[plt-scheme] Another request for help with book (HTDP)

Can we please not continue posting the Solutions url in public?
Our Teachers will be mighty upset if their students find their
way there, somehow. -- Matthias


On Jul 12, 2004, at 11:16 AM, Robby Findler wrote:

>   For list-related administrative tasks:
>   http://list.cs.brown.edu/mailman/listinfo/plt-scheme
>
> The code below is wrong and the sample solutions are correct. According
> to the problem spec in 11.2.2, tabulate-f
>
>   "consumes a natural number n and produces a list of n posns"
>
> Running your program for 0 will produce a list of 1 posn, but it should
> produce a list of 0 posns.
>
> I don't see any problems with 11.4.6 either.
>
> Robby
>
> At Sat, 10 Jul 2004 09:34:48 +0800, "Zhu Chongkai" wrote:
>>   For list-related administrative tasks:
>>   http://list.cs.brown.edu/mailman/listinfo/plt-scheme
>>
>>
>> My answer to exercise 11.2.2 is
>>
>> (define (tabulate-f n)
>>   (cond
>>     [(zero? n) (cons (make-posn 0 (f 0)) empty)]
>>     [else (cons (make-posn n (f n))
>>                 (tabulate-f (sub1 n)))]))
>>
>> But this means that:
>>
>> 1 HTDP exercise 11.4.6 should better be revised, using the same f of
>>   exercise 11.2.2
>> 2 the official solutions
>>   for these exercise are also wrong !!!!!!!
>>
>>
>> ======= 2004-07-08 11:12:21 Matt H?=======
>>
>>> Thanks again for helping me.
>>>
>>> I'm working in Chapter 11 of HTDP, and for exercise 11.2.2 I came up
>>> with this solution:
>>> ;; tabulate-f : number -> list-of-posns
>>> ;; product a list of n posns using f.
>>> (define (tabulate-f n)
>>>  (cond
>>>    [(zero? n) empty]
>>>    [else (cons (make-posn n (f n)) (tabulate-f (sub1 n)))]))
>>>
>>> Now, I'm not positive that this is correct because in exercise 11.4.6
>>> it says that (tabulate-f 3) should produce:
>>> (cons (make-posn 3 2.4)
>>>  (cons (make-posn 2 3.4)
>>>    (cons (make-posn 1 3.6)
>>>      (cons (make-posn 0 3.0)
>>>        empty))))
>>>
>>> But I get:
>>> (cons (make-posn 3 8)
>>>  (cons (make-posn 2 -1)
>>>    (cons (make-posn 1 -4) empty)))
>>>
>>> Is my solution for exercise 11.2.2 incorrect?
>>>
>>> Thank you for your time.
>>>
>>> On Wed, 7 Jul 2004 15:53:46 +0800, Zhu Chongkai 
>>> <mathematica at citiz.net> wrote:
>>>>
>>>> It is me again.
>>>>
>>>> Send details to my mailbox.
>>>>
>>>> ======= 2004-07-07 08:31:25 Matt H?=======
>>>>
>>>>>  For list-related administrative tasks:
>>>>>  http://list.cs.brown.edu/mailman/listinfo/plt-scheme
>>>>
>>>>
>>>>>
>>>>> Once again, I appear to be stuck. If someone is willing to help me
>>>>> with execise 11.2.2, I would be grateful.
>>>>>
>>>>> Thanks.
>>>>>
>>>>
>>>> = = = = = = = = = = = = = = = = = = = =
>>>>
>>>> Zhu Chongkai
>>>> http://www.websamba.com/mrmathematica
>>>>
>>>>
>>
>> = = = = = = = = = = = = = = = = = = = =
>>
>> Zhu Chongkai
>> http://www.websamba.com/mrmathematica