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Facts Matter. Start Your Free Trial Today. Learn More in these related Britannica articles: computer programming language: Scripting languages. It was intended to have all the capabilities of earlier scripting languages. PERL provided many ways to state common operations and thereby allowed a programmer….

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Newer programming languages like Java and C have definite assignment analysis , a form of data flow analysis, as part of their static semantics. Once data has been specified, the machine must be instructed to perform operations on the data. For example, the semantics may define the strategy by which expressions are evaluated to values, or the manner in which control structures 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.


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

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 — discuss ] ——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. 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.

In static typing , all expressions have their types determined prior to when the program is executed, typically at compile-time. 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. Complete type inference has traditionally been associated with less mainstream languages, such as Haskell and ML. 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. 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. Weak typing allows a value of one type to be treated as another, for example treating a string as a number.

Strong typing prevents these program faults. An attempt to perform an operation on the wrong type of value raises an error. An alternative definition for "weakly typed" refers to languages, such as Perl and JavaScript , which permit a large number of implicit type conversions. 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.


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Some use the term strongly typed to mean strongly, statically typed , or, even more confusingly, to mean simply statically typed. Thus C has been called both strongly typed and weakly, statically typed. It may seem odd to some professional programmers that C could be "weakly, statically typed". 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.

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.

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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.

What is Programming Languages Research?

For example, in Java , a string literal is defined as an instance of the java. 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. 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.

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. 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.

One common trend in the development of programming languages has been to add more ability to solve problems using a higher level of abstraction. The earliest programming languages were tied very closely to the underlying hardware of the computer. As new programming languages have developed, features have been added that let programmers express ideas that are more remote from simple translation into underlying hardware instructions.

Because programmers are less tied to the complexity of the computer, their programs can do more computing with less effort from the programmer. This lets them write more functionality per time unit. Natural language programming 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". 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. 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.

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.

Programming for Linguists: Perl for Language Researchers

In some implementations that make use of the interpreter approach there is no distinct boundary between compiling and interpreting. Programs that are executed directly on the hardware usually run much faster than those that are interpreted in software. One technique for improving the performance of interpreted programs is just-in-time compilation. Here the virtual machine , just before execution, translates the blocks of bytecode which are going to be used to machine code, for direct execution on the hardware.

LINGUIST List Computational Linguistics: Hammond ()

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. Some languages may make the transition from closed to open; for example, Erlang was originally an Ericsson's internal programming language. Thousands of different programming languages have been created, mainly in the computing field.

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.