chinese rings in racket (baguenaudier ou baguenodier en français)

chinese-rings.rkt

(define rings-repl
    (let ((rings '(#f #f #f #f)))
      (λ ()
        (displayln rings)
        (set! rings (eval (list (read) `(quote ,rings))))
        (rings-repl))))

(define (b rings)
    (cond 
      ((null? rings) '())
      ((null? (cdr rings)) rings)
      ((car rings) (list* #t (not (cadr rings)) (cddr rings)))
      (#t  (cons #f (b (cdr rings))))))

(define (a rings)
    (cons (not (car rings)) (cdr rings)))

;> (rings-repl)
;(#f #f #f #f)
;a
;(#t #f #f #f)
;a
;(#f #f #f #f)
;b
;(#f #f #f #f)
;a
;(#t #f #f #f)
;b
;(#t #t #f #f)
;a
;(#f #t #f #f)
;b