Re: APL2 Compatibility

[Dr . Jürgen Sauermann]

    Hi Adam,
    
    thanks, see below.
    
    Best Regards,
    Jürgen
    
    
    On 11/23/20 11:07 PM, Adám Brudzewsky wrote:

For the sake of compatibility with IBM APL2

Speaking of which, what is GNU APL's official policy?

    GNU APL's general policy regarding standards and the like is to
    consider,
    (in that order):
    
    1. the IBM APL2 language reference manual,
    2. the IBM APL2 implementation (PC demo version, can't aford the
    commercial version),
    3. the ISO standard,
    4. other APL implementations and suggestions from bug-apl@gnu.org.
    
    Sometimes, however, this can have undesirable consequences and then
    some sort of common sense is applied to change the order.

I noticed that the info manual (https://www.gnu.org/software/apl/apl.html#APL-symbols-that-can-be-functions-or-operators) is factually wrong about APL2, claiming that:

the ambiguity related to / ⌿ \ and ⍀ is not resolved by these rules.

    I see. That statement is probably a left-over from the early days of
    GNU APL. When I started
    with GNU APL, all I had was some vague recollection of APL1 from the
    1970s (my first APL
    computer was an IBM 5110 desktop, a precursor of the IBM PC). At
    that time functions were
    functions and values were values. At some later time, triggered by
    the ⍤-operator (which was
    not implemented in IBM APL2 but defined in ISO), I changed to the
    APL2 way of handling /
    and \.
    
    I have updated the documentation, SVN 1363.

The APL2 language reference does in fact make it perfectly clear how / and friends are treated, namely as operators. Always. Note:

And then:

Note that this makes APL2 ISO non-compliant. Indeed, here, GNU APL follows Dyalog and NARS2000:

      1 2 3/¨'ABC'
 A BB CCC

While APL2 and APLX give:

      1 2 3/¨'ABC'
 AAAAAA BBBBBB CCCCCC

This is because 1 2 3/ is a derived monadic function and ¨ maps the entire function to each letter.

    I believe older GNU APL versions would have given the APL2/APL X
    results, while newer versions
    give the other result. This is one of the examples where the general
    GNU APL policy is not being
    followed. If an incompatibility with APL2 exists long enough with no
    complaints from the users,
    then I believe backward compatibility with GNU APL is more important
    than compatibility with IBM
    APL2.

On Mon, Nov 23, 2020 at 9:21 PM Dr. Jürgen Sauermann <mail@jürgen-sauermann.de> wrote:

Hi Kacper, Adam,

thanks. For the sake of compatibility with IBM APL2 I have changed ⎕UCS so that
it accepts float and complex numbers that are near to integers.  My initial thinking was
that e.g. ⎕UCS of a complex number is most likely a programming mistake so
that a DOMAIN ERROR would be more helpful than being a burden. But APL2
compatibility is an even stronger argument in this case.

I have also adjusted the integer domain which is now -$80 ... $7FFFFFFF
so that no conflicts with signed bytes from ⎕FIO should arise.

SVN 1362.

Best Regards,
Jürgen

On 11/22/20 11:11 PM, Kacper Gutowski wrote:

On Sun, Nov 22, 2020 at 03:19:19PM +0100, Dr. Jürgen Sauermann wrote:

Floating point and complex numbers are not allowed as to avoid interference with ⎕CT (i.e. how should rounding be performed?).

I share your sentiment regarding the upper bound of the ⎕UCS domain, but throwing a domain error on ⎕UCS1E2 looks like a bug to me too.  1E2 is clearly an integer regardless of the implementation details, and I would be surprised if APL2 didn't accept it.  I would expect rounding to be the same as in all the other places that require near-integers, like array indices.

The negative ones are also a bit weird.  I wasn't aware of their existence, and they seem to work in surprising ways when passed to various variants of ⎕CR.

-k