递归下降的基本思想：

为每一个非终结符构造一个子程序，每一个子程序的过程体中按该产生式的候选项分情况展开，遇到终结符直接匹配，而遇到非终结符就调用相应非终结符的子程序。该分析从调用文法开始符号的子程序开始，直到所有非终结符都展开为终结符并得到匹配为止。若分析过程中达到这一步则表明分析成功，否则表明输入中有语法错误。递归下降分析对文法的限制是不能有公共左因子和左递归。由于文法是递归定义的，因此子程序也是递归的，被称为递归下降子程序。

-The basic idea of recursive descent:

　　For each non-terminal construct a subroutine, each subroutine of the process of the body produced by the sub-type of candidate to undertake encountered terminator direct match, while the case of non-terminal symbol on the call to the corresponding non-terminal symbol of the subroutine. The analysis from the grammar start symbol of the subroutine call to start until all the non-terminal and launched as a terminator and get matched up. If the analysis process to achieve this step indicates that the analysis of success, or else that there is a syntax error input. Recursive descent analysis of the grammar of the restrictions can not have public left factor and left recursion. As the grammar is a recursive definition, and therefore also a recursive subroutine, known as recursive descent subprogram.