Your view seems to be what Ken had in mind.
On this view, (x $ y) and (x $!.f y) are two very different verbs: one
that uses only atoms of y and one that uses fill.
If we allowed $ to have implied fill, we would be creating a chimera.
Perhaps we could define $!.'' (i. e. any empty fill) to indicate that
the fill should be implied from the type of y.
Henry Rich
On 2/20/2023 1:49 PM, Paul Jackson wrote:
I don't remember ever talking to Ken about this one, but I can tell you I
was quite upset when APL 2 changed the rules for reshape.
In my mind reshape would require special case handling to assume the need
for knowing the data type of the empty. Reshape doesn't ever provide
missing elements. It's sole task is to use the existing elements until
something the size requested is provided. There is no amount of looping
which can turn nothing into something, therefore I believe quite properly a
domain error.
On Mon, Feb 20, 2023, 6:27 AM Jan-Pieter Jacobs <[email protected]>
wrote:
Looking through the implementation of dev/eformat, I found this line which
puzzled me:
https://github.com/jsoftware/dev_eformat/blob/4c285152bb27c2bfcb474738ea3b839e4ce96d0d/eformat.ijs#L496
There's nothing wrong with that line, or with the fact it triggers an
error, but it does indicate that $ raises an error in a situation where {.
does not, i.e. reshaping an empty array errors, while overtaking from one
does not.
Indeed, 5 $ '' or 5$ 0$0 give an error, while 5 {. '' and 5 {. 0$0 just
work, producing arrays of 5 spaces or zeros as expected. 5 $!.'' '' also
works, as does 5$!.1 ''.
Why wouldn't $ be able to see the data type (and thereby, fill element) of
it's y argument, and fill accordingly? As far as I remember, any noun in J
has a datatype, and a fill element. As the the fill element is a scalar,
the dimensionality being different in the case of $ shouldn't matter
either.
Is there anything I'm missing, or is this really an inconsistency without
any reason for existence?
Best regards,
Jan-Pieter
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