递归下降分析器的基本构造方法是，对文法的每个非终结符号，都根据其产生式的各个候选式的结构，为其编写一个对应的子程序（或函数），该子程序完成相应的非终结符对应的语法成分的识别和分析任务。因此，递归下降分析器的语法分析子程序的功能是，对某个非终结符，用规则的右部符号串去匹配输入串。分析过程是按文法规则自上而下一级一级的调用有关子程序来完成。本系统采用的就是递归下降分析方法。-The recursive descent parser constructor to each nonterminal grammar, are based on the production structure of each candidate, its preparation of a corresponding subroutine (or function), the subroutine is completed appropriate the nonterminal symbol corresponding syntax component identification and analysis tasks. Therefore, the recursive descent parser parsing subroutine is a nonterminal string of symbols, the right part of the rules to match the input string. The analysis process is a top-down level grammar rules call the subroutine. The system uses a recursive descent analysis methods.