Lisp programming language. The interchangeability of code and data also 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 might be called using (f arg1 arg2 arg3). John McCarthy and Steve Russell Information Processing Language was the first AI language, from 1955 or 1956, and already included many of the concepts, such as list-processing and recursion, which came to be used in Lisp.