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

[Dr . Jürgen Sauermann]

    Hi,
      
      ⍸ added in SVN 1368.
      
      Best Regards,
      Jürgen

On 11/27/20 2:26 PM, Russtopia wrote:

Aha, I suspected as much, but being so new to the language I thought I would ask here to be sure.

Thank you so much for your work on GNU APL. I still don't know exactly how or where I'll use APL, but I am enjoying how it directs one to think about problem-solving.

-Russ

On Fri, 27 Nov 2020 at 05:42, 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