S-expression

In computing, s-expressions, sexprs or sexps (for 'symbolic expression') are a notation for nested list (tree-structured) data, 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 as In computing, s-expressions, sexprs or sexps (for 'symbolic expression') are a notation for nested list (tree-structured) data, 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 as The second, recursive part of the definition represents an ordered pair, which means that s-expressions are binary trees. The definition of an atom varies per context; in the original definition by John McCarthy, it was assumed that there existed 'an infinite set of distinguishable atomic symbols' represented as 'strings of capital Latin letters and digits with single embedded blanks' (i.e., character string and numeric literals). Most modern sexpr notations in addition use an abbreviated notation to represent lists in s-expressions, so that