values in a non-values context

values in a non-values context

[Matt Wette]

I've looked in some RnRS documents and can't find answer to the following:
Is the value of a `values' expression in a non-values context defined?
In Guile, `(write (values 1 2 3))' generates `1'.  Does the language standard
specify this or is this determined by implementation?  In other words, is it
OK to count on this behavior?

Matt

Re: values in a non-values context

[John Cowan]

It's determined by the implementation.  <
https://bitbucket.org/cowan/r7rs-wg1-infra/src/default/MultipleValues.md>
lists what several implementations actually do.  Many similar pages are
accessible from <
https://bitbucket.org/cowan/r7rs-wg1-infra/src/default/ImplementationContrasts.md
>.

On Thu, Jun 14, 2018 at 8:56 PM, Matt Wette <matt.wette@gmail.com> wrote:

> I've looked in some RnRS documents and can't find answer to the following:
> Is the value of a `values' expression in a non-values context defined?
> In Guile, `(write (values 1 2 3))' generates `1'.  Does the language
> standard
> specify this or is this determined by implementation?  In other words, is
> it
> OK to count on this behavior?
>
> Matt
>
>
>

Re: values in a non-values context

[Ludovic Courtès]

Hi,

John Cowan <cowan@ccil.org> skribis:

> It's determined by the implementation.  <
> https://bitbucket.org/cowan/r7rs-wg1-infra/src/default/MultipleValues.md>
> lists what several implementations actually do.  Many similar pages are
> accessible from <
> https://bitbucket.org/cowan/r7rs-wg1-infra/src/default/ImplementationContrasts.md
>>.

Indeed.  The choice starting with Guile 2.0 was to automatically
truncate multiple value returns in accordance with the number of values
expected by the continuation.

You can rely on multiple-value truncation in Guile, but be aware that
other Schemes may behave differently.

Ludo’.