> 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 > inversionof verbs? I mean, it's sort of a "do it" and then > "undo it" again after a key verb.
http://keiapl.org/anec/#under0 ----- Original Message ----- From: "Hahn, Harvey" <[email protected]> Date: Monday, December 29, 2008 14:40 Subject: Re: [Jprogramming] How to use ": in boxed conversion? To: Programming forum <[email protected]> > 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": > becausethere 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 > parenthesizatio...@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 > inversionof 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! ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
