Lisp (short for “LISt Processing”) is a family of programming languages, originally developed in the late 1950s by John McCarthy. Known for its unique, parenthesis-heavy syntax and powerful features for symbolic computation and recursive functions, Lisp has been influential in artificial intelligence research and the development of programming language theory.

Understanding Lisp Semantics

Lisp’s semantics revolve around the evaluation of S-expressions. Every expression in Lisp is either an atom or a list. Atoms (like numbers or symbols) evaluate to themselves or their bound values. Lists generally represent function applications, where the first element is interpreted as the function and the remaining elements as its arguments. The language embraces the idea that code and data share the same form—lists—enabling powerful metaprogramming through constructs like macros. Additionally, Lisp supports first-class functions and dynamic or lexical scoping rules that determine how variables are bound to values during evaluation.

S-expressions are the fundamental building blocks in Lisp, representing both code and data. They come in two forms:

• Atoms: The simplest elements, such as numbers, symbols, or strings, which evaluate to themselves or hold bound values. • Lists: Collections enclosed in parentheses, where the first element typically denotes a function and the remaining elements are its arguments.

This uniform structure enables powerful metaprogramming and recursive processing in Lisp.