Peter Seibel <pe
...@javamonkey.com> writes:
> I don't see anything that that suggests it fits into any part of the
> meta object protocol though I can imagine you'd need a function like
> this to implement the initialization argument validity checking
> described in Sec 7.1.2. Is that it?
> Or is it a historical artifact of some earlier Lisp that was kept
> around for compatibility?
I doubt "of some earlier Lisp" is correct. It might be an artifact of
some later Lisp kept around for compatibility. (Read on to see how that
might be possible.)
> Or something else?
Always possible.
Btw, not that everyone agrees with me on this, but I have a personal
distaste for this approach to learning the language of trying to learn
how each operator is to be used. When one sees a function they don't
see a use for, I think the right thing is not to try to invent uses
for it, it's just to file some superficial info about the fact that it
might be used later and then to not use it. The reason for this is that
people often talk about the language as complex because of how many things
it has in it, but not all of those things are day-to-day things. Some are
extraordinarily specialized and just not needed for everyone.
One thing to know about CLOS in general is that it was presented as a
whole to the committee for acceptance, but it was a 3-chapter text.
We accepted the first chapter, and not the other two, if I recall. (Or
maybe it was the first two but not the third.) In any case, it was
approximately the non-MOP part. But it was easier and design-wise
safer in that historical context just to take an intact chapter than
to do surgery to remove parts of it that were really not needed
without the other 2. (You should know that while I did substantial
surgery on the text of the rest of the document, a great deal of the
CLOS stuff is taken verbatim from the original proposal and I was
forbidden from doing even superficial modification because so much
blood was already spilt among the CLOS committee getting the necessary
compromises for agreement that no one wanted to risk additional blood
spilt again in a redundant process of integration into the spec as a
whole.) So it's extremely probable that there are several things in
this section whose purpose is not apparent without considering the MOP
substrate as part of the system, which it was assumed would come
later, and which, in effect, did come later since the MOP (or, as I
like to say, punning badly on the book title, "a MOP" if not "the
MOP", since there might be some variation among MOPs and the definite
article might be ill-used here) Certainly there are other pieces, like
the METHOD-COMBINATION class, that are like this.
