Re: Support for 'where' primitive '⍸' ?

[Jay Foad]

Dyalog's documentation for Where (monadic ⍸) is here:
http://help.dyalog.com/18.0/#Language/Primitive%20Functions/Where.htm
It was implemented long after Mastering Dyalog APL was written.

Re: monadic ⍳ with vector arguments, I believe Dyalog got this from
the original NARS: see https://aplwiki.com/wiki/NARS: "Additionally,
Index Generator was extended to allow a vector argument".

Jay.

On Fri, 27 Nov 2020 at 13:42, Dr. Jürgen Sauermann
<mail@jürgen-sauermann.de> wrote:
>
> Hi Russ,
>
> welcome to APL. And welcome to bug-apl@gnu.org. The latter is a moderated 
> list, so please subscribe to
> it because otherwise each of your emails will require (manual) approval by 
> myself.
>
> Back to your question, ⍸ is definitely not a standard APL primitive. My only 
> source of information about Dyalog APL,
> the book with the title Mastering Dyalog APL - A Complete Introduction to 
> Dyalog APL, seems not to mention it
> either.
>
> I am somewhat reluctant when it comes to introducing non-standard APL 
> functions into GNU APL. In my
> opinion, which is certainly arguable, non-standard extensions of APL may lure 
> APL programmers into
> writing non-standard APL programs, which in turen undermines and even 
> contradicts the principles of
> free software.
>
> For a non-standard extension to make it into APL, the extension has to 
> smoothly integrate into APL. One
> of the rare examples where this was the case was monadic ⍳ with vector 
> arguments adopted from
> Dyalog APL. That extension was sort of filling a rather arbitrary gap in 
> standard APL, making APL
> more consistent than it was before.
>
> Some other extension in Dyalog did not make it into GNU APL because IMHO the 
> additional benefit that
> they provided was not worth the incompatibility that every non-standard 
> extension unavoidably creates.
>
> I cannot judge to which kind of extensions ⍸ belongs since I do not know what 
> it actually does. I will consider
> any opinions posted on bug-apl@gnu.org, though.
>
> Best Regards,
> Jürgen
>
>
>
> On 11/26/20 11:15 PM, Russtopia wrote:
>
> Hi, newbie to APL so my sincere apologies in advance if this is incorrect, an 
> FAQ, or by design (intentionally not implemented).
>
> Dyalog APL appears to support monadic ⍸ (underscore-iota) primitive as a 
> 'where' function, eg.
>
>     b ← 0 0 1 1 0
>     ⍸b
> 3 4
>
> ..whereas GNU APL considers the ⍸ as an invalid symbol (SYNTAX ERROR)
>
> Equivalent seems to be
>     b / ⍳⍴ b
> 3 4
>
> .. just wondering if this is a Dyalog non-standard and if GNU APL plans to 
> implement it.
>
> Thanks,
> -Russ
>
>