Making alistp matching plistp requirements

plistp is defined as

(defun plistp (object)
  "Non-nil if and only if OBJECT is a valid plist."
  (declare (pure t) (side-effect-free error-free))
  (let ((len (proper-list-p object)))
    (and len (zerop (% len 2)))))

For an equivalent alistp, checking cons cells with key and value,
how would the function be?