Re: [Bug-apl] Monadic form of ↓

[Louis de Forcrand]

Since the subject has been brought up, how about using it as the analog of first (monadic take), but instead unboxing the last element of an array in ravel order?

I don’t think this can generally be done on an array X in a more concise way than 

first reverse ravel X

or

(shape X) pick X

which I suppose are both slower than a primitive could be.

This might be considered trivial as well though.

Just a suggestion!

Louis

On 10 Oct 2017, at 18:46, Juergen Sauermann <address@hidden> wrote:

Hi Elias,

I believe ↓ for 1↓ is too trivial to be useful.

Unoccupied variants of APL primitives (like monadic ↓ or monadic =) are
a very scarce resource that we should not use for trivial things.

/// Jürgen

On 10/09/2017 11:06 AM, Elias Mårtenson wrote:

I was thinking about the usefulness of a monadic ↓ in terms of the new regexp feature. In the current version, when using subexpressions, the return value is always 1+the number of subexpressions, where the first one is always the full matched string. Monadic ↓ would be a neat way of dropping that part.

In any case, my point is that monadic ↓ should do something useful. I guess split is one such useful thing.

In GNU APL, I'd use ⊂⍤1 to achieve Split. Is that the most efficient way?

Regards,

Elias

On 9 October 2017 at 16:58, Jay Foad <address@hidden> wrote:

On 9 October 2017 at 04:56, Elias Mårtenson <address@hidden> wrote:

Currently, monadic ↑ acts as if it was called dyadically with 1 as its left argument,

That's not quite true:

      ⍴⍴1↑'ABC'

1

      ⍴⍴↑'ABC'

0

while monadic ↓ raises a VALENCE ERROR. In almost every single case where I have used ↓, it has been in the form 1↓X. Is there a reason why the monadic form is not allowed?

FYI in Dyalog APL monadic ↓ is Split:

      ↓3 3⍴⎕A

┌───┬───┬───┐

│ABC│DEF│GHI│

└───┴───┴───┘

I believe this came from STSC's NARS.

Jay.