[armedbear-devel] eql for java objects

Erik Huelsmann ehuels at gmail.com
Sun Apr 25 18:37:32 UTC 2010

Hi all,

On Sun, Apr 25, 2010 at 7:26 PM, Alan Ruttenberg
<alanruttenberg at gmail.com> wrote:
> On Apr 25, 2010, at 6:55 AM, Tobias C. Rittweiler wrote:
>> I think that's past Alan's point which, from my understanding, is simply
>> "Java enums should be comparable by EQL." Makes perfect sense as EQL is
>> for object identity.
> Yes, and Java "objects" too.

I've read this thread, the thread on c.l.l regarding EQUAL and the
definitions of EQ and EQL. The following is my interpretation of it

1. Our Java side JavaObject class is merely a box for a Java instance
value (a pointer to a Java object, if you will)
2. The definitions of EQ and EQL talk about Objects, but I interpret
them to refer to the first meaning in [1], not to instances of lisp
3. Our JavaObjects have not been defined in the (Common) Lisp spec;
they don't adhere to the object-instantiation protocol nor are they
any of any one of the predefined built-in classes and therefore can't
be taken to be "Lisp Objects" in that sense of the word
4. From point (1) and the definitions of EQ and EQL, I concur with
Alan that "raison d'etre" of EQL should equally apply to JavaObjects
5. From ponits (2) and (3) and the discussion on #lisp and c.l.l, I
conclude that we're basically free to extend the meaning of EQL here:
the JavaObject values were not in the spec to begin with: they're not
Lisp class instances, they're not symbols, numbers nor characters

The only objection there is from both #lisp and c.l.l is that EQ, EQL
and EQUAL shouldn't start to behave unpredictably regarding defined
behaviour. For all the spec cares, we would have generated an error
when EQ-comparing 2 java objects...




[1] http://www.lispworks.com/documentation/lw51/CLHS/Body/26_glo_o.htm#object

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