[r6rs-discuss] "Unspecified"

[Anton van Straaten]

John Cowan wrote:
> Anton van Straaten scripsit:
> 
> 
>>A value named "unspecified" (or #<unspecified>, #!unspecified etc.) is 
>>used by Chicken, Larceny, and SCM, at least.  Others (in addition to 
>>Scheme 48) use some variant such as "unspecific".  Others, of course, 
>>use a variation on "void", apparently borrowed from C.
> 
> 
> The current implementation of Chicken does not have any such read-syntax.
> If forced to (as by display), the unspecified value will print as
> #<unspecified>, but it can't be reread.  

I didn't intend to imply that such read syntax existed.  Note that the 
R6RS draft say in section 9.8 that the unspecified value "is not a datum 
value, and thus has no external representation".  ("Datum values" are 
defined in 1.9.)

> However, the core procedure
> "void" returns the unspecified value when invoked.

This corresponds to the R6RS procedure "unspecified".

BTW, I'm curious, when you wrote "the unspecified value" in that 
sentence, whether you did so explicitly in the R6RS sense, or whether 
that just seemed the natural thing to write.

Anton