(define struct-test
   (c-lambda () struct-test "struct test x; ___result = x;")) 

But if i run the test script with this function, i get a
segmentation fault immediately.

There is also another option which comes in my mind:

(define struct-test
   (c-lambda () struct-test "struct test x; ___result_voidstar = &x;"))

This is e.g. running the allocation loop. But it will segfault when
quiting the script with CTRL + X.

But it would be great, if we could clarify later the proper usage of
structs in the ffi. I've gotten curious about that. :)