[r6rs-discuss] set-car!

From: William D Clinger <will>
Date: Sat, 23 Jun 2007 14:26:19 -0400

Anton van Straaten wrote:
> In what sense, then, is this "a standard way to redefine standard
> procedures"?

It is a standard way to redefine the standard
procedures as perceived by the user program.

If you reexamine Alan Watson's reply to Carl
Eastland on Friday, 22 June, and my reply to
Watson's message, you will see that both of us
were talking about ways to guarantee that a user
program does not use set-car! or set-cdr!. In
R5RS Scheme, that is easy: just redefine them at
the very beginning of the program. With the R6RS,
there does not appear to be any standard or even
portable way to do it.

> If the quoted claim is interpreted as merely an indirect way of saying
> that R5RS allows any top-level variable to be mutated, then it's clearly
> true and uncontroversial.

The R5RS does not allow any top-level variable to be
assigned. It only allows top-level variables to be
defined, and of course they can be assigned after
that. I'm glad we were able to agree this is true
and noncontroversial.

Will
Received on Sat Jun 23 2007 - 14:26:19 UTC