[Openmcl-devel] (setf (find-class ...) ...) problem

[Cyrus Harmon]

Gary,

Thanks for the thoughtful explanation. Explicitly deftype'ing the  
class first sounds reasonable to me. I've asked the cxml-stp  
developers for their opinion as well.

thanks again,

cyrus

On Nov 30, 2008, at 6:12 PM, Gary Byers wrote:

>
>
> On Sun, 30 Nov 2008, Cyrus Harmon wrote:
>
>> I'm trying to use david lichteblau's cxml-stp with ccl and am getting
>> errors about undefined types. It seems that ccl doesn't like the
>> following:
>>
>> (setf (find-class 'document-type) (find-class 'cxml-stp:document- 
>> type))
>>
>
> I assume that you mean something like:
>
> (defclass fruit () ())
>
> (defclass orange (fruit) ())
>
> (setf (find-class 'tangerine) (find-class 'fruit))
>
> (typep (make-instance 'orange) 'tangerine) complains that TANGERINE
> isn't a valid type-specifier.
>
> My first reaction was to think that that was a bug, but after looking
> at the spec for a while I haven't yet found anything that confirms
> that and have found at least one passage that (weakly) contradicts  
> that intuition, but it's a bit unclear.
>
> The second paragraph of CLHS 4.3.7 says that "the PROPER name of
> every class is a valid type specifier.", then discusses the use
> of class objects as type specifiers and notes TYPE-OF's behavior
> wrt instances of properly and improperly-named classes.
>
> The next paragraph says "Because the names of classes and class
> objects are type specifiers, they can be used in special form THE and
> in type declarations."  I think that the clearest reading of that is
> something like "Based on what was established in the preceding
> paragraph, the PROPER names of classes ... can be used in THE forms
> and as type specifiers."  I'd feel better about making that claim
> if the language in the third paragraph was a little stronger, but I
> find it hard to parse the "because" qualifier as referring to anything
> but what's established in the preceding paragraph.
>
> I couldn't find anything else in the spec that was any clearer; the
> other things that I found referred to things like "symbols naming
> classes defined by DEFCLASS" and their relation to the type system.
> (I didn't find anything analogous discussing "symbols established
> as class names via (SETF FIND-CLASS).")
>
> I don't see anything in the spec that says that improper class names
> -can't- be treated as type specifiers, and it's hard to imagine that
> anyone's code would break if CCL's (SETF FIND-CLASS) stopped checking
> for proper-namedness in this case, though it's not quite impossible
> imagine that.  I'm also perfectly willing to believe that there's
> something else in the spec that's more definitive and that contradicts
> the interpretation above, but in the absence of that I have to  
> conclude
> that code that assumes that (SETF (FIND-CLASS a) c)  S into a valid
> type specifier is incorrect (even though it likely "works" in most/all
> other implementations.)
>
> I think that there actaully are reasons for the spec's (seeming)  
> insistence
> on only considering properly-named classes to be type specifiers (and
> that those reasons probably have to do with the compilation model.)   
> I'm
> not sure that those reasons are fully developed, but I don't think  
> that
> the spec's distinctions between proper and improper class names are  
> arbitrary and accidental, either.
>
>
>
>
> If we all strongly believed that (SETF FIND-CLASS) only made S into
> a type specifier if S was the class name of C, then a portable way
> of doing this would be something like:
>
> (setf (find-class s) c)
> (deftype s () 'c)       ; whatever the "proper name" of C is
>
> CCL actually errs in the expansion of DEFTYPE, because S names a class
> (even though it doesn't properly name it and even though it's  
> therefore
> not a type-specifier; it'd be more consistent if the expansion of  
> DEFTYPE
> did the same kind of check for proper-namedness that (SETF FIND- 
> CLASS) does.
>
> It -does- work to do the DEFTYPE first:
>
> (deftype tangerine () 'orange)
> (setf (find-class 'tangerine) (find-class 'orange))
>
> I'm not entirely comfortable in saying that I think that CCL's "right"
> about this (at least in trying to adhere to the letter of the spec)  
> and
> that other implementations are all wrong.  At the moment, let's just  
> say
> that I'm not entirely comfortable (though I think that I'd be a little
> closer to comfort if CCL was more consistent, e.g., if DEFTYPE's  
> expansion
> only rejected attempts to redefine class-names that the implementation
> considered to be type specifiers.)
>
>
>
>
>
>
>
>
>
>> a similar problem was discussed a while back where this problem arose
>> with GSharp, but I'm not sure what the resolution was. Any  
>> suggestions?
>>
>> thanks,
>>
>> Cyrus
>>
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