zz

(define get-sign
  (lambda(b)
    (if(char=? (string-ref b 0) #\-) -1 1)
    )
  )


(define find-point
  (lambda(s)
    (let((n (- (string-length s) 1)))
      (if(char=? (string-ref s  n) #\.)  n
         (if (= n 0)
             -1
             (find-point(substring s 0 n))
             )
         )
      )
    )
  )
(define rep->whole
  (lambda(s1 s2 b)
    (let((k (- (string-length s2) 1)))
         (let((pre (substring s2 0 k)) (lsb (string-ref s2 k)))
           (if (= k 0)
               (rep->get-v s1 lsb)
                (+ (* b (rep->whole s1 pre b)) (rep->get-v s1 lsb))
               )
           )
      )
    )
  )
(define rep->frac
  (lambda (s1 s2 b)
    (let((k (- (string-length s2) 1)))
         (let((pre (substring s2 0 k)) (lsb (string-ref s2 k)))
           (if (= k 0)
               (*(rep->get-v s1 lsb) (expt b (* -1 (+ k 1))))
               (+ (* (rep->get-v s1 lsb) (expt b (* -1 (+ k 1)))) (rep->frac s1 pre b))
               )
           )
      )
    )
  )
(define rep->get-v
  (lambda(s c)
    (let((k (- (string-length s) 1)))
      (if(= k -1)
          0
         (if(char=? (string-ref s k) c)
            k
            (rep->get-v (substring s 0 k) c)
            )
         )
      )
    )
  )
(define rep->number
  (lambda (s1 s2)
    (let((base (string-length s1)))
      (let((p (find-point s2)))
        (if(= p -1)
           (* (get-sign s2) (rep->whole s1 s2 base))
           (* (get-sign s2) (+ (rep->whole s1 (substring s2 0 p) base) (rep->frac s1 (substring s2 (+ p 1 )) base)))
           )
      )
      )
    )
  )