[pro] AMOP question: When and where is slot-value-using-class called?

[Scott L. Burson]

That reminds me of the time I did

  (trace format)

That _did_ crash the LispM, very, very hard.

-- Scott


On Sat, Aug 2, 2014 at 8:52 PM, Steve Haflich <shaflich at gmail.com> wrote:

> OK, now I'm sitting in front of the front end of a computer rather than
> the back end of a smelly wet large long-haired dog.
>
> The restriction on "portable programs" extending (redefining, whatever)
> MOP functions is here:
>
>
> http://franz.com/support/documentation/current/doc/mop/concepts.html#portable
>
> The motivation for this particular restriction is twofold.
>
> First, the CL language implementation as well as the MOP itself may depend
> upon the MOP itself.  The intention is that the language and MOP can use
> CLOS and even the MOP in their own implementation, and if they do, and use
> only "specified" classes or classes specified on class (and operator) names
> in private packages or otherwise unexported and unknown to properly-written
> portable programs, those programs won't break the implementation or affect
> the efficiency of its implementation.  This is no different than the ANS
> prohibition against redefining cons to take its arguments in reverse order,
> expecting that if the portable user application code was written against
> this specification, the result would be harmless.  But global definitions
> Lisp worlds are indeed global (*).
>
> The second reason is less obvious.  The implementation of ANS CL, CLOS,
> and the MOP obviously all depend upon themselves.  Thus their
> implementations are metacircular and need protection.  Furthermore, the
> full MOP protocol even where not metaciculr is expensive.  If it must be
> obeyed for "specified" operators on objects of "specified" classes,
> execution efficiency may be unacceptable.  The CLOS and MOP subcommittee of
> X3J13 IMO did an exquisite job making it possible to implement these
> subspecifications into a usable "industrial-strength language."
>
> The CLOS subcommittee recommended that CLOS, but not MOP, be accepted into
> the standard, because the MOP had never yet been fully implemented, and was
> not yet ready for standardization.  That is exactly what we (X3J13) voted.
>
> (*) Back around 1986 just before I intended to reboot my Lisp Machine
> anyway I redefining car and cdr with the other's definition.  I expected an
> immediate flaming crash, however, the machine kept running just fine.  This
> is because the implementation had already compiled all the important
> functions that called csr and cdr, and those calls obviously would be
> inlined, making my redefinitions ineffectual.  I'm sure if I had searched
> for some code that passed #'car or #'cdr as a :key argument to some other
> function, I might have provoked some failure, but otherwise the machine and
> OS didn't care.
>
>
>
> On Sat, Aug 2, 2014 at 2:59 PM, Kenneth Tilton <ken at tiltontec.com> wrote:
>
>> Note that the MOP is not part of the spec. They explicitly punted on
>> making it so. Ergo, you are likely fishing in unspecified waters, or dog
>> parks as the case may be.
>>
>> Note also that no one has asked you what problem you are trying to solve.
>>
>> Until now.
>>
>> hth, hk
>>
>>
>> On Sat, Aug 2, 2014 at 5:26 PM, Attila Lendvai <attila.lendvai at gmail.com>
>> wrote:
>>
>>> > I got different results in pretty much each CL implementation on the
>>> > tracing of calls to slot-value-using-class.
>>>
>>> make sure you're not using CL:TRACE for this because it may not work
>>> on SVUC due to various optimizations.
>>>
>>> --
>>> • attila lendvai
>>> • PGP: 963F 5D5F 45C7 DFCD 0A39
>>> --
>>> “A true intellectual is a man who, after reading a book and being
>>> convinced by its arguments, will shoot someone or, more likely, order
>>> someone shot.”
>>>         — John McCarthy
>>>
>>> _______________________________________________
>>> pro mailing list
>>> pro at common-lisp.net
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>>>
>>
>>
>>
>> --
>> Kenneth Tilton
>> Fort Lauderdale, FL
>> http://tiltontec.com
>>  "In a class by itself." *-Macworld*
>>
>>
>>
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>
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