Exercise 3.74 Zero crossings
nameless

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    (define (sign-change-detector value last-value)
  (cond ((and (< last-value 0) (>= value 0)) 1)
        ((and (>= last-value 0) (< value 0)) -1)
        (else 0)))

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

    (define (sign-change-detector value last-value)
  (cond ((and (< last-value 0) (>= value 0)) 1)
        ((and (>= last-value 0) (< value 0)) -1)
        (else 0)))

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

    (define (sign-change-detector value last-value)
  (cond ((and (< last-value 0) (>= value 0)) 1)
        ((and (>= last-value 0) (< value 0)) -1)
        (else 0)))

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

    (define (sign-change-detector value last-value)
  (cond ((and (< last-value 0) (>= value 0)) 1)
        ((and (>= last-value 0) (< value 0)) -1)
        (else 0)))

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