Re: scheme-question about unnesting list

[Thomas Morley]

Hi David,

2015-04-10 16:44 GMT+02:00 David Nalesnik <address@hidden>:
> Hi Harm,
>
> On Fri, Apr 10, 2015 at 7:28 AM, Thomas Morley <address@hidden>
> wrote:
>>
>> Hi,
>>
>> consider the following list:
>>
>> (define ls
>>   (list
>>    "a"
>>    (list
>>      (cons 'x "xx")
>>      (cons 'y "yy")
>>      (list 1 2 3))
>>    (cons 'z "zz")))
>>
>> I want to unnest it one level.
>> It can be done with the procedure 'unnest-list-one-lvl', which I
>> defined for that purpose:
>>
>> (define (unnest-list-one-lvl l)
>>   (append-map
>>     (lambda (e)
>>       (if (list? e)
>>           e
>>           (list e)))
>>     l))
>>
>> (unnest-list-one-lvl ls)
>>
>> -> ("a" (x . "xx") (y . "yy") (1 2 3) (z . "zz"))
>>
>>
>> Question:
>> Is there a better, easier way?
>>
>
> What's wrong with the way you're doing it?
>
> I mean, you could do something like this:
>
>  (define (unnest-a-level ls)
>    (let loop ((ls ls) (result '()))
>      (cond
>       ((null? ls) result)
>       ((list? (car ls)) (loop (cdr ls) (append result (car ls))))
>       (else (loop (cdr ls) (append result (list (car ls))))))))
>
> but it's not as concise!
>
> DN
>
>

thanks for it.
I think I'll stick to my own then. :)

Cheers,
  Harm