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Re: Strings from C?

From: Matthias Koeppe
Subject: Re: Strings from C?
Date: Wed, 17 Oct 2001 17:19:54 +0200
User-agent: Gnus/5.090004 (Oort Gnus v0.04) Emacs/20.6

"Robert A. Uhl" <address@hidden> writes:

> On Wed, Oct 17, 2001 at 11:21:11AM +0200, Matthias Koeppe wrote:
>> You might want to consider using an interface generator like SWIG 1.3
>> ( or g-wrap.  This may save some work, and both
>> tools know how to perform standard conversions between C and Scheme
>> values.
> Well, part of my problem is that in several places my methods take
> GSList* (a singly-linked list from glib, for those who don't use that
> library) as either an argument or return value.  I was tempted to use
> SWIG, but everything I saw indicated that there was no way to convert
> between _my_ lists and guile's lists.  Given that my application is
> list-intensive, and that scheme is list-intensive, it would seem
> pointless to simply wrap up more functions to create C lists from
> scheme lists; something like:
> (trav-mapobject-set-owners obj (gslist-new obj2 obj3 obj4))
> or
> (car (gslist-split (trav-mapobject-get-owners obj)))
> is more than a little ugly, at least to my eyes.


> Perh. there is a way to do this from SWIG after all?  Obviously
> ideal would be able to write:
> (trav-mapobject-set-owners obj '(obj2 obj3 obj4))
> and
> (car (trav-mapobject-get-owners obj))

In SWIG we have user-defined type conversions between arbitrary C and
Scheme types, so-called "typemaps".  The SWIG code for your specific
conversion problem would look like this:

       %typemap(in) GSList * {
         GSList *list = $source;
         SCM scheme_list = ... /* build the SCM list here */
         $target = scheme_list;

       %typemap(out) GSList * {
         SCM scheme_list = $source;
         GSList *list = ... /* build GSList here */
         $target = list;

If you make these typemap declarations, all functions taking or
returning GSList * values will automatically perform the conversion,
so you can write your Scheme code in the "ideal" way.

Matthias Köppe --
SWIG makes Guile wrappers for C/C++ libs --
ILISP does module-aware Emacs/Guile interaction --

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