Re: [Sbcl-devel] Fascist STYLE-WARNINGs in SBCL

[Christophe R. <cs...@ca...>]

Marco Antoniotti <ma...@cs...> writes:

> Always in the specific case, since there is code in SBCL to test for
> the second argument to PRINT-OBJECT, such code should at a minimum
> test that the second argument is "fine".  STREAM is fine.  Testing for
> abuses on the identity of the object (i.e., tests like (eq s
> *standard-output*) ) are too much to test for, but it is those those
> that are the target of the caveat in the spec.  Not the STREAM
> declaration.

It is not "fine" in any circumstances, but for reasons that are perhaps
not directly spec-related.  Your specialization might be OK from the
point of view of the spec -- I do not want to debate that -- but for a
change there is a non-spec reason for warning the user, regarding the
precomputation of methods in exceptional situations.  Specifically,
while CLOS is in general a lazy system, in that it computes effective
methods on demand, there is one area where that doesn't work so well,
and that is the reporting of errors ("exceptional situations") to the
user: if the system is nearly out of resources, it is bad if the system
has to use resources to compile effective methods in order to print a
message to the user.

So PRINT-OBJECT is special-cased.  But that special-casing only works
when all the methods have only one dispatch argument -- i.e. when the
second is always specialized to T, and hence doesn't figure in
applicability calculations.  If it does, then the special-casing fails,
and you're on your own: the eager computation of relevant effective
methods is no longer possible.  (Well, of course it's possible with even
more heroic effort; I look forward to a world where such heroic effort
can be had at the beck-and-call of an angry e-mail)

> In other words, I really believe that SBCL should be much more lenient
> in many cases where the spec interpretation is not so clear cut.

Why do you actually want to specialize on STREAM?  The standardized
methods don't, after all.  All it can do is make your printing slower
and the overall system more fragile.

Cheers,

Christophe