[plt-scheme] Re: HtDP 26.1.2

Thank you.  That helps a lot!
Dave

On Sat, Mar 21, 2009 at 3:53 PM, Chongkai Zhu <czhu at cs.utah.edu> wrote:

> Dave wrote:
>
>> Additional question --
>>
>> Is this how merge-neighbors supposed to process asymmetrical lists?
>>
>> (check-expect (merge-neighbors (list (list 3 7) (list 5))) (list 3 5
>> 7))
>>
>>
>>
>
> Yes.
>
> Chongkai
>
>  Thanks,
>>
>> Dave
>>
>> On Mar 21, 3:26 pm, dave yrueta <dyru... at gmail.com> wrote:
>>
>>
>>> Hi all --
>>>
>>> Question about HtDP function "merge-neighbors:"
>>>
>>> Link to exercise:
>>> http://www.htdp.org/2003-09-26/Book/curriculum-Z-H-33.html#node_sec_26.1
>>>
>>> The text describes the contract for "merge-neighbors" as a function
>>> which "merges pairs of neighboring lists. More specifically, it
>>> consumes a list of lists (of numbers) and merges neighbors. For
>>> example,
>>>
>>> (equal? (merge-all-neighbors (list (list 2) (list 5) (list 9) (list
>>> 3)))
>>>        (list (list 2 5) (list 3 9))) "
>>>
>>> In the example, however, it seems that in addition to merging pairs of
>>> neighboring lists, "merge-neighbors" also sorts each pair of lists in
>>> ascending order before combining them.  In other words --
>>>
>>> (check-expect (merge-all-neighbors (list (list 9) (list 1)) (list
>>> (list 1 9))?
>>>
>>>
>>>
>>
> Yes, merge-all-neighbors also sorts each pair of lists.
>
>  Further, suppose the function input is a list of list-of-numbers in
>>> descending order --
>>>
>>> (define list1 (list (list 9) (list 7) (list 5) (list 3))).
>>>
>>> In this case, does "merge-all-neighbors" evaluate list1 to (list (list
>>> 7 9) (list 3 5)) --
>>>
>>> -- or to (list (list 3 5) (list 7 9)).
>>>
>>>
>>>
>>
> The former, (list (list 7 9) (list 3 5)).
>
>
>  Thanks!
>>>
>>> Dave Yrueta
>>>
>>> _________________________________________________
>>>  For list-related administrative tasks:
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>>>
>>>
>> _________________________________________________
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>>
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>
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