On Mon, 26 Jul 2021, Raul Miller wrote:
I think that the problem here would be in defining vu to work in your examples.
I definitely don't think that's the problem!
Here are some definitions; untested, but hopefully illustrative:
',': $@>@{. $ >@{:
'{.': >@{: , }.@>@{.
'}.': {.@>@{. , >@{:
-E
PS. I am no longer certain about the dyadic case. I'm not sure if it can
work the way I originally proposed it; I think it might work given
knowledge of u, but am not certain of that either.
If you could do that, I think you would have something.
Without that, though, we would need a different approach.
Thanks,
--
Raul
On Mon, Jul 26, 2021 at 3:57 PM Elijah Stone <[email protected]> wrote:
'Structural under' is an extension to under (&. &.:) that allows it to
operate on otherwise uninvertible structure-changing verbs. It is
implemented in dzaima/apl (https://github.com/dzaima/APL/).
For example:
-&.{. 1 2 3 4 NB. take the head, negate it, reaffix it to the rest of
the body
_1 2 3 4
}:&.}. 1 2 3 4 NB. remove the head, remove the tail, and then sew the
head back on
1 2 3
|:&.}. i.4 3 NB. remove the head, transpose the body, and then
reattach the head
1 2 3
3 6 9
4 7 10
5 8 11
|.&., i.2 3 NB. ravel, reverse, and then unravel
5 4 3
2 1 0
To make this functionality available to users, I suggest using .: for
'assign under', by analogy to :. and ::. Then:
u&.:(v .: vu) y ←→ vu y;u v y.
x u&.:(v .: vu) y ←→ vu x;y;(v x) u v y
The reason that vu is only applied monadically is to allow for the
expected identity:
u&.:(m&(v .: vu)) y ←→ m vu y;u v y
Thoughts?
-E
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