Удалить элемент на определенной позиции

(nconc (subseq list 0 (1- pos)) (nthcdr pos list))

(defun del-by-pos (lst pos)
  (if (null lst) nil
      (if (zerop pos) (cdr lst) (cons (car lst) (del-by-pos (cdr lst) (- pos 1))))))

(loop :for x :in list
      :for i :from 0
      :unless (= i pos)
      :collect x)

(defun del-by-pos (lst pos)
  (let ((res nil))
    (iter (for a in lst) (for c upfrom 0) (unless (= c pos) (collecting a into res)))
    res))
 
==> del-by-pos
 
(del-by-pos '(q w e r t y u i o p) 3)
 
==> (q w e T y u i o p)
 
(del-by-pos '(q w e r t y u i o p) 33)
 
==> (q w e r T y u i o p)
 
(del-by-pos '(q w e r t y u i o p) 0)
 
==> (w e r T y u i o p)
 
(del-by-pos '(q w e r t y u i o p) -50)
 
==> (q w e r T y u i o p)

(defun drop (w p &optional ac)
  (cond ((null w) (nreverse ac))
        ((zerop p) (append (nreverse ac) (cdr w)))
        ((drop (cdr w) (1- p) (cons (car w) ac)))))
 
> (drop '(1 2) 0)
(2)
> (drop '(1 2 3 4 5 6 7) 3)
(1 2 3 5 6 7)
> (drop '(1 2 3 4 5 6 7) 8)
(1 2 3 4 5 6 7)

(defun drop (w p)
  (loop for a in w for b from 0
        unless (= b p) collect a))
 
> (drop '(1 2 3 4 5 6 7) 0)
(2 3 4 5 6 7)
> (drop '(1 2 3 4 5 6 7) 3)
(1 2 3 5 6 7)
> (drop '(1 2 3 4 5 6 7) 8)
(1 2 3 4 5 6 7)

(defun drop (w p)
  (if (and w (plusp p))
      (cons (car w) (drop (cdr w) (1- p)))
      (cdr w)))
 
> (drop '(1 2 3 4 5 6 7) 0)
(2 3 4 5 6 7)
> (drop '(1 2 3 4 5 6 7) 3)
(1 2 3 5 6 7)
> (drop '(1 2 3 4 5 6 7) 8)
(1 2 3 4 5 6 7)

(defun drop (w p &optional ac)
  (if (and w (plusp p))
      (drop (cdr w) (1- p) (cons (car w) ac))
      (append (nreverse ac) (cdr w))))
 
> (drop '(1 2 3 4 5 6 7) 0)
(2 3 4 5 6 7)
> (drop '(1 2 3 4 5 6 7) 3)
(1 2 3 5 6 7)
> (drop '(1 2 3 4 5 6 7) 8)
(1 2 3 4 5 6 7)