Extensible programming

Extensible programming is a term used in computer science to describe a style of computer programming that focuses on mechanisms to extend the programming language, compiler and runtime environment. Extensible programming languages, supporting this style of programming, were an active area of work in the 1960s, but the movement was marginalized in the 1970s. Extensible programming has become a topic of renewed interest in the 21st century.any programming language in which programs and data are essentially interchangeable can be regarded as an extendible language. ... this can be seen very easily from the fact that Lisp has been used as an extendible language for years. Extensible programming is a term used in computer science to describe a style of computer programming that focuses on mechanisms to extend the programming language, compiler and runtime environment. Extensible programming languages, supporting this style of programming, were an active area of work in the 1960s, but the movement was marginalized in the 1970s. Extensible programming has become a topic of renewed interest in the 21st century. The first paper usually associated with the extensible programming language movement is M. Douglas McIlroy's 1960 paper on macros for higher-level programming languages. Another early description of the principle of extensibility occurs in Brooker and Morris's 1960 paper on the Compiler-Compiler. The peak of the movement was marked by two academic symposia, in 1969 and 1971. By 1975, a survey article on the movement by Thomas A. Standish was essentially a post mortem. The Forth programming language was an exception, but it went essentially unnoticed. As typically envisioned, an extensible programming language consisted of a base language providing elementary computing facilities, and a meta-language capable of modifying the base language. A program then consisted of meta-language modifications and code in the modified base language. The most prominent language-extension technique used in the movement was macro definition. Grammar modification was also closely associated with the movement, resulting in the eventual development of adaptive grammar formalisms. The Lisp language community remained separate from the extensible language community, apparently because, as one researcher observed, At the 1969 conference, Simula was presented as an extensible programming language. Standish described three classes of language extension, which he called paraphrase, orthophrase, and metaphrase (otherwise paraphrase and metaphrase being translation terms). Standish attributed the failure of the extensibility movement to the difficulty of programming successive extensions. An ordinary programmer might build a single shell of macros around a base language, but if a second shell of macros was to be built around that, the programmer would have to be intimately familiar with both the base language and the first shell; a third shell would require familiarity with the base and both the first and second shells; and so on. (Note that shielding the programmer from lower-level details is the intent of the abstraction movement that supplanted the extensibility movement.) Despite the earlier presentation of Simula as extensible, by 1975, Standish's survey does not seem in practice to have included the newer abstraction-based technologies (though he used a very general definition of extensibility that technically could have included them). A 1978 history of programming abstraction from the invention of the computer to the (then) present day made no mention of macros, and gave no hint that the extensible languages movement had ever occurred. Macros were tentatively admitted into the abstraction movement by the late 1980s (perhaps due to the advent of hygienic macros), by being granted the pseudonym syntactic abstractions. In the modern sense, a system that supports extensible programming will provide all of the features described below.