(define (windows ls n)
   (let loop ((ls ls)
              (res '()))
     (if (null? (drop ls n))
         (cons (take-right ls n) res)
         (loop (drop-right ls 1) 
               (cons (take-right ls n) res)))))

;; (windows '(0 1 2 3 4 5 6 7 8 9) 4)
;; => ((0 1 2 3) (1 2 3 4) (2 3 4 5) (3 4 5 6) (4 5 6 7) (5 6 7 8) (6 7 8 9))

;; (windows '(0 1 2 3 4 5 6 7 8 9) 3)
;; => ((0 1 2) (1 2 3) (2 3 4) (3 4 5) (4 5 6) (5 6 7) (6 7 8) (7 8 9))