[Chicken-users] continuing callback confusion

[Elliot Cuzzillo]

I've been trying for a while now to get a main C program to get
compiled with a Scheme program and call a Scheme callback. My current
attempt follows; I just modified one of the embedding examples, so I
wouldn't get the embedding part wrong.

x2.scm:
-------------
(require-extension srfi-18 easyffi)

(define-external (foo (c-string x)) int (string-length x))
(define (x) (+ 1 2));

(define m (make-mutex))

(define (t)
 (mutex-lock! m)
 (thread-sleep! 1)
 (print (thread-name (current-thread)))
 (mutex-unlock! m)
 (t) )

(thread-start! (make-thread t 'PING!))
(thread-start! (make-thread t 'PONG!))

(let loop ()
 (return-to-host)
 (thread-yield!)
 (loop) )


y2.c:
--------------
#include "chicken.h"
extern int foo(char* blah);
int main()
{
 C_word k = CHICKEN_run(C_toplevel);
 char x[6];
 x[0] = 'h';
 x[1] = 'o';
 x[2] = 'w';
 x[3] = 'd';
 x[4] = 'y';
 x[5] = 0;

 for(;;) {
   k = CHICKEN_continue(k);
   foo(x);
 }

 return 0;
}

-----------------
To compile:
csc x2.scm y2.c -embedded

-------------------
It segfaults whenever I have a call to foo(x) anywhere; I've tried
doing it outside the for loop, before the call to CHICKEN_continue, as
well as where it is now. It segfaults before printing PING!, which
seems odd.
I also tried it without the extern keyword.

I would very much like to know what I'm doing wrong, so that I can
finally call a Scheme function from C. I also think it would be good
to add an example of this to the wiki, because, unless I am being very
stupid, it is not completely obvious how to do this.

Thanks,
Elliot