valsetf.lisp

(defmacro valsetf (values-form . places)
  "Assigns the values of VALUES-FORM to the given PLACES.

   If VALUES-FORM yields more values than there are fields in PLACES, the
   remaining values are discarded.  If there are more fields in PLACES
   than there are values returned by the VALUES-FORM, the remaining
   fields are initialized to NIL."
  (assert places)
  (let* ((*gensym-counter* 1)
         (gensyms (mapcar #'(lambda (_)
                              (declare (ignore _))
                              (gensym "VALUE"))
                          places)))
    `(multiple-value-bind ,gensyms ,values-form
       (setf ,@(mapcan #'list places gensyms)))))