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《实验2 递归下降语法分析.ppt》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。
1、编译技术实验(2)递归下降语法分析周尔强2015年10月exp:factor
2、exp'+'factor
3、exp'-'factor;factor:term
4、factor'*'term
5、factor'/'term;term:NUMBER
6、'-'term;递归下降分析举例Zhou,Erqiang2SchoolofInformationandSoftwareEngineeringexp:factor
7、exp'+'factor
8、exp'-'factor;递归下降分析举例Zhou,Erqiang3SchoolofInformationandSoftwareEng
9、ineering语言：factor+/-factor+/-factor...程序：voidexp(){factor();while(tok=='+'
10、
11、tok=='-'){advance();factor();}}+/-factor+/-factor...重复出现的部分factor:term
12、factor'*'term
13、factor'/'term;递归下降分析举例Zhou,Erqiang4SchoolofInformationandSoftwareEngineering语言：term*/term*/term...程序：voidfactor(){ter
14、m();while(tok=='*'
15、
16、tok=='/'){advance();term();}}*/term*/term...重复出现的部分term:NUMBER
17、'-'term;递归下降分析举例Zhou,Erqiang5SchoolofInformationandSoftwareEngineering语言：NUMBER、-NUMBER--NUMBER、---NUMBER程序：voidterm(){if(tok==NUMBER);advance();elseif(tok=='-'){advance();term();}elseerror();}纯粹
18、的语法分析只分析词法记号序列是否符合语言的文法如-5+20*5-3实际的编译器需要找出词法记号序列的结构即语法树递归下降分析举例Zhou,Erqiang6SchoolofInformationandSoftwareEngineeringexp:factor
19、exp'+'factor
20、exp'-'factor;factor:term
21、factor'*'term
22、factor'/'term;term:NUMBER
23、'-'term;递归下降文法举例Zhou,Erqiang7SchoolofInformationandSoftwareEngineering-
24、5+20*5-3termtermtermtermfactorfactorexptermfactorexpfactorexp递归下降文法举例Zhou,Erqiang8SchoolofInformationandSoftwareEngineering-5+20*5-3termtermtermtermfactorfactorexptermfactorexpfactorexpnull5205-*+3-抽象的语法树（AbstractSyntaxTree,AST）whileb≠0ifa>ba:=a−belseb:=b−areturna抽象语法树Zhou,Erqi
25、ang9SchoolofInformationandSoftwareEngineering抽象语法树结点设计所有树结点统一为一个结构类型如何区别结点：赋值语句？选择语句？结点内需要用标志位结点的最大分支数表达式最多为二元运算，至少2个结点为树的叶结点需要保存运算的数值表达式的抽象语法树Zhou,Erqiang10SchoolofInformationandSoftwareEngineering抽象语法树结点设计表达式的抽象语法树Zhou,Erqiang11SchoolofInformationandSoftwareEngineeringtypedef
26、struct_astast;typedefstruct_ast*past;struct_ast{intivalue;char*nodeType;pastleft;pastright;};递归下降分析函数表达式的抽象语法树Zhou,Erqiang12SchoolofInformationandSoftwareEngineeringvoidfactor(){term();while(tok=='*'
27、
28、tok=='/'){advance();term();}}pastastFactor(){pastl=astTerm();while(tok=='*'
29、
30、
31、tok=='/'){intoper=tok;advance();pastr=astTerm();l=newE
