一种自顶向下的语法分析方法的思想，根据文法的产生式规则绘制相应的转换图，并能对之进行简化，继而构造出相应的递归下降分析器。-A kind of top-down method of syntax analysis of the idea, according to the grammar production rules mapping the corresponding conversion map and the simplification can then construct the corresponding recursive descent parser.