Also, since you're not actually interested in the value of i, you
should probably use in-vector rather than in-range. The whole example
would be:
(for/list ([value (in-vector vector)]
#:when (< 0 (length value)))
value)
On Mon, Jul 13, 2015 at 3:18 PM, Jon Zeppieri <zeppi...@gmail.com> wrote:
> I think you're looking for #:when / #:unless.
>
> On Mon, Jul 13, 2015 at 3:12 PM, Pekka Niiranen
> <pekka.niira...@pp5.inet.fi> wrote:
>> Hello users,
>>
>> What is the proper design pattern to skip invalid values
>> when using for/list?
>>
>> The programs below fails because #:continue is not recognized:
>>
>> for/list ([i (in-range 0 1000)])
>> (let ((value (vector-ref vector i)))
>> (if (< 0 (length value))
>> value
>> #:continue)))
>>
>> Sure, I could bypass this limitation by building the list explicitely
>> with plain "for + cons" or:
>>
>> (define result-list
>> (for/list ([i (in-range 0 1000)])
>> (let ((value (vector-ref vector i)))
>> (if (< 0 (length value))
>> value
>> empty))))
>>
>> => then filter empties from result-list with another loop...
>>
>> -pekka-
>>
>>
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