[plt-scheme] solution for exercise 11.2.4

ok maybe I found a solution:

(define (depth a-dl)
   (cond
     [(symbol? a-dl) 0]
     [else (+ 1 (depth (first a-dl)))]))
----------------------------------------
> CC: plt-scheme at list.cs.brown.edu
> From: matthias at ccs.neu.edu
> Subject: Re: [plt-scheme] solution for exercise 11.2.4
> Date: Tue, 10 Jun 2008 14:08:20 -0400
> To: cr-service at hotmail.it
> 
> 
> No. Try following the recipe.
> 
> On Jun 10, 2008, at 2:08 PM, carlo ambrogio wrote:
> 
>>
>> could it be right?
>>
>> (define (depth a-dl)
>>     (cond
>>     [(symbol? a-dl) 0]
>>     [else (list? (first a-dl)) (+ 1 (depth (rest a-dl)))]))
>>
>>
>> N.B. at the moment I'm away from my Dr.Scheme program...so I cannot  
>> run the code above...
>>
>> ----------------------------------------
>>> CC: plt-scheme at list.cs.brown.edu
>>> From: matthias at ccs.neu.edu
>>> Subject: Re: [plt-scheme] solution for exercise 11.2.4
>>> Date: Mon, 9 Jun 2008 21:10:25 -0400
>>> To: cr-service at hotmail.it
>>>
>>>
>>> Not true. You answered the question already and they are *trivial*
>>> question. I just want you to learn to think about what you're doing
>>> instead of just following something in a rote manner. Once you know
>>> how to think about it, you'll internalize and empower yourself to
>>> apply such things in situations where you never expected it.
>>>
>>> Try again. I expect an answer in 10 mins.
>>>
>>>
>>> On Jun 9, 2008, at 8:58 PM, carlo ambrogio wrote:
>>>
>>>>
>>>> ok now i'm stucked...
>>>> ----------------------------------------
>>>>> CC: plt-scheme at list.cs.brown.edu
>>>>> From: matthias at ccs.neu.edu
>>>>> Subject: Re: [plt-scheme] solution for exercise 11.2.4
>>>>> Date: Mon, 9 Jun 2008 20:38:29 -0400
>>>>> To: cr-service at hotmail.it
>>>>>
>>>>>
>>>>> Let me rephrase John's criticism: you jumped the gun and shot
>>>>> yourself.
>>>>>
>>>>> Just answer the questions that I asked. Not more, not less.
>>>>>
>>>>>
>>>>> On Jun 9, 2008, at 6:53 PM, carlo ambrogio wrote:
>>>>>
>>>>>>
>>>>>> the template could be:
>>>>>>
>>>>>> (define (depth a-dl)
>>>>>>   (cond
>>>>>>     [(symbol? a-dl) ...]
>>>>>>     [else ... (first a-dl) ... (depth (rest a-dl)) ...]))
>>>>>>
>>>>>> how many clauses does the data def have? (how many clauses must  
>>>>>> the
>>>>>> function def have?)
>>>>>>
>>>>>> I think 2 (the data can be a symbol or a list)
>>>>>>
>>>>>>
>>>>>>
>>>>>>
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