Emacs: Display Lambda as λ

By Xah Lee. Date: . Last updated: .

Emacs 24.4 has a nice prettify-symbols-mode. In lisp modes, it displays lambda as “λ”. 〔►see Emacs 24.4 New Features (released 2014-10)

emacs pretty lambda 26110
emacs prettify-symbols-mode

Alt+x prettify-symbols-mode to activate it.

Open a emacs lisp file. (For example, Alt+x describe-functionCtrl+h f】 then type byte-compile, then click to open the lisp source code file.) Then, search for “lambda”. Then, Alt+x prettify-symbols-mode to watch it change.

Note that it only DISPLAYS the function named “lambda” as λ, it doesn't really change the text.

global-prettify-symbols-mode

To set it globally, put the following in your emacs init:

;; display “lambda” as “λ”
(global-prettify-symbols-mode 1)
emacs pretty lambda 44670
emacs prettify-symbols-mode

Adding Support for Pretty Lambda Mode

prettify-symbols-mode only works for major modes that supports it.

To add support, in your major mode, do:

(setq prettify-symbols-alist '(("lambda" . 955)))

The 955 is Unicode code point for λ in decimal. To find the Unicode code point of a char, type the char, then Alt+x describe-char. 〔►see Emacs: Unicode Tutorial

You can add other pairs. For example, to have arrow, do:

(setq prettify-symbols-alist
      '(
        ("lambda" . 955) ; λ
        ("->" . 8594)    ;         ("=>" . 8658)    ;         ("map" . 8614)    ;         ))

You can add it as a hook for any major mode. Here's a example:

(defun my-add-pretty-lambda ()
  "make some word or string show as pretty Unicode symbols"
  (setq prettify-symbols-alist
        '(
          ("lambda" . 955) ; λ
          ("->" . 8594)    ;           ("=>" . 8658)    ;           ("map" . 8614)   ;           )))

(add-hook 'clojure-mode-hook 'my-add-pretty-lambda)
(add-hook 'haskell-mode-hook 'my-add-pretty-lambda)
(add-hook 'shen-mode-hook 'my-add-pretty-lambda)
(add-hook 'tex-mode-hook 'my-add-pretty-lambda)

〔►see Emacs: Change Major Mode Keys

For other math symbols you might want to add, see:

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