sicp-ex-3.64

(define (stream-limit stream tolerance)
        (if (< (abs (- (stream-ref stream 1) (stream-ref stream 0))) tolerance)
                (stream-ref stream 1)
                (stream-limit (stream-cdr stream) tolerance)))

(define (stream-limit stream tolerance)
  (define (good-enough? a b)
    (< (abs (- a b)) tolerance))
  (define (loop s)
    (let ((a (stream-ref s 0))
          (b (stream-ref s 1)))
      (if (good-enough? a b)
          b
          (loop (stream-cdr s)))))
  (loop stream))

  
  
 (define (sub-streams stream1 stream2) 
     (stream-map - stream1 stream2)) 
  
 (define (one-order-difference stream) 
     (sub-streams (stream-cdr stream) stream)) 
  
 (define (stream-limit stream tolerance) 
     (define (iter tolerance-stream stream) 
         (if (<= (abs (stream-car tolerance-stream)) tolerance) 
             (stream-car stream) 
             (iter (stream-cdr tolerance-stream) (stream-cdr stream)))) 
     (iter (one-order-difference stream) (stream-cdr stream)))