Easy way to merge plists?

Is there an easy way in Common Lisp to merge two plists? Or from another point of view: is there a way to remove duplicates from a plist? I know I can just append plists (and GETF will take the first one it finds), but I'd like to not keep accum开发者_开发知识库ulating unused keys as my app runs.

I'm thinking about something like (loop for p on my-plist by #'cddr ...), but there's often an easier way than my first thought!

You could start from this primitive version:

(defun merge-plist (p1 p2)
  (loop with notfound = '#:notfound
        for (indicator value) on p1 by #'cddr
        when (eq (getf p2 indicator notfound) notfound) 
        do (progn
             (push value p2)
             (push indicator p2)))
  p2)

CL-USER 104 > (merge-plist '(a 1 b 2 c 3) '(a 2 b 4))
(C 3 A 2 B 4)