;;; (C) 2008-2009 Dr. Gergo ERDI <http://gergo.erdi.hu/>

(in-package :alef)

(define-native/strict === (a b) ((t t) bool)
  (eql (payload a) (payload b)))

(parse-and-run
 `(,@*library*
   (deftype ring (t) (cons/ring t (ring t)))

   (define head/ring ((cons/ring y _))  y)
   (define tail/ring ((cons/ring _ ys)) ys)

   (define take/ring (0 _) nil)   
   (define take/ring (n (cons/ring y ys)) (cons y (take/ring (- n 1) ys)))   

   (define length/ring^ (x acc y)
     (if (=== x y)
         acc
         (length/ring^ x (+ acc 1) (tail/ring y))))
   
   (define length/ring (r)
     (length/ring^ r 1 (tail/ring r)))
   
   (define start ()
     (let ((r1 (cons/ring 0 r2))
           (r2 (cons/ring 1 r3))
           (r3 (cons/ring 2 r1)))
       (length/ring r1)))))