(defun split (separator splittee)
  (let ((next-index (position separator splittee)))
    (if next-index
      (cons (subseq splittee 0 next-index) (split separator (subseq splittee (1+ next-index))))
      (list splittee))))

(defun replace-all (replacand replacee replacor)
  (let ((next-index (position replacand replacee)))
    (if next-index
      (concatenate 'string (subseq replacee 0 next-index) replacor (replace-all replacand (subseq replacee (1+ next-index)) replacor))
      replacee)))

(defun where-found (sought-letter the-string to-do-onroute to-do-on-leaf)
  (let ((next-index (position sought-letter the-string)))
    (if next-index
      (apply to-do-onroute
         (list (subseq the-string 0 next-index)
           (subseq the-string (1+ next-index))))
      (apply to-do-on-leaf (list the-string)))))

(defun split (separator splittee)
  (where-found separator splittee
           (lambda (pre-string post-string) (cons pre-string (split separator post-string)))
           (lambda (leaf-string) (list leaf-string))))

(defun replace-all (to-be-replaced-string the-patient-string the-replacement-string)
  (where-found to-be-replaced-string the-patient-string
           (lambda (pre-string post-string)
         (format t "pre: ~a post: ~a the-replacement-string: ~a ~%" pre-string post-string the-replacement-string)
         (concatenate 'string pre-string the-replacement-string (replace-all to-be-replaced-string post-string the-replacement-string)))
           (lambda (leaf-string) leaf-string)))

(format t "the cat is here: ~a ~%" (replace-all #Space "the cat is here" ""))
(format t "the cat is here: ~a ~%" (split #Space "the cat is here"))