R.E. Boss wrote:
| log10 &.(".@>)dj
Wow, thanks! It's probably obvious and second-nature to most people
here, but I think that the use of "under" was quite clever! (I'm just
not yet at the point where that primitive is "under my belt". That's
why I would not have thought of using it.)
Just to confirm that I'm understanding the necessity for "atop": because
there were TWO verb actions that had to be "undone" at the end, "atop"
was used to create a single "compound" verb that could be used by
"under". Right?? I also intuited that the obverse ought to reverse the
order of the "atop" verbs: "b. _1" showed that to be the case.
Curiosity question: can more than two verbs be combined via "atop" for
use by "under"? How would that look in terms of parenthesization?
a...@b@c...@d or a@(b@(c...@d)) or ((a...@b)@c)@d or something else entirely?
I'm sure there's some APL history here: why is this primitive called
"under"? The definition tells what it does, but what's it good for?
That is, how (and for what purposes) is "under" used practically?
Besides you all, who in the world would ever think of such an inversion
of verbs? I mean, it's sort of a "do it" and then "undo it" again after
a key verb. Is that its main purpose? It's just plain very clever and
"cool"! Thanks!
Harvey
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