Error on 3.5.4 Streams and Delayed Evaluation

[naosense]

(define (solve f y0 dt)
  (define y (integral (delay dy) y0 dt))
  (define dy (stream-map f y))
  y)

print y: undefined; cannot use before initialization

[sorawee]

Please see Footnote 71 in the book, which states that you should see Section 4.1.6 and perhaps Exercise 4.18 :)

If you really want it to work without code transformation, try:

(define (solve f y0 dt)
  (define y (integral (delay (force dy)) y0 dt))
  (define dy (delay (stream-map f y)))
  y)

[naosense]

thanks

[io614]

Alternative solution:

(define (solve f y0 dt)
  (define y (integral-proc (delay (dy)) y0 dt))
  (define (dy) (stream-map f y))
  y)