[racket] please help to change vector to list

Hi All,

I know now that
helper v

passes v into 2nd lambda.

On Thu, Jun 2, 2011 at 6:11 AM, Yingjian Ma <yingjian.ma1955 at gmail.com>wrote:

> Hi Jos and ALL,
>
> The code is from website
>
> http://stackoverflow.com/questions/4175626/scheme-recursion-error
>
> I modified it.  It is not about homework.  I am learning and evaluating
> Racket.
>
> I use Language: racket; memory limit: 128 MB in DrRacket.
>
> The error I get is
>
>  > (test 'a '(b a c a))
> . . procedure application: expected procedure, given: '(b a c a) (no
> arguments)
>
> I found the problem.  I should use
>
> helper v
>
> not
>
>  helper (v)
>
> Here is another question.  In (lambda (ls), it seems ls took the value
> from v.  How does Racket know not pass x to ls as the argument?  Does it
> alway takes the right variable?  What happens if the first lambda has 3
> parameters and the 2nd lambda has 2 parameters?
>
> Also, I want code to keep all the letters that is not a.  It does not work
> for
> (test 'a #(b c a b a d)).  The result is '(c b).  If you know how to
> generalize it, please let me know.
>
> Thanks a lot.
>
>
> On Thu, Jun 2, 2011 at 4:10 AM, Jos Koot <jos.koot at telefonica.net> wrote:
>
>>  Whast you describe seems correct.
>> How about showing me yoyur code after deleting vector->list?
>>
>> If this is HOMEWORK, send it OFF LIST.
>>
>> What language did you use?
>>
>> Jos
>>
>>  ------------------------------
>> *From:* users-bounces at racket-lang.org [mailto:
>> users-bounces at racket-lang.org] *On Behalf Of *Yingjian Ma
>> *Sent:* 02 June 2011 08:45
>> *To:* users at racket-lang.org
>> *Subject:* [racket] please help to change vector to list
>>
>>   Hi ALL,
>>
>> I have this code
>>
>> (define test
>>   (lambda (x v)
>>     (define helper
>>       (lambda (ls)
>>         (cond
>>           ((empty? ls) '())
>>           ((empty? (rest ls)) '())
>>           ((equal? (second ls) x) (cons (first ls) (helper (rest
>> ls))))
>>           (else (helper (rest ls))))))
>>    (helper (vector->list v))))
>>
>> When I run it with
>> > (test 'a #(b a c a))
>> it returns
>> '(b c)
>>
>> Is there a way to use the list such as (test 'a '(b a c a))?  I tried to
>> delete vector->list from the last line of the code, but it did not work.
>> Why?
>>
>> Thanks a lot
>>
>>
>
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