Your function H1 is not lazy enough. Closely following the instructions of the exercise I immediately come with:
(define (dan-then-dog) (cons "dan.jpg" (lambda () ???))) Can you fill in the question-marks? Can easily be done with stream-cons too: (define dan-then-dog-str (stream-cons "dan.jpg" ...)) but this is not according to the exercise, I think. In the exersize a stream is defined as a thunk. Jos > -----Original Message----- > From: users-boun...@racket-lang.org > [mailto:users-boun...@racket-lang.org] On Behalf Of Patrick Sweetman > Sent: jueves, 16 de mayo de 2013 14:31 > To: users@racket-lang.org > Subject: [racket] Problem Stream with alternating values > > 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 > ____________________ > Racket Users list: > http://lists.racket-lang.org/users ____________________ Racket Users list: http://lists.racket-lang.org/users
