(defmacro with-context (&body body)
   `(let ((context (make-array 4 :element-type 'fixnum
                                 :initial-contents '(0 1 2 3))))
     ,@body))

(defun test-a ()
  (with-context
    (setf (aref context 3)
          (+ (aref context 0) (aref context 1)))
    context))

(defun context (n)
  (aref context n))