Re: (+ (values 1 2)) should be 1

[Hans Aberg]

On 25 May 2011, at 02:25, Mark H Weaver wrote:

>> Right, but as the result is unspecified according to the standard, the
>> Guile manual suggests that the value SCM_UNSPECIFIED as an
>> interpretation of that. I merely say that I think it would be a good
>> idea.
...
> Having said all this, one could still make the case that we should
> attempt to return SCM_UNSPECIFIED from expressions whose values are
> unspecified by the standards whenever _practical_.  However, doing this
> would prevent us from implementing extensions to many aspects of the
> standard.

Then sec. 10.2.5.2 of the manual needs to be clarified. It should say if a 
returned value is SCM_UNSPECIFIED then the standard says it is unspecified, but 
not the other way around.

> Let's always keep in mind these two common rationales for unspecified
> behavior in language specifications:
> 
> * to allow more efficient implementation
> * to allow extensions to the standard

Then it agrees with this for unspecified values.

Hans