Icon (programming language)

This article is about the programming language. For pictogram or computer image, see Icon (computing). For Icon-L graphical programming of embedded systems, see de: iCon-L.

Icon

Paradigms	multi-paradigm: structured, text-oriented
Family	SNOBOL
Designed by	Ralph Griswold
First appeared	1977; 47 years ago (1977)
Stable release	9.5.24a / January 17, 2024; 3 months ago (2024-01-17)[1]
Typing discipline	dynamic
Website	www.cs.arizona.edu/icon
Major implementations
Icon, Jcon
Dialects
Unicon
Influenced by
SNOBOL, SL5, ALGOL
Influenced
Unicon, Python, Goaldi,[2] jq

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.^[3]