@define list_length(x) {
  @local n;
  n = 0;
  while (1) {
   switch (x) {
   case []: return n;
   @match [_,t ...]:  printf ("here, t = %a\n",t); n = n+1; x = t; break;
   default: printf("default case x = %a\n",x); break;
   }
  }
}
x = [1,2,3];
printf("length of %a is %d\n",x,list_length(x));