[r6rs-discuss] set-car!

From: Alan Watson <alan>
Date: Fri, 22 Jun 2007 15:56:04 -0500

William D Clinger wrote:

[Interesting but non-standard means to redefine the mutable-pairs
library so that one can enforce a guarantee that pairs are not mutable.]

> A similar effect could be obtained under the R5RS by
> redefining set-car! and set-cdr!, which all conforming
> implementations must allow, but that's more awkward in
> the R5RS because there is no standard way to signal an
> error.

Let me see if I have this straight.

With the R5RS we could redefine standard procedures but we did not have
a standard way to signal an error.

With the R6RS we now have a standard way to signal an error but we no
longer have a standard way to redefine standard procedures.

Was irony really one of the guiding principles of the R6RS or is this
just one of those happy coincidences of history?

Alan
Received on Fri Jun 22 2007 - 16:56:04 UTC