''&{:: doesn't do the same as 0&{:: in the general case though.
In favour of the proposal, think of how difficult life/J would be if {. }. {:
}: didn't "work" with scalars.
from the dictionary entry to take
"if y is an atom, it is replaced by ((#x)$1)$y"
2 2 {. 4 NB. 2 2 {. 1 1 $ 4
4 0
0 0
where atoms get special boosted powers compared to "undershaped" lists
2 2 {. 4 4
|length error
2 2 {. ,: 4 4
4 4
0 0
An argument against the proposal is that virtually all length errors have a
sensible alternative result. And "fixing" this one enhances the argument for
fixing all of them.
2 3 u 1 2 3 could be equivalent to u/@:,:
________________________________
From: Raul Miller <[email protected]>
To: "[email protected]" <[email protected]>
Sent: Wednesday, September 19, 2018 10:06 AM
Subject: Re: [Jprogramming] should 0 {:: scalar return that scalar instead of
being a length error?
Note also that ‘’ {:: 0 works, and also the typical case left argument for
{:: might be a boxed list.
—
Raul
On Tuesday, September 18, 2018, Henry Rich <[email protected]> wrote:
> By all means put it on the list.
>
> You are selecting along 1 axis from an argument that has 0 axes, which
> makes the length error reasonable.
>
> The question is, why does 0 { 0 not fail? Answer: because of the fine
> print in the definition. (0 { y) selects item number 0, and an atom has a
> single item, itself.
>
> (<0) { 5 fails, rightly, for the same reason 0 {:: 5 fails.
>
> It is important to get these edge cases right, and there's most often only
> one right way, so my assumption is that Roger did it the right way. I'll
> have to think it over.
>
> Henry Rich
>
>
>
> On 9/18/2018 8:05 PM, 'Pascal Jasmin' via Programming wrote:
>
>> I can add to request list.
>>
>> The argument for is that it is a source of "needless" errors. The error
>> applies also if there is a nested box structure, but the top level is an
>> atom.
>>
>> Perhaps there is a performance reason against it.
>>
>> I would doubt that existing code in the wild relies on the error for any
>> other purpose than to convert the scalar into a list of 1 item.
>> ----------------------------------------------------------------------
>> For information about J forums see http://www.jsoftware.com/forums.htm
>>
>
>
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