在Lisp中的str_replace？

(defun str-replace (string old new)
  (let ((start 0))
    (loop while (search old string :start2 start)
          do (setf start (1+ (search old string :start2 start)))
             (setf string (concatenate 'string (subseq string 0 (1- start)))
                           new
                           (subseq string start)))))

CL-USER> (str-replace "Hello, World!" "World" "Lisp")
"Hello, Lisp!"