On Tue, Aug 30, 2011 at 3:26 AM, John Cowan <cowan@mercury.ccil.org> wrote:
>
> "It is an error" does not mean "an error is signalled".  It's perfectly
> fine for existing or future Schemes to store or output an undefined
> value; it just isn't portable to do so.  So it is not invasive and breaks
> nothing except user code like
>
>        (define x (set! y 32))
>
> which has no portable meaning in any case (it will not work in Racket, e.g.).

Not true, as Eli pointed out.

I'm unable to find a single implementation
which does _not_ return a single unspecified
value in these cases, despite the change in
R6RS.

--
Alex