Re: ¨ (each) on defined function on array of empty arrays

[Dr . Jürgen Sauermann]

Hi Ben,

see below.

Jürgen


On 5/30/20 6:46 PM, Ben Harris wrote:
> [ Not sure if you deliberately left bug-apl off the recipient list:
> feel free to forward to the list if you want. ]
>
No. I probably just pushed reply instead of reply-to-all. I normally
want all communication
to be as transparent as possible, but sometimes I fail to  achieve that.
> On Sat, 30 May 2020, Dr. Jürgen Sauermann wrote:
>
>> not sure if it is an error. I suspect that the reason for the
>> difference you see is caused by the fact that the primitive ≡ and
>> your defined function 'depth' have different fill functions. The fill
>> function is a function applied to the empty arguments. The fill
>> function for ≡ is ≡ while the fill function for any defined function
>> (including depth) is { ⍵ } (or Z←B as IBM phrases it).
>
> I've looked briefly at the manual before realising that fill functions
> aren't relevant here.  The fill function is necessary when the right
> argument (R) to ¨ is empty, but here R is not empty, it's an array
> with two elements.  Each of those elements is empty, but R itself is not.
>
> So I think "each" should just pass each empty array to ≡ or depth as
> appropriate and it's only those functions that should pay attention to
> the emptiness of the arrays.  The description of the calling sequence
> for a defined function doesn't say anything special about empty
> arrays, so the empty arrays should just be passed on to ≡,so the two
> results should be the same.
>
I see. I will have another look at it, I did some tests with IBM APL2
after reading your first mail,
but everything related to empty values (or non-empty values containing
empty values) is
difficult to distinguish.
> Fill functions would matter if I evaluated ≡¨a or depth¨a, and indeed
> those differ (and I think give the correct results).
>