[racket] Problem Stream with alternating values

If you were to replace stream-cons with this function:

(define (not-stream-cons x y) (printf "x ~s y ~s\n" x y) 'something-random)

would it make sense to you what happens?

Robby


On Thu, May 16, 2013 at 7:30 AM, Patrick Sweetman <sweetmanpc at woosh.co.nz>wrote:

> I'm doing this problem:
>
> 6. Write a stream dan-then-dog, where the elements of the stream
> alternate between the strings "dan.jpg" and "dog.jpg" (starting with
> "dan.jpg"). More specically, dan-then-dog should be a thunk that when
> called produces a pair of "dan.jpg" and a thunk that when called
> produces a pair of "dog.jpg" and a thunk that when called... etc. Sample
> solution: 4 lines.
>
> and I cannot for the life of me understand why the following code does
> not produce a properly thunked stream. It evaluates the entries until it
> runs out of memory
>
> (define dan "dan.jpg")
> (define dog "dog.jpg")
>
> (define (dan-then-dog)
>   (define (H1 st0 b0)
>     (cond
>       [(= b0 1) (H1 (stream-cons dan st0) 0)]
>       [else     (H1 (stream-cons dog st0) 1)]
>       )
>     )
>   (H1 empty-stream 1))
>
> Can somebody please explain why my understanding of Racket streams is
> faulty?
>
> Thanks,
> Patrick Sweetman
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