In that case, you probably want to make use of in-value to bind
single-value sequences in your for*/list:
(for*/list ([(start end) (in-parallel 1 1000)]
[i (in-range start (sub1 end))]
[s (in-value (vector-ref vector i))]
[columns (in-value (string-split s ","))]
[col# (in-value (length columns))]
#:when (< 2 col#))
(first columns))
On Mon, Jul 13, 2015 at 3:46 PM, Pekka Niiranen
<pekka.niira...@pp5.inet.fi> wrote:
> Hello Sir.
>
> all true, but my example was bad simplification from the original code.
>
> The "ugly" part is to insert the multi-step function into #:when -clause
> and in case of success use function's internal parameter (columns) only.
> My imperative mind wants to use "continue" in the place "empty" below:
>
> (for*/list ([(start end) (in-parallel 1 1000)]
> [i (in-range start (sub1 end))])
> (let* ((columns (string-split (vector-ref vector i) ","))
> (col# (length columns)))
> (if (< 2 col#)
> (first columns)
> empty)))
>
>
>
> On 7/13/15 10:26 PM, Jon Zeppieri wrote:
>>
>> 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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>
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