Thank you Sir,
"in-value" did it.
Had I just had the instinct to search what the manual said;)
"Returns a sequence that produces a single value: v. This form is mostly
useful for let-like bindings in forms such as for*/list."
Irrelevant: There was a bug in last "example". Correct outer -loop was
(for*/list ([(start end) (in-parallel start-list end-list)]
-pekka-
On 7/13/15 10:51 PM, Jon Zeppieri wrote:
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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