[R6RS] non-opaque record equality

[Matthew Flatt]

Can we put this on the agenda, too?

Although I read the hyperspec earlier, I didn't know that Common Lisp
has the notion of opacity and non-opacity for structures. If someone
can point me to the right place to read, I can become prepared for the
meeting.

Thanks,
Matthew

At Sat, 25 Feb 2006 12:10:49 +0100, Michael Sperber wrote:
> 
> Matthew Flatt <mflatt at cs.utah.edu> writes:
> 
> > Would it make sense for two records could be `equal?' when 
> >
> >  1. they are instances of the same *non-opaque* record type, and 
> >
> >  2. their corresponding field values are all `equal?'
> >
> > ? This change seems consistent with the SRFI's reflection support on
> > non-opaque records.
> >
> > I have no strong opinion, but I thought I'd bring it up for a couple of
> > reasons: extending `equal?' this way has been convenient in MzScheme,
> > and I didn't see any discussion of this possibility in the R6RS or SRFI
> > email archives (but there was a lot of discussion specifically about
> > equality, and I could easily have overlooked specifics thoughts on
> > opacity).
> 
> I disagree pretty strongly, after having worked with Common Lisp's
> EQUALP (which does essentially the same thing) in a project.  It sure
> feels convenient for a while, but there's almost always a bad
> awakening.  There was a discussion on this that's archived here:
> 
> https://r6rs.scheming.org/node/98
> 
> I wrote a longer position post here:
> 
> https://r6rs.scheming.org/node/98#comment-743
> 
> The Common Lisp issue referenced in the post and in the SRFI has even
> more.
> 
> -- 
> Cheers =8-} Mike
> Friede, Völkerverständigung und überhaupt blabla
> 
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