SICP 問題 3.76

前回のデータと比べて平均化する．

(define (smooth stream)
  (cons-stream (average (car stream) 0)
               (stream-map average
                           (stream-cdr stream)
                           stream)))

(define (make-zero-crossings sense-data)
  (let ((smooth-data (smooth sense-data)))
    (stream-map sign-change-detector
                smooth-data
                (cons-stream 0 smooth-data))))