CentralNotice From Wikipedia, the free encyclopedia Jump to navigation Jump to search Tree data structure representing the S-expression (* 2 (+ 3 4)) In computer programming , an S-expression (or symbolic expression , abbreviated as sexpr or sexp ) is an expression in a like-named notation for nested list ( tree -structured) data. S-expressions were invented for and popularized by the programming language Lisp , which uses them for source code as well as data. In the usual parenthesized syntax of Lisp, an S-expression is classically defined [1] as an atom, or an expression of the form ( x . y ) where x and y are S-expressions. This definition reflects LISP's representation of a list as a series of "cells", each one an ordered pair . In plain lists, y points to the next cell (if any), thus forming a list . The recursive clause of the definition means that both this...