/// <summary>
        /// LR(1)的Closure操作。
        /// 补全一个状态。
        /// </summary>
        /// <param name="grammar"></param>
        /// <param name="state"></param>
        /// <returns></returns>
        static SmallerLR1State Closure(this RegulationList grammar, SmallerLR1State state,
                                       Dictionary <TreeNodeType, bool> nullableDict = null, FIRSTCollection firstCollection = null)
        {
            if (nullableDict == null)
            {
                grammar.GetNullableDict(out nullableDict);
            }
            if (firstCollection == null)
            {
                grammar.GetFirstCollection(out firstCollection, nullableDict);
            }

            Queue <LR1Item> queue = new Queue <LR1Item>();

            foreach (var item in state)
            {
                queue.Enqueue(item);
            }
            while (queue.Count > 0)
            {
                LR1Item      item = queue.Dequeue();
                TreeNodeType node = item.GetNodeNext2Dot();
                if (node == null || node.IsLeave)
                {
                    continue;
                }

                List <TreeNodeType> betaZ     = item.GetBetaZ();
                FIRST             first       = grammar.GetFirst(firstCollection, nullableDict, betaZ);
                List <Regulation> regulations = grammar.GetRegulations(node);
                foreach (var regulation in regulations)
                {
                    foreach (var value in first.Values)
                    {
                        LR1Item newItem = new LR1Item(regulation, 0, value);
                        if (state.TryInsert(newItem))
                        {
                            queue.Enqueue(newItem);
                        }
                    }
                }
            }

            return(state);
        }