Re: C error-returning functions and Guile exceptions

[Andreas Rottmann]

Greg Troxel <address@hidden> writes:

>     1.  Write a C function that wraps `read_stuff ()', checks the
>       error code returned and calls `scm_throw ()' if necessary;
>
> It would be cool to extend g-wrap to be able to do this automatically.
>
Indeed.

> There is already support (I think) for multiple return values, 
>
Yes.

> so one would need to add a return type 'errno' that is ignored if 0,
> and causes a throw if not.
>
Well, there is even something quite similiar to what Ludovic wants in
guile-gnome; GLib functions can have a GError** as last argument, and
should that get set, the wrapper raises an exception. However, I still
have to think about how that can be translated for the return value
(which is treated somewhat special).

>     2.  Find a way to make the BUFFER/READ pair translate into a return
>       value of the Scheme function.
>
This touches an area of G-Wrap that is not yet implemented: mapping
multiple arguments on the C side to a single Scheme object. I did not
yet have a real incentive to implement that, but since now there is a
real-world case where this is *really* needed (there are also
functions like that in GTK+ - up to now they have custom wrappers or
are ignored), I might give implementing it a go. So, in the G-Wrap
TODO, I've noted "multiple argument mapping" as a release goal for the
next release. Don't hold your breath, though; this feature needs some
thinking and design. I'll come up with an API proposal here soonish.

>
> One could have vector objects, but recvfrom! already has similar
> behavior, so I'd be tempted to act like that.  Strings are really
> arrays, since they have lengths and aren't NULL terminated.
>
IMO, the best match for an "octet buffer" would be an srfi-4
u8vector. 

Regards, Rotty
-- 
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