Re: GIT version: values writing

[Hans Aberg]

On 20 Jan 2011, at 16:16, Ludovic Courtès wrote:

> > There seems to be a bug in GIT version when writing the 'values' data
> > type.
> >  (list 2 (values 3 4) 5)
> >  $1 = (2 3 5)
>
> This behavior is correct: in Guile 1.9, multiple-value returns are
> truncated any time the continuation expects fewer values.
>
> Here, the ‘values’ call returns 3 values, but the location where it’s
> called expects only 1, hence the automatic truncation.

After the post, I saw that R5RS says the behavior is undefined.

However, quietly loosing values is inviting bugs.

> > with the value 4 lost In guile-1.8.8, it would write
> >  (2 #<values 3 4> 5)
>
> The special “values” type in older Guile versions was an artifact of
> Guile’s implementation of multiple value support; objects of that type
> are normally invisible to user code, but they would show up in such
> situations (R5RS doesn’t specify what to do in these cases, so it was
> valid, but implementation-specific behavior.)

The old style is a reification of the values, and could be turned into  
a tuples object. The latter is what I am implementing, but I can make  
my own type instead.

It is discussed here, along with some other ideas.

https://groups.google.com/group/comp.lang.scheme/browse_thread/thread/b72d987aa6626cd2/e2f7cfa55fb51d55?hl=en