Emacs Lisp

Emacs Lisp is a dialect of the Lisp programming language used by GNU Emacs. Most of the editing functionality built into Emacs is written in Emacs Lisp, with the remainder being written in C (as is the Lisp interpreter itself). Users of Emacs commonly write Emacs Lisp code to customize and extend Emacs.

Emacs Lisp

Library	lisp-mode
Command	emacs-lisp-mode
Builtin	yes
Auto-activates for	*.el, .emacs, _emacs

Emacs Lisp is also commonly referred to as "elisp" or "Elisp". Files containing Emacs Lisp code use the .el filename suffix; when byte-compiled, the same filename prefix is used but with the .elc filename suffix.

Emacs Lisp is a Lisp-2, which means that a single identifier (in Lisp terminology, "symbol") can simultaneously exist as ("be bound to") both a function and a variable.

Basic setup

You can customize the way Emacs edits and displays this and all other lisp languages with M-x customize-group RET lisp RET.

Helpful keybindings

[M-TAB]

Complete at point

[C-M-q]

Indent the S-expression following point

[C-M-x]

Evaluate the defun at point

Common customizations

Outlining

For Org-style outlining, add the following snippet to your Emacs configuration file.

;; Turn on outline minor mode
(add-hook 'emacs-lisp-mode-hook  'outline-minor-mode)

;; Add key bindings for Org-style outline cycling
(add-hook 'outline-minor-mode-hook
  (lambda ()
    (define-key outline-minor-mode-map [(control tab)] 'org-cycle)
    (define-key outline-minor-mode-map [(shift tab)] 'org-global-cycle)))

Now visit any elisp file (say M-x find-library RET outline) and keep pressing [S-TAB] and see what happens. Experiment similarly with [C-TAB].

Indentation

Add the following snippet to your Emacs configuration file, so that you don't have to indent deliberately. See M-x reindent-then-newline-and-indent.

(add-hook 'emacs-lisp-mode-hook
	  (lambda nil
	    (local-set-key [(return)] 'reindent-then-newline-and-indent)))

See also Lisp_editing and specially Parinfer for modes that help you keep the indentation (and the parens) automatically balanced.

Always keep parentheses balanced

See Skeleton#Keep some chars always balanced

Scope

By default elisp uses dynamic scope. Since Emacs 24 lexical scope has been added.
To use lexical binding, an Emacs-lisp source file must set a file-variable lexical-binding to t in the file header, e.g., by using a first line like:

   ;;; -*- lexical-binding: t -*-

Static Analysis

Elsa is the Emacs Lisp Static Analyzer. It analyses your code without loading or running it. It can track types and provide helpful hints when things don't match up before you even try to run the code.

See also

elisp-refs - intelligent code search for Emacs Lisp

elisp-refs (in MELPA) can find references to functions, macros or variables. Unlike a dumb text search, elisp-refs actually parses the code, so it's never confused by comments or variables with the same name as functions. This is particularly useful for finding all the places a function is used, or finding examples of usage. Interested readers may enjoy the author's blog post: Searching A Million Lines Of Lisp.

Convenient UI to edit lists

refine provides a convenient UI for editing variables. Refine is not for editing files, but for changing elisp variables, particularly big lists (such as hooks).

Lisp editing

lisp editing here on wikemacs.

External links

• Emacs Lisp manual
• Programming in elisp, libreplanet.org wiki
• Rules on Elisp coding, on nongnu.org
• Emacs Lisp Style Guide, on Github