[Openmcl-devel] DEFSTRUCT and :INCLUDE

Tim Bradshaw tfb at tfeb.org
Wed Oct 14 08:55:53 UTC 2009


On 13 Oct 2009, at 16:43, Daniel Weinreb wrote:

> There are two separate questions here: what is the
> definition of the Common Lisp language, and what
> should CCL do?
>
> Regarding the former, I think I can say pretty reliably
> that during the design of CL, nobody thought about
> this.  So the spec is not written in such a way as to
> give unambiguous guidance about what these forms
> ought to do.

I agree with this.  However I think it's clear that, if they had  
thought about it, they would not have mandated the kind of obscure  
accidental name-capture that CCL does (and which other implementations  
may well do as well), if only because it would give the hygienic macro  
people cause to poke fun at CL.

I think one could argue from this text: "The slot default init forms  
are evaluated in the lexical environment in which the defstruct form  
itself appears and in the dynamic environment in which the call to the  
constructor function appears." that CCL (and some other  
implementations) are wrong.  However this is not clear enough since  
"the defstruct form" needs to be something like "the defstruct form  
which introduces the init form".

>
> In a case like that, the CCL maintainers have to
> give some consideration to the question of
> whether introducing a new behavior that is
> not consonant with other CL implementations
> may be a drawback of a proposed change (to
> be weighed among all the pros and cons).

I also agree with this.  However I suspect strongly that the number of  
instances of code which defines structures which include other  
structures, which have init forms which capture names like this, *and*  
where the included structure was defined in a non-empty lexical  
environment is zero.  So the change would not affect any code.

On the other hand the same argument says that this is fixing a problem  
which never affects any code, so why do it?

I guess my original message was just so it would appear in an archive  
somewhere, I was not expecting a fix.  What I probably should have  
done is file a very low priority bug or something, but I don't know  
how (no, don't tell me!).

--tim




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