On Fri, Sep 22, 2006 at 02:02:42AM +0000, Aubrey Jaffer wrote:
>> Date: Fri, 22 Sep 2006 10:29:31 -0400 (EDT)
>> From: AndrevanTonder <andre_at_het.brown.edu>
>>
>> Actually, I agree with another poster that it would be nice if
>> these expressions returned zero values instead of the current 1.
>> In that case, maybe a "void" "type" would not be so far-fetched for
>> such expressions (ignoring for the moment that the language is
>> untyped).
>>
>> The reason I would like it if these expressions returned zero
>> values is the following: I sometimes get hard-to-debug errors due
>> to inconsistent data values containing #<unspecified>, due to
>> obscure errors in logic, misplaced parentheses, etc. I can imagine
>> that newcomers would run into this kind of error quite a bit more
>> often.
>>
>> The problem with these errors is that they often occur long after
>> the call that inserted the #<unspecified> value in the data
>> structure. If these expressions returned no value, the error would
>> occur immediately, as it really should, and one would not be able
>> to build such inconsistent data values in the first place.
>
> That is a good idea. This was not possible in R5RS because of
>
> "Except for continuations created by the `call-with-values'
> procedure, all continuations take exactly one value."
>
> But R6RS 4.5 says:
>
> "The continuations discarding these values accept any number of
> values."
>
> The language "value returned is unspecified" would be changed to
> "returns no values"; there would be no object to name.
Is there any time where one would want to distinguish between `no
values' and `the unspecified value'?
--
Trent Buck, Student Errant
Received on Sun Oct 01 2006 - 20:09:11 UTC