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