> From: Joel Gustafson <[email protected]>
> Date: Thu, 11 May 2017 08:27:52 +0000
>
> [...]
> Specifically, there's a struct OutStream that has a member
> write_callback that I need to set.
If you are not also trying to set userdata, you are forgetting the
most important part, the ID that Scheme uses to find the Scheme
callback procedure.
> struct OutStream {
> ...
> void *userdata;
> void (*write_callback)(struct OutStream *, int min, int max);
> ...
> }
>
> In the libsoundio examples it's done directly with
> outstream->write_callback = write_callback;
> How can I declare and set a Scheme callback in a struct like this?
void
register_write_callback (struct OutStream *out, void *userdata)
{
out->userdata = userdata;
out->write_callback = write_callback_helper;
}
static void*
write_callback_helper (struct OutStream *out, int min, int max)
{
Scm_write_callback (out, min, max, out->userdata);
}
(callback (* void) write_callback
(out (* (struct OutStream)))
(min int)
(max int)
(ID (* void)))
(extern void register_write_callback
(out (* (struct OutStream)))
(ID (* void)))
(define (init-outstream out)
...
(C-call "register_write_callback" out (C-callback write-callback))
...)
(define (write-callback out min max)
...)
De-registering write-callback is left as an exercise...
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