10279-1991 (R2005) “Information Technology – Programming Languages – Full BASIC”
  • ANSI/ISO/IEC Addendum Defining Modules:
    • ANSI X3.113 Interpretations-1992 “BASIC Technical Information Bulletin # 1 Interpretations of ANSI 03.113-1987”
    • ISO/IEC 10279:1991/ Amd 1:1994 “Modules and Single Character Input Enhancement”
  • ECMA-116 BASIC (withdrawn, similar to ANSI X3.113-1987)

Notes

General references


Categories
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English language

English is a West Germanic language that was first spoken in early medieval England and eventually became a global lingua franca.[4][5] It is named after the Angles, one of the Germanic tribes that migrated to the area of Great Britain that later took their name, as England. Both names derive from Anglia, a peninsula in the Baltic Sea. The language is closely related to Frisian and Low Saxon, and its vocabulary has been significantly influenced by other Germanic languages, particularly Norse (a North Germanic language), and to a greater extent by Latin and French.[6]

English has developed over the course of more than 1,400 years. The earliest forms of English, a group of West Germanic (Ingvaeonic) dialects brought to Great Britain by Anglo-Saxon settlers in the 5th century, are collectively called Old English. Middle English began in the late 11th century with the Norman conquest of England; this was a period in which the language was influenced by French.[7]Early Modern English began in the late 15th century with the introduction of the printing press to London, the printing of the King James Bible and the start of the Great Vowel Shift.[8]

Modern English has been spreading around the world since the 17th century by the worldwide influence of the British Empire and the United States. Through all types of printed and electronic media of these countries, English has become the leading language of international discourse and the lingua franca in many regions and professional contexts such as science, navigation and law.[9]

English is the largest language by number of speakers,[10] and the third most-spoken native language in the world, after Standard Chinese and Spanish.[11] It is the most widely learned second language and is either the official language or one of the official languages in almost 60 sovereign states. There are more people who have learned it as a second language than there are native speakers. It is estimated that there are over 2 billion speakers of English.[12] English is the majority native language in the United States, the United Kingdom, Canada, Australia, New Zealand and the Republic of Ireland, and it is widely spoken in some areas of the Caribbean, Africa and South Asia.[13] It is a co-official language of the United Nations, the European Union and many other world and regional international organisations. It is the most widely spoken Germanic language, accounting for at least 70% of speakers of this Indo-European branch. English has a vast vocabulary, though counting how many words any language has is impossible.[14][15] English speakers are called “Anglophones”.

Modern English grammar is the result of a gradual change from a typical Indo-European dependent marking pattern, with a rich inflectional morphology and relatively free word order, to a mostly analytic pattern with little inflection, a fairly fixed SVO word order and a complex syntax.[16]Modern English relies more on auxiliary verbs and word order for the expression of complex tenses, aspect and mood, as well as passive constructions, interrogatives and some negation. The variation among the accents and dialects of English used in different countries and regions—in terms of phonetics and phonology, and sometimes also vocabulary, grammar, and spelling—can often be understood by speakers of different dialects, but in extreme cases can lead to confusion or even mutual unintelligibility between English speakers.

Classification

Anglic languages

  English
  Scots

Anglo-Frisian languages
Anglic and

North Sea Germanic languages Anglo-Frisian and

West Germanic languages
North Sea Germanic and

  Dutch; in Africa: Afrikaans

…… German (High):

  Upper

…… Yiddish

English is an Indo-European language and belongs to the West Germanic group of the Germanic languages.[17]Old English originated from a Germanic tribal and linguistic continuum along the Frisian North Sea coast, whose languages gradually evolved into the Anglic languages in the British Isles, and into the Frisian languages and Low German/Low Saxon on the continent. The Frisian languages, which together with the Anglic languages form the Anglo-Frisian languages, are the closest living relatives of English. Low German/Low Saxon is also closely related, and sometimes English, the Frisian languages, and Low German are grouped together as the Ingvaeonic (North Sea Germanic) languages, though this grouping remains debated.[18] Old English evolved into Middle English, which in turn evolved into Modern English.[19] Particular dialects of Old and Middle English also developed into a number of other Anglic languages, including Scots[20] and the extinct Fingallian and Forth and Bargy (Yola) dialects of Ireland.[21]

Like Icelandic and Faroese, the development of English in the British Isles isolated it from the continental Germanic languages and influences. It has since evolved considerably. English is not mutually intelligible with any continental Germanic language, differing in vocabulary, syntax, and phonology, although some of these, such as Dutch or Frisian, do show strong affinities with English, especially with its earlier stages.[22]

Unlike Icelandic and Faroese, which were isolated, the development of English was influenced by a long series of invasions of the British Isles by other peoples and languages, particularly Old Norse and Norman French. These left a profound mark of their own on the language, so that English shows some similarities in vocabulary and grammar with many languages outside its linguistic clades—but it is not mutually intelligible with any of those languages either. Some scholars have argued that English can be considered a mixed language or a creole—a theory called the Middle English creole hypothesis. Although the great influence of these languages on the vocabulary and grammar of Modern English is widely acknowledged, most specialists in language contact do not consider English to be a true mixed language.[23][24]

English is classified as a Germanic language because it shares innovations with other Germanic languages such as Dutch, German, and Swedish.[25] These shared innovations show that the languages have descended from a single common ancestor called Proto-Germanic. Some shared features of Germanic languages include the division of verbs into strong and weak classes, the use of modal verbs, and the sound changes affecting Proto-Indo-European consonants, known as Grimm’s and Verner’s laws. English is classified as an Anglo-Frisian language because Frisian and English share other features, such as the palatalisation of consonants that were velar consonants in Proto-Germanic (see Phonological history of Old English § Palatalization).[26]

History

Proto-Germanic to Old English

The opening to the Old English epic poem Beowulf, handwritten in half-uncial script:
Hƿæt ƿē Gārde/na ingēar dagum þēod cyninga / þrym ge frunon…
“Listen! We of the Spear-Danes from days of yore have heard of the glory of the folk-kings…”

The earliest form of English is called Old English or Anglo-Saxon (c. 550–1066 CE). Old English developed from a set of North Sea Germanic dialects originally spoken along the coasts of Frisia, Lower Saxony, Jutland, and Southern Sweden by Germanic tribes known as the Angles, Saxons, and Jutes. From the 5th century CE, the Anglo-Saxons settled Britain as the Roman economy and administration collapsed. By the 7th century, the Germanic language of the Anglo-Saxons became dominant in Britain, replacing the languages of Roman Britain (43–409 CE): Common Brittonic, a Celtic language, and Latin, brought to Britain by the Roman occupation.[27][28][29]England and English (originally Ænglaland and Ænglisc) are named after the Angles.[30]

Old English was divided into four dialects: the Anglian dialects (Mercian and Northumbrian) and the Saxon dialects, Kentish and West Saxon.[31] Through the educational reforms of King Alfred in the 9th century and the influence of the kingdom of Wessex, the West Saxon dialect became the standard written variety.[32] The epic poem Beowulf is written in West Saxon, and the earliest English poem, Cædmon’s Hymn, is written in Northumbrian.[33] Modern English developed mainly from Mercian, but the Scots language developed from Northumbrian. A few short inscriptions from the early period of Old English were written using a runic script.[34] By the 6th century, a Latin alphabet was adopted, written with half-uncial letterforms. It included the runic letters wynnƿ⟩ and thornþ⟩, and the modified Latin letters ethð⟩, and ashæ⟩.[34][35]

Old English is very different from Modern English, and is difficult for 21st-century English speakers to understand. Its grammar was similar to that of modern German, and its closest relative is Old Frisian. Nouns, adjectives, pronouns, and verbs had many more inflectional endings and forms, and word order was much freer than in Modern English. Modern English has case forms in pronouns (he, him, his) and has a few verb inflections (speak, speaks, speaking, spoke, spoken), but Old English had case endings in nouns as well, and verbs had more person and number endings.[36][37][38]

The translation of Matthew 8:20 from 1000 CE shows examples of case endings (nominative plural, accusative plural, genitive singular) and a verb ending (present plural):

Foxas habbað holu and heofonan fuglas nest
Fox-as habb-að hol-u and heofon-an fugl-as nest-∅
fox-NOM.PL have-PRS.PL hole-ACC.PL and heaven-GEN.SG bird-NOM.PL nest-ACC.PL
“Foxes have holes and the birds of heaven nests”[39]

Middle English

Englischmen þeyz hy hadde fram þe bygynnyng þre manner speche, Souþeron, Northeron, and Myddel speche in þe myddel of þe lond, … Noþeles by comyxstion and mellyng, furst wiþ Danes, and afterward wiþ Normans, in menye þe contray longage ys asperyed, and som vseþ strange wlaffyng, chyteryng, harryng, and garryng grisbytting.

Although, from the beginning, Englishmen had three manners of speaking, southern, northern and midlands speech in the middle of the country, … Nevertheless, through intermingling and mixing, first with Danes and then with Normans, amongst many the country language has arisen, and some use strange stammering, chattering, snarling, and grating gnashing.

John of Trevisa, ca. 1385[40]

From the 8th to the 12th century, Old English gradually transformed through language contact into Middle English. Middle English is often arbitrarily defined as beginning with the conquest of England by William the Conqueror in 1066, but it developed further in the period from 1200–1450.

First, the waves of Norse colonisation of northern parts of the British Isles in the 8th and 9th centuries put Old English into intense contact with Old Norse, a North Germanic language. Norse influence was strongest in the north-eastern varieties of Old English spoken in the Danelaw area around York, which was the centre of Norse colonisation; today these features are still particularly present in Scots and Northern English. However the centre of norsified English seems to have been in the Midlands around Lindsey, and after 920 CE when Lindsey was reincorporated into the Anglo-Saxon polity, Norse features spread from there into English varieties that had not been in direct contact with Norse speakers. An element of Norse influence that persists in all English varieties today is the group of pronouns beginning with th- (they, them, their) which replaced the Anglo-Saxon pronouns with h- (hie, him, hera).[41]

With the Norman conquest of England in 1066, the now norsified Old English language was subject to contact with the Old Norman language, a Romance language closely related to Modern French. The Norman language in England eventually developed into Anglo-Norman. Because Norman was spoken primarily by the elites and nobles, while the lower classes continued speaking Anglo-Saxon, the main influence of Norman was the introduction of a wide range of loanwords related to politics, legislation and prestigious social domains.[42] Middle English also greatly simplified the inflectional system, probably in order to reconcile Old Norse and Old English, which were inflectionally different but morphologically similar. The distinction between nominative and accusative cases was lost except in personal pronouns, the instrumental case was dropped, and the use of the genitive case was limited to indicating possession. The inflectional system regularised many irregular inflectional forms,[43] and gradually simplified the system of agreement, making word order less flexible.[44] In the Wycliffe Bible of the 1380s, the verse Matthew 8:20 was written:

Foxis han dennes, and briddis of heuene han nestis[45]

Here the plural suffix -n on the verb have is still retained, but none of the case endings on the nouns are present. By the 12th century Middle English was fully developed, integrating both Norse and Norman features; it continued to be spoken until the transition to early Modern English around 1500. Middle English literature includes Geoffrey Chaucer‘s The Canterbury Tales, and Malory’s Le Morte d’Arthur. In the Middle English period, the use of regional dialects in writing proliferated, and dialect traits were even used for effect by authors such as Chaucer.[46]

Early Modern English

Graphic representation of the Great Vowel Shift, showing how the pronunciation of the long vowels gradually shifted, with the high vowels i: and u: breaking into diphthongs and the lower vowels each shifting their pronunciation up one level

The next period in the history of English was Early Modern English (1500–1700). Early Modern English was characterised by the Great Vowel Shift (1350–1700), inflectional simplification, and linguistic standardisation.

The Great Vowel Shift affected the stressed long vowels of Middle English. It was a chain shift, meaning that each shift triggered a subsequent shift in the vowel system. Mid and open vowels were raised, and close vowels were broken into diphthongs. For example, the word bite was originally pronounced as the word beet is today, and the second vowel in the word about was pronounced as the word boot is today. The Great Vowel Shift explains many irregularities in spelling since English retains many spellings from Middle English, and it also explains why English vowel letters have very different pronunciations from the same letters in other languages.[47][48]

English began to rise in prestige, relative to Norman French, during the reign of Henry V. Around 1430, the Court of Chancery in Westminster began using English in its official documents, and a new standard form of Middle English, known as Chancery Standard, developed from the dialects of London and the East Midlands. In 1476, William Caxton introduced the printing press to England and began publishing the first printed books in London, expanding the influence of this form of English.[49] Literature from the Early Modern period includes the works of William Shakespeare and the translation of the Bible commissioned by King James I. Even after the vowel shift the language still sounded different from Modern English: for example, the consonant clusters /kn ɡn sw/ in knight, gnat, and sword were still pronounced. Many of the grammatical features that a modern reader of Shakespeare might find quaint or archaic represent the distinct characteristics of Early Modern English.[50]

In the 1611 King James Version of the Bible, written in Early Modern English, Matthew 8:20 says:

The Foxes haue holes and the birds of the ayre haue nests[39]

This exemplifies the loss of case and its effects on sentence structure (replacement with Subject-Verb-Object word order, and the use of of instead of the non-possessive genitive), and the introduction of loanwords from French (ayre) and word replacements (bird originally meaning “nestling” had replaced OE fugol).[51]

Spread of Modern English

By the late 18th century, the British Empire had spread English through its colonies and geopolitical dominance. Commerce, science and technology, diplomacy, art, and formal education all contributed to English becoming the first truly global language. English also facilitated worldwide international communication.[52][9] England continued to form new colonies, and these later developed their own norms for speech and writing. English was adopted in parts of North America, parts of Africa, Australasia, and many other regions. When they obtained political independence, some of the newly independent nations that had multiple indigenous languages opted to continue using English as the official language to avoid the political and other difficulties inherent in promoting any one indigenous language above the others.[53][54][55] In the 20th century the growing economic and cultural influence of the United States and its status as a superpower following the Second World War has, along with worldwide broadcasting in English by the BBC[56] and other broadcasters, caused the language to spread across the planet much faster.[57][58] In the 21st century, English is more widely spoken and written than any language has ever been.[59]

As Modern English developed, explicit norms for standard usage were published, and spread through official media such as public education and state-sponsored publications. In 1755 Samuel Johnson published his A Dictionary of the English Language which introduced standard spellings of words and usage norms. In 1828, Noah Webster published the American Dictionary of the English language to try to establish a norm for speaking and writing American English that was independent of the British standard. Within Britain, non-standard or lower class dialect features were increasingly stigmatised, leading to the quick spread of the prestige varieties among the middle classes.[60]

In modern English, the loss of grammatical case is almost complete (it is now only found in pronouns, such as he and him, she and her, who and whom), and SVO word-order is mostly fixed.[60] Some changes, such as the use of do-support have become universalised. (Earlier English did not use the word “do” as a general auxiliary as Modern English does; at first it was only used in question constructions, and even then was not obligatory.[61] Now, do-support with the verb have is becoming increasingly standardised.) The use of progressive forms in -ing, appears to be spreading to new constructions, and forms such as had been being built are becoming more common. Regularisation of irregular forms also slowly continues (e.g. dreamed instead of dreamt), and analytical alternatives to inflectional forms are becoming more common (e.g. more polite instead of politer). British English is also undergoing change under the influence of American English, fuelled by the strong presence of American English in the media and the prestige associated with the US as a world power.[62][63][64]

Geographical distribution

Percentage of English native speakers

Percentage of English speakers by country

  80–100%
  60–80%
  40–60%
  20–40%
  0–20%
  Not available

As of 2016, 400 million people spoke English as their first language, and 1.1 billion spoke it as a secondary language.[65] English is the largest language by number of speakers.[66][circular reference] English is spoken by communities on every continent and on islands in all the major oceans.[67]

The countries where English is spoken can be grouped into different categories according to how English is used in each country. The “inner circle”[68] countries with many native speakers of English share an international standard of written English and jointly influence speech norms for English around the world. English does not belong to just one country, and it does not belong solely to descendants of English settlers. English is an official language of countries populated by few descendants of native speakers of English. It has also become by far the most important language of international communication when people who share no native language meet anywhere in the world.

Three circles of English-speaking countries

Braj Kachru distinguishes countries where English is spoken with a three circles model.[68] In his model,

  • the “inner circle” countries have large communities of native speakers of English,
  • “outer circle” countries have small communities of native speakers of English but widespread use of English as a second language in education or broadcasting or for local official purposes, and
  • “expanding circle” countries are countries where many people learn English as a foreign language.

Kachru bases his model on the history of how English spread in different countries, how users acquire English, and the range of uses English has in each country. The three circles change membership over time.[69]

Braj Kachru's Three Circles of English

Braj Kachru’s Three Circles of English

Countries with large communities of native speakers of English (the inner circle) include Britain, the United States, Australia, Canada, Ireland, and New Zealand, where the majority speaks English, and South Africa, where a significant minority speaks English. The countries with the most native English speakers are, in descending order, the United States (at least 231 million),[70] the United Kingdom (60 million),[71][72][73] Canada (19 million),[74]Australia (at least 17 million),[75] South Africa (4.8 million),[76]Ireland (4.2 million), and New Zealand (3.7 million).[77] In these countries, children of native speakers learn English from their parents, and local people who speak other languages and new immigrants learn English to communicate in their neighbourhoods and workplaces.[78] The inner-circle countries provide the base from which English spreads to other countries in the world.[69]

Estimates of the numbers of second language and foreign-language English speakers vary greatly from 470 million to more than 1 billion, depending on how proficiency is defined.[13] Linguist David Crystal estimates that non-native speakers now outnumber native speakers by a ratio of 3 to 1.[79] In Kachru’s three-circles model, the “outer circle” countries are countries such as the Philippines,[80]Jamaica,[81] India, Pakistan, Singapore,[82]Malaysia and Nigeria[83][84] with a much smaller proportion of native speakers of English but much use of English as a second language for education, government, or domestic business, and its routine use for school instruction and official interactions with the government.[85]

Those countries have millions of native speakers of dialect continua ranging from an English-based creole to a more standard version of English. They have many more speakers of English who acquire English as they grow up through day-to-day use and listening to broadcasting, especially if they attend schools where English is the medium of instruction. Varieties of English learned by non-native speakers born to English-speaking parents may be influenced, especially in their grammar, by the other languages spoken by those learners.[78] Most of those varieties of English include words little used by native speakers of English in the inner-circle countries,[78] and they may show grammatical and phonological differences from inner-circle varieties as well. The standard English of the inner-circle countries is often taken as a norm for use of English in the outer-circle countries.[78]

In the three-circles model, countries such as Poland, China, Brazil, Germany, Japan, Indonesia, Egypt, and other countries where English is taught as a foreign language, make up the “expanding circle”.[86] The distinctions between English as a first language, as a second language, and as a foreign language are often debatable and may change in particular countries over time.[85] For example, in the Netherlands and some other countries of Europe, knowledge of English as a second language is nearly universal, with over 80 percent of the population able to use it,[87] and thus English is routinely used to communicate with foreigners and often in higher education. In these countries, although English is not used for government business, its widespread use puts them at the boundary between the “outer circle” and “expanding circle”. English is unusual among world languages in how many of its users are not native speakers but speakers of English as a second or foreign language.[88]

Many users of English in the expanding circle use it to communicate with other people from the expanding circle, so that interaction with native speakers of English plays no part in their decision to use English.[89] Non-native varieties of English are widely used for international communication, and speakers of one such variety often encounter features of other varieties.[90] Very often today a conversation in English anywhere in the world may include no native speakers of English at all, even while including speakers from several different countries.[91]

Pluricentric English

Pie chart showing the percentage of native English speakers living in “inner circle” English-speaking countries. Native speakers are now substantially outnumbered worldwide by second-language speakers of English (not counted in this chart).

  US (64.3%)
  UK (16.7%)
  Canada (5.3%)
  Australia (4.7%)
  South Africa (1.3%)
  Ireland (1.1%)
  New Zealand (1%)
  Other (5.6%)

English is a pluricentric language, which means that no one national authority sets the standard for use of the language.[92][93][94][95] But English is not a divided language,[96] despite a long-standing joke originally attributed to George Bernard Shaw that the United Kingdom and the United States are “two countries separated by a common language”.[97] Spoken English, for example English used in broadcasting, generally follows national pronunciation standards that are also established by custom rather than by regulation. International broadcasters are usually identifiable as coming from one country rather than another through their accents,[98] but newsreader scripts are also composed largely in international standard written English. The norms of standard written English are maintained purely by the consensus of educated English-speakers around the world, without any oversight by any government or international organisation.[99]

American listeners generally readily understand most British broadcasting, and British listeners readily understand most American broadcasting. Most English speakers around the world can understand radio programmes, television programmes, and films from many parts of the English-speaking world.[100] Both standard and non-standard varieties of English can include both formal or informal styles, distinguished by word choice and syntax and use both technical and non-technical registers.[101]

The settlement history of the English-speaking inner circle countries outside Britain helped level dialect distinctions and produce koineised forms of English in South Africa, Australia, and New Zealand.[102] The majority of immigrants to the United States without British ancestry rapidly adopted English after arrival. Now the majority of the United States population are monolingual English speakers,[103][70] although English has been given official status by only 30 of the 50 state governments of the US.[104][105]

English as a global language