[r6rs-discuss] Re: [Formal] eq?/eqv? misbehave around NaNs

From: Alan Watson <alan>
Date: Fri Nov 24 16:56:39 2006

Marcin 'Qrczak' Kowalczyk wrote:
> It doesn't matter if the functions are non-standard. If the values are
> treated differently by any function except eq? and functions derived
> from eq?, they must definitely not be eqv?.

No. Consider an implementation has multiple versions of, say, symbols,
arranges from them to be eq? and eqv?, and also provides a non-standard
means to distinguish them. Symbols with the same spelling have to be
eq?, but these symbols are indeed "treated differently" by other
(non-standard) functions.

Why would one do this? So that the reader can associate each symbol with
its position in an input file, in order to produce better error messages
when, for example, an unbound variable is used. It's not the only way to
do this, of course, but I can see some advantages.

I am dubious of the idea that non-standard extensions can have a direct
influence on the interpretation of the standard.

Regards,

Alan
Received on Fri Nov 24 2006 - 16:56:12 UTC