The APL Orchard

B. Wilson

05:17

@Adám Cheers. Is this issue tracker publicly accessible? I'm not finding anything relevant in Dyalog's GitHub organization.

Adám

@B.Wilson No, internal, but I'll update you here when there's a development.

B. Wilson

Roger.

B. Wilson

06:07

⎕←⌈/⍬

Hrm. is the bot asleep?

Adám

⎕←'test'

Strange, it works here

B. Wilson

Hrm. TryAPL displays as away here but present in that other chat.

B. Wilson

06:22

@TryAPL ⎕←'Wake up. You are being watched.'

B. Wilson

06:36

Negative indices into an array. Since Take and Drop both allow negative "indices", it seems natural that Index, Pick, and Bracket Indexing would allow the same.

Has this been explicitly rejected? Or is it an ongoing discussion?

B. Wilson

07:00

Hrm. So the prototype for 0↑A seems to come from ⊃A. E.g. (0⍴⊂0 0 0)≡0↑(1 2 3) (1 2).

I guess that's reasonable. There's really no algebraically sound answer for what a prototypical element of a nested array is.

Adám

07:14

@B.Wilson Many times. What happens if ⎕IO←0?

@B.Wilson It isn't so much that, as what happens with F¨empty. We need some prototypical data to derive the corresponding result. E.g. {2↑¨2 2⍴⍵}¨0⍴⊂'a'1'b'

Surely, the result must be a 2-by-2 matrix of 2-element vectors, all but the top-right one being character, with that one being numeric.

B. Wilson

@Adám I'd intuit that negative indices are unaffected by ⎕IO, since we want (¯1⌷A)≡¯1↑A, but I see your point.

Adám

07:32

I'd make correcting for ⎕IO so much more involved.

B. Wilson

@Adám Sure, but you could just as well derive that prototypical data from any other element of A.

Adám

@B.Wilson Let me guess, you actually just want the last element?

@B.Wilson What do you mean by "any other". There aren't any other, let alone any at all.

B. Wilson

The prototype of 0↑(1 2 3)'abc' is numeric, not character. Just observing how ↑ chooses to generate a prototype.

Adám

Think of it as a progressive peeling away trailing elements, since length and shape goes from the front. The last element to disappear is the first one.

B. Wilson

I definitely agree that it's a natural-feeling choice! However, AFAICT, there's no mathematical/mechanical reason to choose the first. It seems just as "mathematically consistent" to make (0⍴⊂' ')≡0↑(1 2 3)'abc'.

Adám

07:39

I guess. Indeed, for "over-taking", the last element might make more sense,: 3↑1 'a' → 1 'a' ' '. But as would cycling: 4↑1 'a' → 1 'a' 0 ' '.

B. Wilson

Exactly. The peeling analogy implicitly chooses a sequence of left-arguments. Certainly a common choice, but if there were a problem domain where you only cared about even-indexed elements, then the 2nd element might be a more natural prototype base in that case.

Adám

Even worse/more compelling:

      4↑3 2⍴'Name' 'Age' 'Ann' 31 'Bob' 27
┌────┬────┐
│Name│Age │
├────┼────┤
│Ann │31  │
├────┼────┤
│Bob │27  │
├────┼────┤
│    │    │
└────┴────┘

Surely, that bottom right corner should say 0

B. Wilson

Ah! Yes! Massively more compelling.

B. Wilson

09:11

Function definition contents in aplf file might be different from running definition in session (shown by ⎕VR), which might be different than the contents in the Editor, which need to be FIXed.

Adám

@B.Wilson What are you trying to say?

I mean, yes, it is true, but so?

B. Wilson

Just me talking out loud, mostly, as I explore.

Adám

:-)

⎕VR (although you should get used to using ⎕ATX) should mostly correspond to what you see in the editor.

B. Wilson

I can shut up if it's too spammy. Apologies.

↑Wifi temporarily cut out just before I sent that.

Adám

No, it is fine. I was just wondering if you were complaining about or asking something.

B. Wilson

09:20

@Adám Yeah as long as you've FIXed editor changes, they should be the same, right?

Cool! ⎕ATX looks really nice. I love how much tooling Dyalog has available for introspection.

Adám

@B.Wilson ⎕VR includes line numbers and ∇s, and normalises formatting.

B. Wilson

Yeah. It looks like 6*⎕ATX gives a vector of lines, even including comment lines and stuff in an apl* file external to the actual definition.

Adám

Compare:

      2⎕FIX'    foo ← {' '1.0e3 × ⍵  ⍵  ⍵}'
      62⎕ATX'foo'
┌───────────┬────────────────┐
│    foo ← {│1.0e3 × ⍵  ⍵  ⍵}│
└───────────┴────────────────┘
      ⎕NR'foo'
┌──────┬────────────────┐
│ foo←{│     1000×⍵ ⍵ ⍵}│
└──────┴────────────────┘
      ⎕VR'foo'
     ∇ foo←{
[1]        1000×⍵ ⍵ ⍵}
     ∇

B. Wilson

Ah! I see what you mean. Is the extent of normalization limited to constant folding and whitespace munging?

Adám

Those are the only ones I can think of.

B. Wilson

09:35

Cheers.

Adám