Lisp

Lisp is a family of programming languages with a long history, known for its distinctive approach to code and data. Designed by John McCarthy in 1958 for artificial intelligence research, Lisp stands for LISt Processing and adopts lists as its primary data structure. Programs are written in the form of S-expressions, which can be interpreted as both code and data, a property called homoiconicity. This enables powerful macro systems and metaprogramming.

Key features include dynamic typing, automatic memory management, first-class and higher-order functions, and a tradition of a minimal core with a rich library ecosystem. Most Lisp dialects use prefix notation and rely on recursion for looping. Many dialects support tail-call optimization or proper tail calls, making recursive patterns practical in functional styles. Macros are a hallmark; Common Lisp offers a sophisticated macro system, Scheme popularized hygienic macros, and Clojure adds modern platform integration and immutability-centric features.

Dialectally, the most widely known descendants are Common Lisp, Scheme, and newer variants like Clojure and Emacs Lisp for use in extensible editors. Lisp’s code-as-data paradigm heavily influenced macro systems in other languages, and its emphasis on symbolic computation and AI helped shape early and ongoing research in artificial intelligence programming languages.

Today, Lisp remains influential as a teaching language and in specialized domains, even though it is not as dominant in general-purpose programming as some later families. Emacs Lisp and Scheme implementations continue to be used in education and tooling, while Common Lisp maintains standardized specifications and practical implementations.