title: Symbolic Expression role: manual tags: #manual #reference #zettelstore syntax: zmk back: 00001012000000 00001012920516 00001012920525 00001012920528 00001012921000 00001012931000 backward: 00001012000000 00001012920516 00001012920525 00001012920528 00001012921000 00001012931000 box-number: 1 copyright: (c) 2020-present by Detlef Stern created: 20230403145644 forward: 00001012930500 lang: en license: EUPL-1.2-or-later modified: 20250627124639 published: 20250627124639 visibility: public A symbolic expression (also called *s-expression*) is a notation of a list-based tree. Inner nodes are lists of arbitrary length, while outer nodes are either primitive values (also called *atoms*) or the empty list. A symbolic expression is either * a primitive value (*atom*), or * a list of the form *(E1 E2 … En)*, where *Ei* is itself a symbolic expression, separated by space characters. An atom is a number, a string, or a symbol. Symbolic expressions are used in programming languages like LISP or Scheme, where they denote both data structures and the program itself. This allows a LISP or Scheme program to process LISP or Scheme programs. That property is also used within Zettelstore. Symbolic expressions are relatively easy to read, to parse, and to process. # See also * [Syntax](00001012930500) of symbolic expressions in the Zettelstore * [S-expression @ Wikipedia](https://en.wikipedia.org/wiki/S-expression)