ORF and values

As it turns out my previous post does not allow a values form as a place (the macro expands into invalid code).

So here is an updated version which behaves as follows.
When provided with a values form then for each place n, if n is nil
then n will be set to the nth value returned by the values-form.

eg.

(let ((a 1)
     b
     (c 3))
 (orf (values a b c) (values 4 2 5))
 (values a b c))

=> 1,2,3

And here it is in all it's glory.

(defmacro orf (place value-form &environment env)
 (multiple-value-bind (vars vals store-vars writer reader)
     (get-setf-expansion place env)
   (let ((tmp-var (loop repeat (length store-vars) collect (gensym))))
     `(let* (,@(mapcar 'list vars vals))
        (multiple-value-bind ,store-vars ,reader
          (multiple-value-bind ,tmp-var ,value-form
            ,@(loop for store in store-vars for val in tmp-var
                    collect `(unless  ,store (setf ,store ,val)))
            ,writer))))))