Sure, but in a left to right fold like X U F..V Y, X should be the
control, and currently, it's not being treated that way in the context
of V.
Thanks,
--
Raul
On Tue, Feb 23, 2021 at 11:22 PM Henry Rich <henryhr...@gmail.com> wrote:
>
> IMO the data/control concept is decisive, overriding any esthetics about
> where x should go.
>
> I say eether, you say eyether.
>
> Henry Rich
>
> On 2/23/2021 9:13 PM, Raul Miller wrote:
> > On Tue, Feb 23, 2021 at 3:37 PM Hauke Rehr <hauke.r...@uni-jena.de> wrote:
> >> Folds are a variation on /
> >> There’s not much more to it.
> > My thinking is this:
> >
> > For dyadic uses of folds, the left argument to the verb derived by
> > fold should be the initial value for the sequence.
> >
> > Meanwhile, there's two kinds of folds. Right to left folds and left to
> > right folds.
> >
> > Right to left folds (F.: is like / and F:: is like /\.). For those
> > folds, it makes sense that the initial value be the right hand
> > argument to the first invocation of the fold's v argument.
> >
> > Left to right folds (F.. and F:.) do not have corresponding primitive
> > adverb. For these folds, it makes sense that the initial value be the
> > left hand argument to the first invocation of the fold's v argument.
> >
> > In other words:
> >
> > V=: {{x+y [ echo x,y}}
> > 7 ]F.:V 1 2 3 4
> > 4 7
> > 3 11
> > 2 14
> > 1 16
> > 17
> >
> > This is perfect. 7 is the initial value, and you get the same result
> > from this expression:
> > 1 V 2 V 3 V 4 V 7
> > 4 7
> > 3 11
> > 2 14
> > 1 16
> > 17
> >
> > It's just like inserting V between each of the items in the list, and
> > tacking 7 on as the initial value.
> >
> > Or, to emphasize the right to left nature of that expression, we could
> > put in the implied parenthesis:
> > 1 V(2 V(3 V(4 V 7)))
> > 4 7
> > 3 11
> > 2 14
> > 1 16
> > 17
> >
> > -------------
> >
> > For the left to right folds, we do basically the same thing, but we
> > would have to use parentheses to force left to right evaluation. In
> > other words, we should expect that
> >
> > 7 ]F..V 1 2 3 4
> > works like this:
> > (((7 V 1)V 2)V 3)V 4
> > 7 1
> > 8 2
> > 10 3
> > 13 4
> > 17
> >
> > And, in my earlier tests today, I thought I was getting that result.
> > But I see now that I am not.
> >
> > 7]F..V 1 2 3 4
> > 1 7
> > 2 8
> > 3 10
> > 4 13
> > 17
> >
> > Anyways, for the F.. and F:. verbs, I think it does make sense to
> > change the fold implementation, so that the 'initial' or 'previous'
> > value appears on the left.
> >
> > And, looking back on what Sergy wrote, it looks like I was reading him
> > wrong.
> >
> > Thanks,
> >
>
>
> --
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