CS>$generator(scan)
CS>{
CS>  node* n;
CS>  scan( node* root = 0 ): n(root) {}
CS>  $emit(int)
CS>    for(;n; n = n->next)
CS>    {
CS>      $yield(n->value);
CS>      if( n->kid )
CS>        $restart( n = n->kid );
CS>    }
CS>  $stop
CS>};
CS>