rainbow-keys.el

(require 'faces)
(require 'color)
(require 'dash)

(unless (require 'xterm-color nil t)
  (require 'ansi-color))

(defvar rainbow-keys-font-lock-keywords
  '((":\\([-a-zA-Z0-9\\$\\?\\_\\*\\!\\.]+\\)/\\([-a-zA-Z0-9\\$\\?\\_\\*\\!]+\\)"
     (2 (colorize-ns-keyword 2)))
    (":\\([-a-zA-Z0-9\\$\\?\\_\\*\\!\\.]+\\)"
     (0 (colorize-keyword 1)))))

(defun hex-string-to-rgb (s)
  (let ((r (string-to-number (substring s 1 3) 16))
        (g (string-to-number (substring s 3 5) 16))
        (b (string-to-number (substring s 5 7) 16)))
    (list (/ r 255) (/ g 255) (/ b 255))))

(defun number-from-string (s)
  (/ (string-to-number (substring (md5 s) 0 2) 16) 255.0))

(defun colorize-match (color)
  (put-text-property
   (match-beginning 0) (match-end 0)
   'face `((:foreground ,color))))

(defun exclude (match)
  (or
   (equalp (get-text-property 0 'face (match-string match)) 'font-lock-string-face)
   (equalp (get-text-property 0 'face (match-string match)) 'font-lock-comment-face)))

(defun colorize-ns-keyword (match)
  (when (and (not (exclude match))
             (not (string-match "keys$" (match-string-no-properties match))))
    (let ((hue (number-from-string (match-string-no-properties match))))
      (colorize-match (apply 'color-rgb-to-hex (color-hsl-to-rgb hue 0.7 0.3))))))

(defun colorize-keyword (match)
  (when (and (not (exclude match))
             (not (string-match "^\\(keys\\|or\\|as\\|refer\\|require\\|exclude\\|refer-macros\\)$" (match-string-no-properties match))))
    (let ((hue (number-from-string (match-string-no-properties match))))
      (colorize-match (apply 'color-rgb-to-hex (color-hsl-to-rgb hue 1 0.3))))))

(defun rainbow-keys-turn-on ()
  "Turn on rainbow-keys-mode."
  (font-lock-add-keywords nil
                          rainbow-keys-font-lock-keywords
                          t))

(defun rainbow-keys-turn-off ()
  "Turn off rainbow-keys-mode"
  (font-lock-remove-keywords
   nil
   rainbow-keys-font-lock-keywords))

;;;###autoload
(define-minor-mode rainbow-keys-mode
  "Colorize clojure keywords"
  :lighter " Rainbow keys"
  (progn
    (if rainbow-keys-mode
        (rainbow-keys-turn-on)
      (rainbow-keys-turn-off))
    ;; Call font-lock-mode to refresh the buffer when used e.g. interactively
    (font-lock-mode 1)))

(provide 'rainbow-keys-mode)