Рекурсивное преобразование списка

(defun f (lst &optional (group-list '()) (counter 0) (group 1))
  (if (eql counter group)
      (cons group-list (f lst '() 0 (1+ group)))
      (if lst (f (cdr lst) `(,@group-list ,(car lst)) (1+ counter) group))))
 
CL-USER> (f '(1 2 3))
((1) (2 3))
CL-USER> (f '(1 2 3 4))
((1) (2 3))
CL-USER> (f '(a b c d e f g h i j k l m n))
((A) (B C) (D E F) (G H I J))

(defun f (lst &optional (group-list '()) (counter 0) (group 1))
  (cond ((= counter group) (cons group-list (f lst '() 0 (1+ group))))
    (t (cond ((null lst) nil)
         (t (f (cdr lst) `(,@group-list ,(car lst)) (1+ counter) group))))))

(defun f (l)
           (labels ((fun (l n)
                      (if l (cons
                             (loop for a from 1 to n
                                  for b in l collect b)
                             (fun (nthcdr n l) (1+ n))))))
             (fun l 1)))

(if test-form then-form [ else-form ])

(cond (test-form else-form)[(t else-form)])

;--- super if macro
; This macro allow the following forms:
;       (If a then b)   ==>  (cond (a b))
;       (If a thenret)  ==>  (cond (a))
;       (If a then b else c) ==> (cond (a b) (t c))
;       (If a then b b2              ==> (cond (a b b2) (c d d2) (t e))
;        elseif c then d d2
;        else e)

(do ((nums nil) (i 1 (1+ i)))
((> i 10) (nreverse nums))
(push i nums)) ==> (1 2 3 4 5 6 7 8 9 10)
 
(loop for i from 1 to 10 collecting i) ==> (1 2 3 4 5 6 7 8 9 10)

(defun f (L)
  (defun iter (lst group-list counter group)
    (cond ((= counter group) (cons group-list (iter lst '() 0 (1+ group))))
      (t (cond ((null lst) nil)
           (t (iter (cdr lst) `(,@group-list ,(car lst)) (1+ counter) group))))))
  (iter L '() 0 1))

#lang racket
(define (f L)
  (define (iter lst group-list counter group)
    (cond ((= counter group) (cons group-list (iter lst '() 0 (+ group 1))))
      (#t (cond ((null? lst) null)
                    (#t (iter (cdr lst) `(,@group-list ,(car lst)) (+ counter 1) group))))))
  (iter L '() 0 1))
 
> (f '(1 2 3))
'((1) (2 3))
> (f '(a b c d e f g h i j k l m n))
'((a) (b c) (d e f) (g h i j))
> (iter '(1 2 3) '() 0 1)
. . reference to an identifier before its definition: iter