[plt-scheme] HTDP 16.3.4

On Sep 24, 2006, at 1:42 AM, wooks . wrote:

>
>
> I'm sure they can.
>
> The greater part of my brain has been occupied of late reading  
> these wonderful little books that have elephant drawings on them


My younger son used to report in grade school that his dad writes  
books about elephants. That is until they discovered his discussions  
of omega in second grade and his continuing insistence that he knew  
the biggest number of all. (At that point the math teacher got a  
lecture on transfinite ordinals and induction. But that's a different  
story.)


> So thank you for assisting me. I have been able to complete that  
> exercise.

Great! -- Matthias



>
>
>> From: Matthias Felleisen <matthias at ccs.neu.edu>
>> To: "wooks ." <wookiz at hotmail.com>
>> CC: plt-scheme at list.cs.brown.edu
>> Subject: Re: [plt-scheme] HTDP 16.3.4
>> Date: Fri, 22 Sep 2006 19:15:43 -0400
>>
>> Figure out what each expression in the template computes, just as  
>> the  recipe says. Then figure out how you can combine those values  
>> (lists)  into a single value (list). That's all. My freshmen can  
>> do it, w/o  help -- Matthias
>>
>>
>> On Sep 22, 2006, at 6:56 PM, wooks . wrote:
>>
>>>
>>>
>>>
>>>> From: Matthias Felleisen <matthias at ccs.neu.edu>
>>>> To: wooks . <wookiz at hotmail.com>
>>>> CC: plt-scheme at list.cs.brown.edu
>>>> Subject: Re: [plt-scheme] HTDP 16.3.4
>>>> Date: Fri, 22 Sep 2006 18:15:08 -0400
>>>>
>>>>
>>>> On Sep 22, 2006, at 5:28 PM, wooks . wrote:
>>>>
>>>>>
>>>>> I am looking at the last part of the section marked Challenge   
>>>>> which  requires a function
>>>>>
>>>>> ;;func-producing-list-of-lists: symbol directory-structure ->    
>>>>> [[symbol]]
>>>>> ;;produces a list of all the paths to files of the specified   
>>>>> name  in the directory structure.
>>>>
>>>> Where is the definition of [[symbol]]? Where is the definition  
>>>> of   "directory-structure"?
>>>>
>>>
>>> Well I was paraphrasing to make the statement of my problem more   
>>> concise. These are the definitions I have been working with.
>>>
>>> (define-struct file (name size content))
>>> (define-struct dir (name dirs files))
>>>
>>> ; DATA ANALYSIS
>>> ; A file is a structure:
>>> ;  (make-file n s x)
>>> ; where n is a symbol, s is a number, and x is some Scheme value.
>>> ;
>>> ; A list-of-files is either
>>> ;
>>> ;    1.  empty, or
>>> ;    2. (cons s lof) where s is a file and lof is a list of files.
>>> ;
>>> ; A dir is a structure:
>>> ;  (make-dir n ds fs)
>>> ; where n is a symbol, ds is a list of directories, and fs is a   
>>> list of files.
>>> ;
>>> ; A list-of-directories is either
>>> ;
>>> ;    1.  empty or
>>> ;    2. (cons s lod) where s is a dir and lod is a list of   
>>> directories.
>>> ;
>>> ;
>>>
>>>> Let's use the recipe. Presumably you have a template, one line  
>>>> in  one  function and three in the other keeping in mind that  
>>>> the  function(s)  really must return a list of paths. So
>>>>
>>>
>>> ....and these are the templates I wrote for the first 2 parts of   
>>> the problem .... find and find? both of which worked.
>>>
>>> (define (func-for-dir sym folder)
>>>  (....sym....
>>>       (dir-name folder) .....
>>>       (func-for-lods (dir-dirs  folder))....
>>>       (func-for-files (dir-files folder)))]))
>>>
>>> (define (func-for-lods alods)
>>>  (cond
>>>    [(empty? alods)....]
>>>    [else ....(func-for-dir (first alods)).....
>>>          (func-for-lods (rest alods))...]))
>>> (define (func-for-files alofs)
>>>  (cond
>>>    [(empty? alofs) ...]
>>>    [else .... (file-n (first alofs))
>>>          (file-s (first alofs))
>>>          (file-x (first alofs))
>>>          ....(func-for-files (rest alofs))..]))
>>>
>>>
>>>> -- cases without cross or self-references: return a list,   
>>>> distinguish  success from failure. done
>>>>
>>>> -- cases with self- or cross-references: each recursive/cross   
>>>> call  produces a list of paths to the "successes".  The answer  
>>>> is  a  combination of those partial results, plus the knowledge  
>>>> that  these  paths aren't complete. Since you figured out how to  
>>>> do one  path, I  bet that this part is a minor little step. It  
>>>> really is  just a help  function plus a line.
>>>>
>>>
>>> not on the same page with you yet Prof.
>>>
>>> After perusing Dr Bloch's webpages I started out
>>>
>>> ; OUTPUT TEMPLATE FOR FIND
>>> ; (define (func-returning-list-of-lists folder)
>>> ;   (cond
>>> ;     [..... empty]
>>> ;     [..... (cons (func-for-dir sym folder)
>>> ;                  (func-returning-list-of-lists folder))]))
>>>
>>> but couldn't figure out how to return successive paths.
>>> I'm not yet able to reconcile your input with my perception of  
>>> the  problem.
>>>
>>>
>>
>
>
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