Re: [Bug-apl] Defining APL functions with [ ]

[Juergen Sauermann]

Hi,

yes, the reason is this:

Sometimes you want to have (user-defined) wrapper functions around primitives, for example
to get some statistics about their use (how often called, averge size of arguments, etc).
It is pretty easy to convert a normal APL program to one using the wrappers instead of
the primitives.

That fails, however, when a primitive function or operator has an axis argument.

I also found it generally more plausible if user defined function can also have an
axis argument. For example you can define the average of a vector like this:

∇Z←Avg B
 Z←(+/B) ÷ (⍴B)
∇

But you can't normally define the average along an axis like this:

∇Z←Avg[X] B
 Z←(+/[X]B) ÷ (⍴B)[X]
∇

With GNU APL you can:

      Avg[1] 5 5⍴⍳25
11 12 13 14 15

      Avg[2] 5 5⍴⍳25
3 8 13 18 23

/// Jürgen


On 06/03/2014 04:39 AM, Elias Mårtenson wrote:

As far as I understand, it's an extension that is unique to GNU APL.

Regards,

Elias

On 3 June 2014 10:37, Blake McBride <address@hidden> wrote:

Greetings,

APL-1 did not allow functions to be defined with [ and ] in the header.  I've seen it done in GNU APL as follows:

      ∇fun[⎕]∇

    ∇

[0]   fun[x]y

[1]   x

[2]   y

    ∇

      fun[4]55

4

55

I understand what is going on, but I was looking for it in the APL-2 manuals.  I couldn't find it in any of the IBM manuals (and the spec is unreadable to me).  So, my question is, where in the IBM APL-2 Language Manual is it shown?  Any place else?

Thanks.

Blake