sub _goto_recur {
   if ($_[0] <= 1) {
      return $_[1];
   } else {
      $_[1] *= $_[0];
      --$_[0];
      goto &_goto_recur;
   }
}

sub goto_recur {
   my ($x, $y) = (shift, 1);
   # We can't plug the constant 1 directly into $_[1]
   # since we want to change that (alias!)
   return _goto_recur($x, $y);
}