Re: ⍬ bug?

[Dr . Jürgen Sauermann]

Hi David,

not sure either if this is a bug. The APL standard has quite a specification gap
when it comes to binding strength. In GNU APL, the binding between values
(aka strand notation) is stronger than the binding between values and functions.

For example:

      V←⍳0

∇Z←F
 Z←⍳0
∇

Both V and F result in the same value ⍬:

      V≡F
1

However, they are parsed differently:

      2 V 3⊃a
3

      2 F 3⊃a
 2    99

In the first case: 2 V 3⊃a the value V binds strongly to 2 and 3 so that value (2 V 3)
 becomes the left argument of ⊃. In the second case:  2 F 3 the value 3 binds
stronger to ⊃ than to F so that first  is evaluated 3⊃a and then the result of ⊃ is
tied to the F and 2.

In GNU APL ⍬ is a niladic function, so it behaves like F above.

This behaviour could be changed, but I hesitate to do that since it might break
existing code. The impact of such a change would not only affect ⍬ but all niladic
functions.

Best Regards,
Jürgen Sauermann

On 12/24/19 2:49 AM, David Tran wrote:

Ooops, missing something on my examples, correction:  ( missing ⊂ on ⍳3 )

a ← 'abc'(⊂⍳3)99

the 3 examples are the same:

2(⍳0)3⊃a

2⍬3⊃a

(2⍬3)⊃a

On Mon, Dec 23, 2019 at 7:20 PM David Tran <address@hidden> wrote:

Hi,

Not sure this is a bug or not, for me, (⍳0) ≡ ⍬, so it seems that both can be replaced each other; consider below example:

a←'abc'(⍳3)99

2(⍳0)3⊃a ⍝ ≡ 3

2⍬3⊃a ⍝ ≡ 2 ⍬ 99

(2⍬3)⊃a ⍝ ≡ 3

Doesn't the second example should return 3 as first example, without the need parentheses as third example?

(btw. my version is build from SVN around Oct )

Thanks,

Dave