Hi,
after investigating ⍸ I have added it to my TODO list.
Although its monadic form could be easily emulated with standard APL
primitives,
the dyadic form seems to be useful (find the interval into which a value
falls) and,
more importantly, not so easy to implement in APL.
Still wondering if monadic ⍸ B with non-boolean B has a real-life use case?
Best Regards,
Jürgen
On 11/27/20 9:34 PM, Dr. Jürgen Sauermann wrote:
Hi Jay,
thanks a lot for the pointers.
Best Regards,
Jürgen
On 11/27/20 2:48 PM, Jay Foad wrote:
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
