Имеется список чисел, определить функционал, возвращающий список инкрементированных/декрементированных чисел

(defun f-incr (list &optional (i (lambda (x) (+ x 1))))
   (mapcar i list))
 
==> F-INCR
 
(f-incr '(1 2 3 4))
 
==> (2 3 4 5)
 
 
(defun f-decr (list &optional (d (lambda (x) (- x 1))))
   (mapcar d list))
 
==> F-DECR
 
(f-decr '(1 2 3 4))
 
==> (0 1 2 3)

(defun incdec (lst mthd)
  (let (rlst)
    (cond ((eq mthd 'inc)
       (dolist (x lst rlst)
         (setf rlst (nconc rlst (list (1+ x))))))
      ((eq mthd 'dec)
       (dolist (x lst rlst)
         (setf rlst (nconc rlst (list (1- x)))))))))
 
CL-USER> (incdec '(3 6 2) 'inc)
(4 7 3)
CL-USER> (incdec '(3 6 2) 'dec)
(2 5 1)
CL-USER> (incdec '(3 6 2) 'incorrect)
NIL

(defun incdec (lst mthd)
  (let (rlst)
    (dolist (x lst rlst)
      (cond
    ((eq mthd 'inc)
     (setf rlst (nconc rlst (list (1+ x)))))
    ((eq mthd 'dec)
     (setf rlst (nconc rlst (list (1- x)))))))))

(defun incdec (lst mthd)
  (let (rlst)
    (dolist (x lst rlst)
      (setf rlst
        (cond ((eq mthd 'inc)
           (nconc rlst (list (1+ x))))
          ((eq mthd 'dec)
           (nconc rlst (list (1- x)))))))))

(defun incdec (lst mthd)
  (let (rlst)
    (dolist (x lst rlst)
      (setf rlst
        (nconc rlst (list (if (eq mthd 'inc) (1+ x) (if (eq mthd 'dec) (1- x)))))))))

(defun incdec (lst &optional mthd)
  (let (rlst)
    (dolist (x lst rlst)
      (setf rlst
        (nconc rlst (list (if (eq mthd 'dec) (1- x) (1+ x))))))))

(defun incc (w) (mapcar #'1+ w))
 
> (incc '(0 1 2 3))
(1 2 3 4)

(defun decc (w) (mapcar #'1- w))
 
> (decc '(1 2 3 4))
(0 1 2 3)