Basa program

Basa programnyaétabasa jieunannu bisa dipaké keurngadalikeunparipolah hiji mesin, utamanakomputer.Basa program, sapertibasa alami, dihartikeun ku aturansintaksisjeungsemantikkeur ngajelaskeun struktur jeung hartina. Loba basa program nu mibanda sababaraha wanda dina nuliskeunsintaksjeungsemantik; sababaraha basa program ngan dihartikeun ku sawanda dina cara maké sacara resmi.
Basa program dipaké keur mantuankomunikasidina raraga ngokolakeun pangaweruh tur nembongkeunalgoritmakalawan présisi. Sababaraha pangarang méré watesan nu leuwih heureut yén "basa program" nyaéta basa nu bisa dipaké keur ngagambarkeunsakabehalgoritmanu mungkin;kadangkala watesan "basa komputer" dipaké keur basa jieunan nu leuwih heureut.
Rébuan basa program nu béda-bedageus dijieun, tur méh unggal taun ngahasilkeun basa program nu anyar.
Sifat penting keur nangtukeun pilihan basa program nyaéta:
Basa non-komputasi, sapertibasa markupsigaHTMLatawaformal grammarsigaBNF, ilaharna teu disebut basa program. Ilaharna basa program ditambahkeun kana basa non-itungan ieu.
Kaperluan utama basa program nyaéta keur méré paréntah kana komputer. Saperti, basa program béda jeung éksprési jalma nu mana merlukeun présisi nu luhur tur lengkep. Waktu ngagunakan hiji basa alam keur ngobrol jeung jalma séjén, pangarang jeung nu ngobrol bisa bingung tur nyieun saeutik kasalahan, sarta duana masih bisa ngarti. béda jeung komputer nu sarua jeung naon anu diparéntahkeun ka manéhna, teu bisa ngarti kana kode nu nyieun program "nu dimaksud" keur nulis. Kombinasi harti basa,program, jeung asupan program kudu sacara husus ngartikeun paripolah luar nu bakal kajadian lamun éta program dijalankeun.
Loba basa geus dirancang ti anggalna, dirobah pikeun minuhan kabutuhan anyar, digabungkeun jeung basa séjén, sarta pamustunganana ditinggalkeun. Sanaos aya usaha pikeun ngararancang hiji basa komputer "universal" anu tiasa dianggo pikeun sadaya tujuan, aranjeunna sadayana gagal ditampi dina peran ieu.Kabutuhan pikeun rupa-rupa basa komputer bijil tina rupa-rupa basa kontéks anu digunakeunana :
One common trend in the development of programming languages has been to add more ability to solve problems using a higher level ofabstraction.  The éarliest programming languages were tied very closely to the underlying hardware of the computer.  As new programming languages have developed, féatures have been added that let programmers express idéas that are more removed from simple translation into underlying hardware instructions.  Because programmers are less tied to the needs of the computer, their programs can do more computing with less effort from the programmer.  This lets them write more programs in the same amount of time.
Natural language processorshave 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 Dijkstratook the position that the use of a formal language is essential to prevent the introduction of méaningless constructs, and dismissed natural language programming as "foolish."Alan Perliswas similarly dismissive of the idéa.
A programming language's surface form is known as itssyntax.  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 moregraphicalin nature, using spatial 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 méaning given to a combination of symbols is handled by semantics.  Since most languages are textual, this article discusses textual syntax.
Programming language syntax is usually defined using a combination ofregular expressions(forlexicalstructure) andBackus-Naur Form(forgrammaticalstructure).  Below is a simple grammar, based onLisp:
expression ::= atom   | listatom       ::= number | symbolnumber     ::= [+-]?['0'-'9']+symbol     ::= ['A'-'Z''a'-'z'].*list       ::= '(' expression* ')'
This grammar specifies the following:
The following are examples of well-formed token sequences in this grammar: '12345', '()', '(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 exhibitundefined behavior.  Even when a program is well-defined within a language, it may still have a méaning that is not intended by the person who wrote it.
Usingnatural languageas an example, it may not be possible to assign a méaning to a grammatically correct sentence or the sentence may be false:
The following C language fragment is syntactically correct, but performs an operation that is not semantically defined (becausepis anull pointer, the operationsp->réalandp->imhave no méaning):
The grammar needed to specify a programming language can be classified by its position in theChomsky hierarchy.  The syntax of most programming languages can be specified using a Type-2 grammar, i.e., they arecontext-free grammars.
A type system defines how a programming language classifies values and expressions intotypes, how it can manipulate those types and how they interact.  This generally includes a description of thedata structuresthat can be constructed in the language.  The design and study of type systems using formal mathematics is known astype theory.
Internally, alldatain modérn digital computers are stored simply as zeros or ones (binary).
A language istypedif operations defined for one data type cannot be performed on values of another data type.For example, "this text between the quotes" is a string. In most programming languages, dividing a number by a string has no méaning. Most modérn programming languages will therefore reject any program attempting to perform such an operation.  In some languages, the méaningless operation will be detected when the program is compiled ("static" type checking), and rejected by the compiler, while in others, it will be detected when the program is run ("dynamic" type checking), resulting in a runtimeexception.
A special case of typed languages are thesingle-typelanguages.  These are often scripting or markup languages, such asRexxorSGML, and have only one data type — most commonly character strings which are used for both symbolic and numeric data.
In contrast, anuntyped language, such as mostassembly languages, allows any operation to be performed on any data, which are generally considered to be sequences of bits of various lengths.High-level languages which are untyped includeBCPLand some varieties ofForth.
In practice, while few languages are considered typed from the point of view oftype theory(verifying or rejectingalloperations), most modérn languages offer a degree of typing.Many production languages provide méans to bypass or subvert the type system.
Instatic typingall expressions have their types determined prior to the program being run (typically at compile-time).  For example, 1 and (2+2) are integer expressions; they cannot be passed to a function that expects a string, or stored in a variable that is defined to hold dates.
Statically-typed languages can bemanifestly typedortype-inferred.  In the first case, the programmer must explicitly write types at certain textual positions (for example, at variabledeclarations).  In the second case, the compilerinfersthe types of expressions and declarations based on context.  Most mainstréam statically-typed languages, such asC++andJava, are manifestly typed.  Complete type inference has traditionally been associated with less mainstréam languages, such asHaskellandML.  However, many manifestly typed languages support partial type inference; for example,JavaandC#both infer types in certain limited cases.Dynamic typing, also calledlatent typing, determines the type-safety of operations at runtime; in other words, types are associated withruntime valuesrather thantextual expressions.As with type-inferred languages, dynamically typed languages do not require the programmer to write explicit type annotations on expressions.  Among other things, this may permit a single variable to refer to values of different types at different points in the program execution.  However, type errors cannot be automatically detected until a piece of code is actually executed, making debugging more difficult.Ruby,Lisp,JavaScript,  andPythonare dynamically typed.
Weak typingallows a value of one type to be tréated as another, for example tréating a string as a number.This can occasionally be useful, but it can also allow some kinds of program faults to go undetected atcompile time.
Strong typingprevents the above.  Attempting to mix types raises an error.Strongly-typed languages are often termedtype-safeorsafe.  Type safety can prevent particular kinds of program faults occurring (because constructs containing them are flagged at compile time).
An alternative definition for "weakly typed" refers to languages, such asPerl,JavaScript, andC++which permit a large number of implicit type conversions; Perl in particular can be characterized as a dynamically typed programming language in which type checking can take place at runtime. Seetype system.  This capability is often useful, but occasionally dangerous; as it would permit operations whose objects can change type on demand.
Strongandstaticare generally considered orthogonal concepts, but usage in the literature differs.  Some use the termstrongly typedto méanstrongly, statically typed, or, even more confusingly, to méan simplystatically typed.  ThusChas been called both strongly typed and wéakly, statically typed..
Once data has been specified, the machine must be instructed to perform operations on the data.  Theexecution semanticsof a language defines how and when the various constructs of a language should produce a program behavior.
For example, the semantics may define thestrategyby which expressions are evaluated to values, or the manner in whichcontrol structuresconditionally execute statements.
Most programming languages have an associatedcore 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.
A language's core library is often tréated as part of the language by its users, although the designers may have tréated it as a separate entity.  Many language specifications define a core that must be made available in all implementations, and in the case of standardized languages this core library may be required.  The line between a language and its core library therefore differs from language to language.  Indeed, some languages are designed so that the méanings of certain syntactic constructs cannot even be described without referring to the core library.  For example, inJava, a string literal is defined as an instance of thejava.lang.Stringclass; similarly, inSmalltalk, ananonymous functionexpression (a "block") constructs an instance of the library'sBlockContextclass.  Conversely,Schemecontains 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.
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 languagespecificationandimplementation.
Thespecificationof a programming language is intended to provide a definition that languageusersandimplementorscan use to determine the behavior of aprogram, given itssource code.
A programming language specification can take several forms, including the following:
Animplementationof a programming language provides a way to execute that program on one or more configurations of hardware and software.  There are, broadly, two approaches to programming language implementation:compilationandinterpretation.  It is generally possible to implement a language using either technique.
The output of acompilermay be executed by hardware or a program called an interpreter.  In some implementations that maké use of the interpreter approach there is no distinct boundary between compiling and interpreting.  For instance, some implementations of theBASIC programming languagecompile and then execute the source a line at a time.
Programs that are executed directly on the hardware usually run several orders of magnitude faster than those that are interpreted in software.
One technique for improving the performance of interpreted programs isjust-in-time compilation.  Here thevirtual machinemonitors which sequences ofbytecodeare frequently executed and translates them to machine code for direct execution on the hardware.
The first programming languages predate the modérn computer. The 19th century had "programmable"loomsandplayer pianoscrolls which implemented what are today recognized as examples ofdomain-specific programming languages.  By the beginning of the twentieth century, punch cards encoded data and directed mechanical processing.  In the 1930s and 1940s, the formalisms ofAlonzo Church'slambda calculusandAlan Turing'sTuring machinesprovided mathematical abstractions for expressingalgorithms; the lambda calculus remains influential in language design.
In the 1940s, the first electrically powered digital computers were créated. The computers of the éarly 1950s, notably theUNIVAC Iand theIBM 701usedmachine language programs.First generationmachine language programming was quickly superseded by asecond generationof programming languages known asAssembly languages.  Later in the 1950s, assembly language programming, which had evolved to include the use ofmacro instructions, was followed by the development of three higher-level programming languages:FORTRAN,LISP, andCOBOL. Updated versions of all of these are still in general use, and importantly, éach has strongly influenced the development of later languages.At the end of the 1950s, the language formalized asAlgol 60was introduced, and most later programming languages are, in many respects, descendants of Algol.The format and use of the éarly programming languages was héavily influenced by theconstraints of the interface.
The period from the 1960s to the late 1970s brought the development of the major language paradigms now in use, though many aspects were refinements of idéas in the very firstThird-generation programming languages:
éach of these languages spawned an entire family of descendants, and most modérn languages count at léast one of them in their ancestry.
The 1960s and 1970s also saw considerable debate over the merits ofstructured programming, and whether programming languages should be designed to support it.Edsger Dijkstra, in a famous 1968 letter published in theCommunications of the ACM, argued thatGOTOstatements should be eliminated from all "higher level" programming languages.
The 1960s and 1970s also saw expansion of techniques that reduced the footprint of a program as well as improved productivity of the programmer and user. Thecard deckfor an éarly4GLwas a lot smaller for the same functionality expressed in a3GL deck.
The 1980s were yéars of relative consolidation.C++combined object-oriented and systems programming.  The United States government standardizedAda, a systems programming language intended for use by defense contractors. In Japan and elsewhere, vast sums were spent investigating so-called"fifth generation" languagesthat incorporated logic programming constructs. The functional languages community moved to standardize ML and Lisp.  Rather than inventing new paradigms, all of these movements elaborated upon the idéas invented in the previous decade.
One important trend in language design during the 1980s was an incréased focus on programming for large-scale systems through the use ofmodules, or large-scale organizational units of code.Modula-2, Ada, and ML all developed notable module systems in the 1980s, although other languages, such asPL/I, alréady had extensive support for modular programming. Module systems were often wedded togeneric programmingconstructs.
The rapid growth of theInternetin the mid-1990's créated opportunities for new languages.Perl, originally a Unix scripting tool first reléased in 1987, became common in dynamicWeb sites.Javacame to be used for server-side programming.  These developments were not fundamentally novel, rather they were refinements to existing languages and paradigms, and largely based on the C family of programming languages.
Programming language evolution continues, in both industry and reséarch.  Current directions include security and reliability verification, new kinds of modularity (mixins,delegates,aspects), and database integration.
The4GLsare examples of languages which are domain-specific, such asSQL, which manipulates and returnssetsof data rather than the scalar values which are canonical to most programming languages.Perl, for example, with its 'here document' can hold multiple 4GL programs, as well as multiple JavaScript programs, in part of its own perl code and use variable interpolation in the 'here document' to support multi-language programming.
It is difficult to determine which programming languages are most widely used, and what usage méans varies by context.  One language may occupy the gréater number of programmer hours, a different one have more lines of code, and a third utilize the most CPU time.  Some languages are very popular for particular kinds of applications.  For example,COBOLis still strong in the corporate data center, often on largemainframes;FORTRANin engineering applications;Cin embedded applications and operating systems; and other languages are regularly used to write many different kinds of applications.
Various methods of méasuring language popularity, éach subject to a different bias over what is méasured, have been proposed:
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 idéas in circulation at the time.  Idéas that originate in one language will diffuse throughout a family of related languages, and then léap suddenly across familial gaps to appéar 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 multiplethreadsin parallel).Pythonis an object-orientedscripting language.
In broad strokes, programming languages divide intoprogramming paradigmsand a classification byintended domain of use.  Paradigms includeprocedural programming,object-oriented programming,functional programming, andlogic programming; some languages are hybrids of paradigms or multi-paradigmatic.  Anassembly languageis not so much a paradigm as a direct modél 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).Some general purpose languages were designed largely with educational goals.
A programming language may also be classified by factors unrelated to programming paradigm. For instance, most programming languages useEnglish languagekeywords, while aminority do not. Other languages may be classified as beingesotericor not.
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