(defmacro accum-uniq (f &body body)
  (let ((f (if (consp f) f (list f))))
    `(let (#1=#:acc)
       (flet ((,(car f) (#2=#:val) (pushnew #2# #1# ,@(cdr f))))
	 ,@body)
       #1#)))

(accum-uniq (a :test #'string=)
  (dotimes (i 100)
    (a (write-to-string (random 10)))))
;-> ("8" "0" "6" "2" "4" "5" "9" "7" "3" "1")