ex60.scm

(load "stream-map.ss")
(load "ex59")

(define (scale-stream s f)
  (stream-map (lambda (x) (* x f)) s))
(define (mul-series s1 s2)
  (cons-stream (* (stream-car s1)
		  (stream-car s2))
	       (add-streams
		(scale-stream (stream-cdr s2) (stream-car  s1))
		(mul-series (stream-cdr s1) s2))))
(define x cosine-series)
(define y sine-series)
(define z (add-streams (mul-series x x) (mul-series y y)))
(define (print-stream s)
  (if (empty-stream? s)
      'done
      (begin (display (stream-car s))
	     (display " ")
	     (print-stream (stream-cdr s)))))
;; Yangyang Qq: 451107669			


(define (invert-unit-series s)
  (cons-stream 1
		(scale-stream 
		 (mul-series (stream-cdr s)
			     (invert-unit-series s))

		 -1)))
(define (div-series s1 s2)
  (if (= (stream-car s2) 0)
      (error "The denominator has a zero constant term")
      (mul-series s1 (invert-unit-series s2))))