[R6RS] Unbound variables

[William D Clinger]

Mike wrote:
> 4.1.1   reference to unbound variable  error       should &undefined
> 5.2.1   set! (unbound variable)        error       should &undefined (!!!!!)
> 5.2.1   set! (w/o defining)            unspecified should &undefined (!!!!!)
> 
> At least within a library module, I vote for turning these
> "should"s into "must"s.

Kent wrote:
> I agree and would make one further change.  Within a
> library, there shouldn't be any unbound variables, just
> unbound identifiers, and an unbound identifier should be
> treated as a syntax error and cause a &syntax exception
> to be raised, since there's no way of knowing what kind
> of identifier it is and no reason for treating it as any
> particular kind.

I agree with Mike and Kent, but would like to make sure
everyone agrees that this vote includes assignments to
variables that are bound but not defined within the
library.  (An example would be an assignment to cons,
imported from the core language, or to any variable that
is imported from some other library.)  In particular, I
want to make sure everyone is voting for this exception
that must be raised to be a &syntax exception, not some
kind of run-time exception.

Will