Re: [j-devel] Printing Java objects

[Erik H. <eh...@gm...>]

Hi Alessio,


On Sat, Jan 10, 2009 at 12:24 AM, Alessio Stalla
<ale...@gm...> wrote:
> On Fri, Jan 9, 2009 at 11:04 PM, Ville Voutilainen
> <vil...@gm...> wrote:
>> Ok, a dumb question: does this work differently between compiler/interpreter?
>> I have to say I've never really looked into how abcl does print/format, and we
>> have some reported errors there, so I cannot really give guidance wrt where
>> to look for this. Erik can most likely help you get started, if you have time
>> to look at these issues.
>
> It *seems* to me that the compiler knows nothing of printing-related
> stuff.

That's correct :-)

> However this is the first time I look at the compiler, so I
> might have missed something. Also as far as I know most objects'
> printing is implemented in Java, not in Lisp, so the compiler does not
> take part in it. I'll investigate more deeply as soon as I have a
> little time.

Well, this is partially true: most built-in classes define their
printing in Java, but all lisp-classes (including structures) define
their printing lisp-side, just as any common lisp does: by
implementing print-object. Even though I have implemented better
printing for some condition classes, it's not completely clear to me
which java methods are exactly called in which order to print object
types which don't have a print-object method. It would be nice if you
found out :-)

Most print-object methods that ABCL comes with out-of-the-box are
defined in print-object.lisp.

So, basically, there are 2 strategies: implement a lisp-side
print-object method which does what you want; it can use
*print-readably* to determine the type of output it should generate;
or maybe *print-pretty* (since Java-Object isn't readable anyway).

The other strategy would be to find out where printing of built-in
objects is defined and to change the way that works.

HTH,

Erik.