[r6rs-discuss] set-car!

From: AndrevanTonder <andre>
Date: Sat, 23 Jun 2007 11:47:35 -0400 (EDT)

On Sat, 23 Jun 2007, William D Clinger wrote:

> For example, you can redefine set-car! and set-cdr!
> without changing the behavior of any system procedures
> that might happen to use them. Redefining them will
> certainly make their original values inaccessible to
> the rest of your program, unless of course their
> original values had been captured by some part of the
> program prior to the redefinition.
>
> That is a fundamental aspect of R5RS Scheme. One would
> hope the editors understand the magnitude of the changes
> they have introduced in the draft R6RS.

But does r6rs guarantee that the meaning of standard
procedures other than set-car! and set-cdr! will be changed
by replacing (rnrs mutable-pairs (6))?

If r6rs doesn't guarantee it, r6rs effectively prohibits
using such a "feature" in portable programs. Given this
effective prohibition, the situation will not be so different
from r5rs for the behaviour of portable programs, except
that stuff that used to be implementation responsibility
in r5rs becomes the user's responsibility in the draft r6rs.

ANdre
Received on Sat Jun 23 2007 - 11:47:35 UTC