(provide 'add-hook)

(defun add-hook (hook-var hook-function)
  "Prepend hook-function to hook-var's value, if it is not already an element.
hook-var's value may be a single function or a list of functions."
  (if (boundp hook-var)
      (let ((value (symbol-value hook-var)))
	(if (and (listp value) (not (eq (car value) 'lambda)))
	    (and (not (memq hook-function value))
		 (set hook-var
		      (cons hook-function value)))
	  (and (not (eq hook-function value))
	       (set hook-var
		    (list hook-function value)))))
    (set hook-var hook-function)
    ))