Emacs lisp

Emacs Lisp

Paradigm	functional, meta, reflective
Family	Lisp
Designed by	Richard Stallman and Guy L. Steele, Jr.
Developer	GNU Project
First appeared	1985; 32 years ago (1985)
Stable release	25.1 / 17 September 2016; 4 months ago (2016-09-17)
Typing discipline	dynamic, strong
Scope	dynamic, optionally lexical
OS	Cross-platform
License	GNU GPLv3
Filename extensions	.el, .elc
Influenced by
Common Lisp, Maclisp

Emacs Lisp is a dialect of the Lisp programming language used as a scripting language by Emacs (a text editor family most commonly associated with GNU Emacs and XEmacs). It is used for implementing most of the editing functionality built into Emacs, the remainder being written in C (as is the Lisp interpreter itself). Emacs Lisp is also referred to as Elisp, although there is also an older, unrelated Lisp dialect with that name.

Users of Emacs commonly write Emacs Lisp code to customize and extend Emacs. Other options include the "Customize" feature that's been in GNU Emacs since version 20. Itself written in Emacs Lisp, Customize provides a set of preferences pages allowing the user to set options and preview their effect in the running Emacs session. When the user saves their changes, Customize simply writes the necessary Emacs Lisp code to the user's config file, which can be set to a special file that only Customize uses, to avoid the possibility of messing up the users own file.

Emacs Lisp can also function as a scripting language, much like the Unix Bourne shell or Perl, by calling Emacs in "batch mode". In this way it may be called from the command line or via an executable file, and its editing functions, such as buffers and movement commands are available to the program just as in the normal mode. No user interface is presented when Emacs is started in batch mode; it simply executes the passed-in script and exits, displaying any output from the script.

Emacs Lisp is most closely related to Maclisp, with some later influence from Common Lisp. It supports imperative and functional programming methods. Richard Stallman chose Lisp as the extension language for his rewrite of Emacs (the original used TECO as its extension language) because of its powerful features, including the ability to treat functions as data. Although the Common Lisp standard had yet to be formulated, Scheme existed at the time Stallman was rewriting Gosling Emacs into GNU Emacs. He chose not to use it because of its comparatively poor performance on workstations (as opposed to the minicomputers that were Emacs' traditional home), and he wanted to develop a dialect which he thought would be more easily optimized.