编译原理实验二 tiny文法的LL(1)分析

来源：互联网发布：弹跳法术升级数据编辑：程序博客网时间：2024/04/29 19:48

通过LL(1)分析方法对tiny的文法进行处理，然后输入tiny程序，进行语法分析，其中也包含了词法扫描，词法扫描使用DFA状态图的循环扫描方法。

1、文法的规范化：消除文法中的左递归和提取文法的左公因子，并且对tiny的文法进行拆解，比如一条文法有几个选择，则拆成几条，最后的文法规则整理结果如下：

0 program --> stmt-sequence1 stmt-sequence --> statement stmt'2 stmt' --> ;statement stmt'3 stmt' --> $4 statement --> if-stmt5 statement --> repeat-stmt6 statement --> assign-stmt7 statement --> read-stmt8 statement --> write-stmt9 statement --> While-stmt10 statement --> Dowhile-stmt11 statement --> for-stmt12 if-stmt --> if exp then stmt-sequence else-part' end13 else-part' --> else stmt-sequence14 else-part' --> $15 repeat-stmt --> repeat stmt-sequence until exp16 assign-stmt --> identifier := exp17 read-stmt --> read identifier18 write-stmt --> write exp19 exp --> simple-exp cmp-exp'20 cmp-exp' --> comparison-op simple-exp21 cmp-exp' --> $22 comparison-op --> <23 comparison-op --> =24 simple-exp --> term term'25 term' --> addop term26 term' --> $27 addop --> +28 addop --> -29 term --> factor factor'30 factor' --> mulop factor31 factor' --> $32 mulop --> *33 mulop --> /34 mulop --> %35 factor --> (exp)36 factor --> number37 factor --> identifier38 While-stmt --> while exp do stmt-sequence endwhile39 Dowhile-stmt --> do stmt-sequence while exp 40 for-stmt --> for identifier := simple-exp for-choose'41 for-choose' --> to simple-exp do stmt-sequence enddo42 for-choose' --> downto simple-exp do stmt-sequence enddo

注：每条文法前面的标号是自行添加上去以便查看和分析，不属于程序处理范围。其中第0条文法中program为开始符号，’$’表示空推导，” -->”表示推导符号。

2、求出终结符号集和非终结符号集

扫描文法，求出终结符号集TerminalSet，非终结符号集NonTerminalSet。其中推导符号左边的token，全都属于非终结符号集，第一遍扫描可以求出非终结符号集。然后对文法推导符号右边的token进行扫描，消除掉属于非终结符号的token，剩下的token就都属于终结符号集。处理结果如下：

终结符号集：;if then end else repeat until identifier := read write < = + - * / % ( )number while do endwhile for to enddo downto

非终结符号集：programstmt-sequence stmt' statement if-stmt else-part' repeat-stmt assign-stmtread-stmt write-stmt exp cmp-exp' comparison-op simple-exp term' addop termfactor' mulop factor While-stmt Dowhile-stmt for-stmt for-choose'

3、求出first集合

first集合的求解算法伪代码自行google，具体实现见下面附件的代码。结果如下（其中字符’$’表示空推导）：

program: if repeat identifier read write while do for stmt-sequence: if repeat identifier read write while do for stmt': ; $ statement: if repeat identifier read write while do for if-stmt: if else-part': else $ repeat-stmt: repeat assign-stmt: identifier read-stmt: read write-stmt: write exp: ( number identifier cmp-exp': $ < = comparison-op: < = simple-exp: ( number identifier term': $ + - addop: + - term: ( number identifier factor': $ * / % mulop: * / % factor: ( number identifier While-stmt: while Dowhile-stmt: do for-stmt: for for-choose': to downto

4、求出follow集合

follow集合求解算法伪代码也自行google，结果如下（其中字符’#’表示输入的结束）：

program: # stmt-sequence: # else end until endwhile while enddo stmt': # else end until endwhile while enddo statement: ; # else end until endwhile while enddo if-stmt: ; # else end until endwhile while enddo else-part': end repeat-stmt: ; # else end until endwhile while enddo assign-stmt: ; # else end until endwhile while enddo read-stmt: ; # else end until endwhile while enddo write-stmt: ; # else end until endwhile while enddo exp: then ; # ) do else end until endwhile while enddo cmp-exp': then ; # ) do else end until endwhile while enddo comparison-op: ( number identifier simple-exp: < = then ; # to downto do ) else end until endwhile while enddo term': < = then ; # to downto do ) else end until endwhile while enddo addop: ( number identifier term: + - < = then ; # to downto do ) else end until endwhile while enddo factor': + - < = then ; # to downto do ) else end until endwhile while enddo mulop: ( number identifier factor: * / % + - < = then ; # to downto do ) else end until endwhile while enddo While-stmt: ; # else end until endwhile while enddo Dowhile-stmt: ; # else end until endwhile while enddo for-stmt: ; # else end until endwhile while enddo for-choose': ; # else end until endwhile while enddo

5、构造LL(1)分析表M[A,a]算法

文法规则的序号，见步骤1中的排序