Язык Icon: от SNOBOL к современным генераторам.

A very high level programming language. the programming language

Icon is a very high level programming language based on the concept of "goal directed execution" in which code returns a "success" along with valid values, or a "failure", indicating that there is no valid data to return. The success and failure of a given block of code is used to direct further processing, whereas conventional languages would typically use boolean logic written by the programmer to achieve the same ends. Because the logic for basic control structures is often implicit in Icon, common tasks can be completed with less explicit code. Icon was designed by Ralph Griswold after leaving Bell Labs where he was a major contributor to the SNOBOL language. SNOBOL was a string processing language with what would be considered dated syntax by the standards of the early 1970s. After moving to the University of Arizona, he further developed the underlying SNOBOL concepts in SL5, but considered the result to be a failure. This led to the significantly updated Icon, which blends the short but conceptually dense code of SNOBOL like languages with the more familiar syntax of ALGOL inspired languages like C or Pascal. Like the languages that inspired it, the primary area of use of Icon is managing strings and textual patterns. String operations often fail, for instance, finding "the" in "world". In most languages, this requires testing and branching to avoid using a non valid result. In Icon most of these sorts of tests are simply unneeded, reducing the amount of code that must be written. Complex pattern handling can be done in a few lines of terse code, similar to more dedicated languages like Perl but retaining a more function oriented syntax familiar to users of other ALGOL like languages. Icon is not object oriented, but an object oriented extension named Idol was developed in 1996 which eventually became Unicon. It also inspired other languages, with its simple generators being especially influential; Icon's generators were a major inspiration for the Python language.

The original SNOBOL effort, retroactively known as SNOBOL1, launched in the fall of 1962 at the Bell Labs Programming Research Studies Department. The effort was a reaction to the frustrations of attempting to use the SCL language for polynomial formula manipulation, symbolic integration and studying Markov chains. SCL, written by the department head Chester Lee, was both slow and had a low level syntax that resulting in volumes of code for even simple projects. After briefly considering the COMIT language, Ivan Polonsky, Ralph Griswold and David Farber, all members of the six person department, decided to write their own language to solve these problems. The first versions were running on the IBM 7090 in early 1963, and by the summer had been built out and was being used across Bell. This led almost immediately to SNOBOL2, which added a number of built in functions, and the ability to link to external assembly language code. It was released in April 1964 and mostly used within Bell, but also saw some use at Project MAC. The introduction of system functions served mostly to indicate the need for user functions, which was the major feature of SNOBOL3, released in July 1964. SNOBOL3's introduction corresponded with major changes within the Bell Labs computing department, including the addition of the new GE 645 mainframe which would require a rewrite of SNOBOL. Instead, the team suggested writing a new version that would run on a virtual machine, named SIL for SNOBOL Intermediate Language, allowing it to be easily ported to any sufficiently powerful platform. This proposal was accepted as SNOBOL4 in September 1965. By this time, plans for a significantly improved version of the language emerged in August 1966. Further work on the language continued throughout the rest of the 1960s, notably adding the associative array type in later version, which they referred to as a table.