// oh yeah, and the C-part

void cbSpaceEachPointerCallback(void *pointer, /*body,shape,contraint*/
                                C_word *data /*callback closure*/)
{
 C_word *ptr = C_alloc (C_SIZEOF_POINTER);
  C_word sp = C_mpointer (&ptr, pointer);
  C_word old = *data;
  C_save (sp);
  *data = C_callback(*data, 1);
  //printf ("old = %X\tnew = %X\n", old, *data);
}
void forEachShape (cpSpace *space, C_word callback) {
 cpSpaceEachShape (space, cbSpaceEachPointerCallback, &callback);
}