Fibonacci Butt Sort

Let us discuss the various implementations of theFIBONACCI BUTT SORT.

This works in PLT scheme. It's not the best solution, but I wanted to use unfold.
[code](require srfi/1)
(define (make-cycle x)
  (let ((clist (apply circular-list x)))
    (lambda ()
      (begin0
        (car clist)
        (set! clist (cdr clist))))))
(define bbcode-select
  (let ((c (make-cycle (list o u))))
    (lambda (x)
      (if (string=? x " ")
          " "
          ((c) x)))))
(define (buttsort x)
    (b (i (apply string-append (unfold null? (lambda (y) (bbcode-select (car y))) cdr (regexp-split #rx"" x))))))[code]