A simple minor mode that can be added to emacs to automatically save a file while you are typing.

auto-save.el

(define-minor-mode auto-save-mode
  "Auto-save mode"
  nil " Reload" nil
  (if auto-save-mode
      ;; Edit hook buffer-locally.
      (add-hook 'post-command-hook 'auto-save nil t)
    (remove-hook 'post-command-hook 'auto-save t)))

(defun auto-save ()
  (when (buffer-modified-p)
    (save-buffer)))

(provide 'auto-save)