Functional programming. Lisp. 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.