parse.y:4566
static NODE*
list_concat(head, tail)
    NODE *head, *tail;
{
    NODE *last;

    if (head->nd_next) {
	last = head->nd_next->nd_end;
    }
    else {
	last = head;
    }

    head->nd_alen += tail->nd_alen;
    last->nd_next = tail;
    if (tail->nd_next) {
	head->nd_next->nd_end = tail->nd_next->nd_end;
    }
    else {
	head->nd_next->nd_end = tail;
    }

    return head;
}
