Lisp (programming language)

Lisp (historically LISP, an abbreviation of "list processing") is a family of programming languages with a long history and a distinctive, fully parenthesized prefix notation. Originally specified in the late 1950s, it is the second-oldest high-level programming language still in common use, after Fortran. Lisp has changed since its early days, and many dialects have existed over its history. Today, the best-known general-purpose Lisp dialects are Common Lisp, Scheme, Racket, and Clojure.

Lisp was originally created as a practical mathematical notation for computer programs, influenced by (though not originally derived from) the notation of Alonzo Church's lambda calculus. It quickly became a favored programming language for artificial intelligence (AI) research. As one of the earliest programming languages, Lisp pioneered many ideas in computer science, including tree data structures, automatic storage management, dynamic typing, conditionals, higher-order functions, recursion, the self-hosting compiler, and the read–eval–print loop.

The name LISP derives from "LISt Processor". Linked lists are one of Lisp's major data structures, and Lisp source code is made of lists. Thus, Lisp programs can manipulate source code as a data structure, giving rise to the macro systems that allow programmers to create new syntax or new domain-specific languages embedded in Lisp.

The interchangeability of code and data gives Lisp its instantly recognizable syntax. All program code is written as s-expressions, or parenthesized lists. A function call or syntactic form is written as a list with the function or operator's name first, and the arguments following; for instance, a function f that takes three arguments would be called as (f arg1 arg2 arg3).

John McCarthy began developing Lisp in 1958 while he was at the Massachusetts Institute of Technology (MIT). He was motivated by a desire to create an AI programming language that would work on the IBM 704, as he believed that "IBM looked like a good bet to pursue Artificial Intelligence research vigorously." He was inspired by Information Processing Language, which was also based on list processing, but did not use it because it was designed for different hardware and he found an algebraic language more appealing. Due to these factors, he consulted on the design of the Fortran List Processing Language, which was implemented as a Fortran library. However, he was dissatisfied with it because it did not support recursion or a modern if-then-else statement (which was a new concept when Lisp was first introduced) .

McCarthy's original notation used bracketed "M-expressions" that would be translated into S-expressions. As an example, the M-expression car[cons[A,B]] is equivalent to the S-expression (car (cons A B)). Once Lisp was implemented, programmers rapidly chose to use S-expressions, and M-expressions were abandoned. M-expressions surfaced again with short-lived attempts of MLisp by Horace Enea and CGOL by Vaughan Pratt.

Lisp was first implemented by Steve Russell on an IBM 704 computer using punched cards. Russell was working for McCarthy at the time and realized (to McCarthy's surprise) that the Lisp eval function could be implemented in machine code.

According to McCarthy