Would the following do?
i=: /(@,) NB. insert with initial value
pii =: /\(@,) NB. progressive insert with initial value
3 +i i. 3
6
3 + +/ i. 3
6
3 +ip i.3
3 3 4 6
This applies the same f between all elements, but adds an initial value to
start with.
Best regards
Jan-Pieter
On Fri, 2 Mar 2018, 09:38 Marshall Lochbaum, <mwlochb...@gmail.com> wrote:
> There's no clean way to do it. If the result of the first invocation of
> f has the same type as the rest of the list elements, you can do
>
> f/ _2 (}. , f0/@:{.) l
>
> and if it has a different type you can check whether the right argument
> has this type (like your "signature structure", but implicit).
>
> One of my most missed features in J is a reduce with a specified initial
> element. Thus (l f/ e) would be equivalent to (> f&.>/ (<"_1 l),<e) but
> without the very large inefficiency of boxing everything. Of course
> dyadic f/ is already taken, so it would need another symbol. With this
> feature, you could use (_2 (}. f/ f0/@:{.) l) regardless of the
> properties of f.
>
> If your initialization comes before any of the processing and doesn't
> change the arguments (so that the first function invocation f0 is
> equivalent to (f[i0) for some initializer i0), then you can use
> (f/ l [ i0/ _2{.l), that is, separate the initialization from the
> function application completely.
>
> Marshall
>
> On Fri, Mar 02, 2018 at 01:51:39PM +0530, Arnab Chakraborty wrote:
> > Hi,
> >
> > If f is a dyad, then
> >
> > f/ 2 4 5
> >
> > means
> >
> > 2 f 4 f 5
> >
> > where the rightmost occurence of f is invoked first. I am wondering if
> > there is a smart way to recognize this first invocation separately from
> the
> > rest. This will enable me to perform some initialization inside f. By
> > "smart" I mean something smarter than the followung two:
> >
> > 1) using side effect like setting a global flag.
> > 2) adding some signature structure to the output of f (eg, 'inited';
> > result),
> > and then checking the absence of this signature.
> >
> > Thanks.
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