;; Terminate the loop, but return the accumulated count.
 (loop for i in '(1 2 3 stop-here 4 5 6)
       when (symbolp i) do (loop-finish)
       count i)
⇒  3

;; The preceding loop is equivalent to:
 (loop for i in '(1 2 3 stop-here 4 5 6)
       until (symbolp i)
       count i)
⇒  3

;; While LOOP-FINISH can be used can be used in a variety of 
;; situations it is really most needed in a situation where a need
;; to exit is detected at other than the loop's `top level'
;; (where UNTIL or WHEN often work just as well), or where some 
;; computation must occur between the point where a need to exit is
;; detected and the point where the exit actually occurs.  For example:
 (defun tokenize-sentence (string)
   (macrolet ((add-word (wvar svar)
                `(when ,wvar
                   (push (coerce (nreverse ,wvar) 'string) ,svar)
                   (setq ,wvar nil))))
     (loop with word = '() and sentence = '() and endpos = nil
           for i below (length string)
           do (let ((char (aref string i)))
                (case char
                  (#\Space (add-word word sentence))
                  (#\. (setq endpos (1+ i)) (loop-finish))
                  (otherwise (push char word))))
           finally (add-word word sentence)
                   (return (values (nreverse sentence) endpos)))))
⇒  TOKENIZE-SENTENCE

 (tokenize-sentence "this is a sentence. this is another sentence.")
⇒  ("this" "is" "a" "sentence"), 19

 (tokenize-sentence "this is a sentence")
⇒  ("this" "is" "a" "sentence"), NIL