[R6RS] The unspecified values, multiple-value semantics and all that

[dyb at cs.indiana.edu]

>  *  Library procedures can't ever be sure their continuation
>     will accept zero values.  That assumption could be added
>     to their contract, but that would be an incompatible
>     change to the contracts of procedures that currently
>     return a single unspecified result.

This is the crux of the matter.  I would be inclined to make set!, write,
etc., return zero values if it weren't for the huge backward compatibility
problem it would cause.

>  *  Requiring all continuations not created by call-with-values
>     to accept zero values would solve the problem, but at least
>     two of the editors have indicated strong opposition to this.
>     If we can't even convince the editors, what chance have we
>     of convincing the community at large?

I assume you're counting me here, but my opposition isn't strong.  Having
a specified unspecified value to which zero values map in this case makes
this significantly more palatable.  I remain strongly opposed to requiring
such continuations to ignore extra values, however.

Kent