Re: Accessing multiple values from C

[Ludovic Courtès]

Hi,

Julian Graham <address@hidden> skribis:

> I was playing around with some C code that uses the new R6RS
> bytevector ports, and I noticed that there doesn't seem to be an easy
> way (a la `let-values' or `receive') to access multiple return values
> from C.  I've resorted to doing:
>
>   scm_struct_ref (foo, SCM_INUM0);
>
> ...which is almost certainly not future-proof.  All I want to do is
> access these values as a pair or list.

Values were already structs in 1.8, so that’s OK.

Perhaps this should be documented though, and C accessors could be
provided.

> Is there a Right Way to do that?

Yes: write Scheme code!  :-)

In 1.8 multiple-values were always a struct, which had to be allocated
each time multiple values were returned.  In 2.0 it’s a struct only if
it has to cross the Scheme/C boundary–otherwise the values are stored on
the VM stack.

Thanks,
Ludo’.