Symbol (programming): Difference between revisions

Revision as of 02:30, 20 November 2011

Revision as of 02:30, 20 November 2011

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A symbol in [[Lisp (programming language)|Lisp]] is unique in a [[namespace]] (called package in [[Common Lisp]]). Symbols can be tested for equality with the function EQ. Lisp programs can generate new symbols at runtime. When Lisp reads data that contains textual represented symbols, existing symbols are referenced. If a symbol is unknown, the Lisp reader creates a new symbol.

In [[Common Lisp]] symbols have the following attributes: a name, a value, a function, a list of properties and a package. <ref>[http://www.lispworks.com/documentation/HyperSpec/Body/t_symbol.htm Common Lisp HyperSpec, system class Symbol]</ref>.

In [[Common Lisp]] symbols may use any characters, including whitespace, such as spaces and newlines. If a symbol contains a whitespace character it needs to be written as |this is a symbol|. Symbols can be used as identifiers for any kind of named programming constructs: variables, functions, macros, classes, types, goto tags and more.

Symbols can be interned in a package<ref>[http://www.lispworks.com/documentation/HyperSpec/Body/t_pkg.htm#package Common Lisp HyperSpec, system class Package]</ref>. Keyword symbols are self-evaluating<ref>[[Peter Norvig]]: ''Paradigms of Artificial Intelligence Programming: Case Studies in Common Lisp'', Morgan Kaufmann, 1991, ISBN 1-55860-191-0, [http://norvig.com/paip.html Web]</ref> and interned in the package named KEYWORD and.

==== Examples ====