numeronym minor mode

numeronym.el

(defun pas-numeronym ()
  "Replace last word with its numeronym.  eg.: 'accessibility' with 'a11y'."
  (interactive)
  (save-excursion
    (backward-word)
    (let ((count 0) (the-word (current-word)))
      (while (looking-at "[a-zA-Z']")
	(setq count (1+ count))
	(forward-char 1))
      (if (>= count 4)
	  (progn
	    (let ((numeronym (format "%s%d%s" (substring the-word 0 1) (- count 2) (substring the-word (1- count)))))
	      (search-backward the-word)
	      (replace-match numeronym)))))))

(define-minor-mode numeronym-mode
  "Automatically replace words as typed with their numeronym."
  :lighter " numeronym"
  (add-hook 'post-self-insert-hook
	    (lambda ()
	      (if (member (char-before) (string-to-list " .,:;?!"))
		  (pas-numeronym)))))