Unnamed

(defun string-join (joiner strings)
  (string-join-accum joiner strings ""))
 
(defun string-join-accum (joiner strings accum)
  (cond ((not strings) accum)
        ((not (cdr strings)) (concat accum (car strings)))
        (t (string-join-accum joiner (cdr strings)
                              (concat accum (car strings) joiner)))))