This page is about displaying the word ‘lambda’ using the Greek letter. See also PrettySymbol.

Using prettify-symbols-mode

Emacs 24.4 introduced a minor mode called ‘prettify-symbols-mode’ .

( defun my-pretty-lambda () "make some word or string show as pretty Unicode symbols" (setq prettify-symbols-alist '( ( "lambda" . 955) ))) (add-hook 'scheme-mode-hook 'my-pretty-lambda) (global-prettify-symbols-mode 1)

The snippet above works only when ‘scheme-mode’ is on. Add more hooks if you wish to get other major modes working.

See also: http://ergoemacs.org/emacs/emacs_pretty_lambda.html

Using Character Composition

Library pretty-lambdada.el defines commands, including minor modes (local and global), that let you do this, either for specific modes or generally. The core display code is similar to the following snippet:

( defun pretty-lambdas () (font-lock-add-keywords nil `(( "(\\( lambda \\>\\)" (0 ( progn (compose-region (match-beginning 1) (match-end 1) ,(make-char 'greek-iso8859-7 107)) nil))))))

There are several versions of such snippets floating around. The one above is from LawrenceMitchell, modified from StefanMonnier’s rewrite of OliverScholz’s rewrite of LukeGorrie’s original pretty-lambda.el code (http://fresh.homeunix.net/~luke/misc/emacs/pretty-lambda.el).

And here is a variant by TrentBuck:

(font-lock-add-keywords 'emacs-lisp-mode '(( "(\\( lambda \\)\\>" (0 ( prog1 () (compose-region (match-beginning 1) (match-end 1) ?λ))))))

I stopped using pretty-lambda.el because Emacs was actually saving weird escape characters in my files such that when I reloaded them I’d still get lambda-symbols, even with this turned off. But it makes the files unreadable to other programs. Does anyone else have this problem, and know the fix? Since it’s all done in font-lock I didn’t expect the saved files to be affected. – LukeGorrie

This should happen only if the file was saved in the coding system Emacs Mule, because emacs-mule preserves the composition property. (Composition is actually part of Emacs’ m17n support.) Normally you should not use emacs-mule; however, auto-save files are saved in that coding system. So if you restore a file after a crash, for instance, you can get something like what you describe. A fix would be to use a hook to remove all composition properties before auto-saving. – OliverScholz

Using Font-Lock and Overlays

This library defines a minor mode that uses font-lock and overlays to display ‘lambda’ as the Greek letter: http://dishevelled.net/elisp/lambda-mode.el.

I use the misc-fixed font instead of the default, so lambda-mode displayed what looked like a Korean character. You can fix it by adding to your .emacs: (setq lambda-symbol (string #x1d77a))

Using an Image

Sugawara offers another approach: a minor mode that displays ‘lambda’ as a large Greek letter using an image.

( defvar big-lambda-image (create-image (base64-decode-string "/9j/4AAQSkZJRgABAQEASABIAAD/2wBDAAsICAoIBwsKCQoNDAsNERwSEQ8PESIZGhQcKSQrKigk JyctMkA3LTA9MCcnOEw5PUNFSElIKzZPVU5GVEBHSEX/2wBDAQwNDREPESESEiFFLicuRUVFRUVF RUVFRUVFRUVFRUVFRUVFRUVFRUVFRUVFRUVFRUVFRUVFRUVFRUVFRUVFRUX/wAARCAAwAEADASIA AhEBAxEB/8QAGgABAQEBAAMAAAAAAAAAAAAAAAUEAwIGB//EACgQAAEEAQIEBgMAAAAAAAAAAAEA AgMEERIhBTFhcQYUIjJBgRVRkf/EABcBAQEBAQAAAAAAAAAAAAAAAAABAwL/xAAcEQEBAQACAwEA AAAAAAAAAAAAAQIRIQMxQVH/2gAMAwEAAhEDEQA/APriIiAThZqvEKd5zxUtQzmP3CN4dj+Lyu1G XqklaRzmxyDDtJwSM7jsRsehWHiUbKlrh1qJgYWTCu7TtmN/p09g7QfpaYznXX1FVERZqIiICIiA ofiK6IvJV2t1vdZhkfv7I2yNy4/ZAHforM80deCSaZ4ZHG0uc48gBuSoTqE13g1+1Kwi5dj1MYec bW7xs+uZ6krfwyTU1r0lewIuNOyy5ThsR+yZgeOxGV2WNnF4qiIigIiIJd+N/EL8NIsd5WPE87iN n4PoZ13GT0AHyqiIurrmSfgixT/gpJa9hjxRc4vgmYwuEeTksdgbYJJB5YOPjffQuOvNllETo4Ne InPBaZG4GXYO4Gc4/eMrWi61ua7s7QREWav/2Q==" ) 'jpeg t)) ( defvar big-lambda-font-lock-keywords '(( ".+" (0 ( prog1 nil (big-lambda-remove-region (match-beginning 0) (match-end 0))))) ( "(\\( lambda \\)\\>" (0 ( prog1 nil (big-lambda-region (match-beginning 1) (match-end 1))))))) ( defun big-lambda-remove-region (beg end) "Remove big lambda property in region between BEG and END." ( let (pos) ( while (setq pos (text-property-any beg end 'display big-lambda-image)) (remove-text-properties pos (or (next-single-property-change pos 'display) end) '(display))))) ( defun big-lambda-region (beg end) "Add big lambda property in region between BEG and END." (put-text-property beg end 'display big-lambda-image)) ( define-minor-mode big-lambda-mode "Display big lambda." :lighter " Lambda" ( if big-lambda-mode ( progn ( save-restriction (widen) ( let ((font-lock-keywords big-lambda-font-lock-keywords)) (font-lock-fontify-buffer))) (font-lock-add-keywords nil big-lambda-font-lock-keywords)) (font-lock-remove-keywords nil big-lambda-font-lock-keywords) ( save-restriction (widen) ( let ((modified-p (buffer-modified-p))) (big-lambda-remove-region (point-min) (point-max)) (set-buffer-modified-p modified-p))))) ( defun big-lambda-mode-turn-on () "Turn on ` big-lambda-mode '." (interactive) (big-lambda-mode 1)) (add-hook 'emacs-lisp-mode 'big-lambda-mode-turn-on)

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