Whoops. Looks like I got here too late.
Well done!
Louis
> On 28 Apr 2016, at 00:29, Louis de Forcrand <ol...@bluewin.ch> wrote:
>
> The three-item form is used if the associated function is ambivalent (applied
> to the P-cells of ⍵ if monadic, applied to corresponding Q-cells of ⍺ and
> R-cells of ⍵ if dyadic). I don't believe it is possible to define ambivalent
> functions in ISO APL however, so it is kind of redundant. It is probably left
> over from Sharp APL.
>
> As to the negative rank, I believe that it is an obvious flaw in the
> standard. Being able to apply a function to the items of the argument is
> incredibly useful. Of course this is achievable like so:
> {⍺ (f ⍤ (¯1+≢⍴⍺⍵)) ⍵} ⍝ without ⍺ for the monadic form
> Now that I've checked, I'm pretty sure that GNU APL does support rank
> (negative or not), but not with all primitives. Try it out with ⊖ or +⌿ on a
> rank-3 or above array, and then with ]BOXING and ⊂ on the same array… looks
> like a bug to me.
>
> The rank operator isn't easy to grasp, and it's surely harder to implement.
>
> Good luck,
> Louis
>
>> On 27 Apr 2016, at 13:14, Jay Foad <jay.f...@gmail.com
>> <mailto:jay.f...@gmail.com>> wrote:
>>
>> Incidentally, it works like this in Dyalog and NARS2000 too, though
>> the Dyalog documentation doesn't mention the 3-item form.
>>
>> Jay.
>>
>> On 27 April 2016 at 09:02, Jay Foad <jay.f...@gmail.com
>> <mailto:jay.f...@gmail.com>> wrote:
>>> Given g ← f⍤P Q R:
>>> P is the monadic rank
>>> Q is the left rank
>>> R is the right rank
>>>
>>> So:
>>> g Y applies g to the P-cells of Y
>>> X g Y applies g to the Q-cells of X and the R-cells of Y
>>>
>>> The ⌽3⍴⌽y1 stuff is just a too-cute way of saying that you can specify
>>> fewer than 3 values in the right operand, and:
>>> R is shorthand for R R R
>>> Q R is shorthand for R Q R
>>
>
