[plt-scheme] Please help test version 359.100

From: Matthias Felleisen (matthias at ccs.neu.edu)
Date: Tue Nov 14 11:23:58 EST 2006

On Nov 14, 2006, at 11:16 AM, Robby Findler wrote:

> At Tue, 14 Nov 2006 11:12:51 -0500, Dave Herman wrote:
>>>>    Since the value returned by "for-each" is left unspecified
>>> But it isn't left unspecified. It is specified to be the specified
>>> thing that the r5 report just calls "unspecified". (how confusing is
>>> that?!)
>> I had thought it was only in R6RS where they explicitly specified a
>> thing called the "unspecified value," whereas in R5RS it's left  
>> ambiguous.
>> I did a quick grep of R5RS and found that the phrase "an unspecified
>> value" occurs 7 times in R5RS (all in section 6), whereas there  
>> are no
>> occurrences of "the unspecified value." The use of the indefinite
>> article "an" suggests that for *each* occurrence of the phrase, the
>> value in question may be any value.
> I'm not sure how that refutes what I wrote (was it meant to?)
> I think the relevant parts of r5rs were quoted earlier in this thread
> by Jacob and me. No grepping required.

I think it refutes it unless I misunderstood what you and Jacob are
arguing. According to your emails, a Scheme semantics uses a single
value dubbed "the-unspecified-thing" and injects it into the execution
wherever the semantics says "unspecified." For all we know, you could
use 42 at all these places.

Dave and I argue that an implementation can make up a new random value
-- as long as it is a Scheme value -- and use it wherever the semantics 
says unspecified.

If you tried to say the same thing, your English comprehension is
very different from mine.

-- Matthias

Posted on the users mailing list.