用Yacc实现语法分析器-4-编译原理

用Yacc实现语法分析器

一、实验目的

掌握语法分析器的构造原理，掌握Yacc的编程方法。

二、实验内容

用Yacc编写一个语法分析程序，使之与词法分析器结合，能够根据语言的上下文无关文法，识别输入的单词序列是否文法的句子。

program → block

block → { stmts }

stmts →　stmt stmts | e

stmt → id= expr ;

| if ( bool ) stmt

| if ( bool) stmt else stmt

| while (bool) stmt

| do stmt while (bool ) ;

| break ;

| block

bool → expr < expr

| expr <= expr

| expr > expr

| expr >= expr

| expr

expr → expr + term

| expr - term

| term

term → term * factor

| term / factor

| factor

factor → ( expr ) | id| num　

三、实验步骤及结果

实验环境：unix

实验结果：按归约的先后顺序显示每次归约时所使用的产生式。

部分代码：

用于产生flex输入的代码

View Code

Test.l:[a-zA-Z_][a-zA-Z_0-9]* {return ID;}

[0-9]+\.[0-9]+ {return REAL;}

[0-9]+ {return NUM;}

"||" {return OR;}

"&&" {return AND;}

"|" {return '|';}

"&" {return '&';}

"<=" {return LE;}

"<" { return '<';}

">=" {return GE;}

">" {return '>';}

"!=" {return NE;}

"=" { return '=';}

"==" {return EQ;}

"\+"  {return '+';}

"\-" {return '-';}

"\*" {return '*';}

"\/" {return '/';}

"(" {return '(';}

")" {return ')';}

";" {return ';';}

"{" {return '{';}

"}" {return '}';}

"[" {return '['; }

"]" {return ']';}

Test.y:rel : expr '<' expr { printf("rel-->expr<expr\n"); }

    | expr LE expr { printf("rel-->expr<=expr\n"); }

       | expr GE expr { printf("rel-->expr>=expr\n"); }

       | expr '>' expr { printf("rel-->expr>expr\n"); }

       | expr { printf("rel-->expr\n"); }

       ;

expr : expr '+' term { printf("expr-->expr+term\n"); }

     | expr '-' term { printf("expr-->expr-term\n"); } 

        | term { printf("expr-->term\n"); }

        ;

term : term '*' unary { printf("term-->term*unary\n"); }

     | term '/' unary { printf("term-->term/unary\n"); }

        | unary { printf("term-->unary\n"); }

        ;

unary : '!' unary { printf("unary-->!unary\n"); }

      | '-' unary %prec UMINUS{ printf("unary-->-unary\n"); }

         | factor { printf("unary-->factor\n"); }

         ;

factor : '(' bool ')' { printf("factor-->(bool)\n"); }

       | loc { printf("factor-->loc\n"); }

          | NUM { printf("factor-->num\n"); }

          | REAL { printf("factor-->real\n"); }

          | TRUE { printf("factor-->true\n"); }

          | FALSE { printf("factor-->false\n"); }

Flex生成代码:

View Code

Test.l:[a-zA-Z_][a-zA-Z_0-9]* {return ID;}

[0-9]+\.[0-9]+ {return REAL;}

[0-9]+ {return NUM;}

"||" {return OR;}

"&&" {return AND;}

"|" {return '|';}

"&" {return '&';}

"<=" {return LE;}

"<" { return '<';}

">=" {return GE;}

">" {return '>';}

"!=" {return NE;}

"=" { return '=';}

"==" {return EQ;}

"\+"  {return '+';}

"\-" {return '-';}

"\*" {return '*';}

"\/" {return '/';}

"(" {return '(';}

")" {return ')';}

";" {return ';';}

"{" {return '{';}

"}" {return '}';}

"[" {return '['; }

"]" {return ']';}

Test.y:rel : expr '<' expr { printf("rel-->expr<expr\n"); }

    | expr LE expr { printf("rel-->expr<=expr\n"); }

       | expr GE expr { printf("rel-->expr>=expr\n"); }

       | expr '>' expr { printf("rel-->expr>expr\n"); }

       | expr { printf("rel-->expr\n"); }

       ;

expr : expr '+' term { printf("expr-->expr+term\n"); }

     | expr '-' term { printf("expr-->expr-term\n"); } 

        | term { printf("expr-->term\n"); }

        ;

term : term '*' unary { printf("term-->term*unary\n"); }

     | term '/' unary { printf("term-->term/unary\n"); }

        | unary { printf("term-->unary\n"); }

        ;

unary : '!' unary { printf("unary-->!unary\n"); }

      | '-' unary %prec UMINUS{ printf("unary-->-unary\n"); }

         | factor { printf("unary-->factor\n"); }

         ;

factor : '(' bool ')' { printf("factor-->(bool)\n"); }

       | loc { printf("factor-->loc\n"); }

          | NUM { printf("factor-->num\n"); }

          | REAL { printf("factor-->real\n"); }

          | TRUE { printf("factor-->true\n"); }

          | FALSE { printf("factor-->false\n"); }

Yacc生成部分代码：

View Code

#line 1334 "y.tab.c"

  yyvsp -= yylen;

  yyssp -= yylen;

  YY_STACK_PRINT (yyss, yyssp);

  *++yyvsp = yyval;

  /* Now `shift' the result of the reduction.  Determine what state

     that goes to, based on the state we popped back to and the rule

     number reduced by.  */

 

  yyn = yyr1[yyn];

 

  yystate = yypgoto[yyn - YYNTOKENS] + *yyssp;

  if (0 <= yystate && yystate <= YYLAST && yycheck[yystate] == *yyssp)

    yystate = yytable[yystate];

  else

    yystate = yydefgoto[yyn - YYNTOKENS];

 

  goto yynewstate;

 

 

/*------------------------------------.

| yyerrlab -- here on detecting error |

`------------------------------------*/

yyerrlab:

  /* If not already recovering from an error, report this error.  */

  if (!yyerrstatus)

    {

      ++yynerrs;

#if YYERROR_VERBOSE

      yyn = yypact[yystate];

 

      if (YYPACT_NINF < yyn && yyn < YYLAST)

       {

         YYSIZE_T yysize = 0;

         int yytype = YYTRANSLATE (yychar);

         const char* yyprefix;

         char *yymsg;

         int yyx;

 

         /* Start YYX at -YYN if negative to avoid negative indexes in

            YYCHECK.  */

         int yyxbegin = yyn < 0 ? -yyn : 0;

 

         /* Stay within bounds of both yycheck and yytname.  */

         int yychecklim = YYLAST - yyn;

         int yyxend = yychecklim < YYNTOKENS ? yychecklim : YYNTOKENS;

         int yycount = 0;

 

         yyprefix = ", expecting ";

         for (yyx = yyxbegin; yyx < yyxend; ++yyx)

           if (yycheck[yyx + yyn] == yyx && yyx != YYTERROR)

             {

              yysize += yystrlen (yyprefix) + yystrlen (yytname [yyx]);

              yycount += 1;

              if (yycount == 5)

                {

                  yysize = 0;

                  break;

                }

             }

         yysize += (sizeof ("syntax error, unexpected ")

                   + yystrlen (yytname[yytype]));

         yymsg = (char *) YYSTACK_ALLOC (yysize);

         if (yymsg != 0)

           {

             char *yyp = yystpcpy (yymsg, "syntax error, unexpected ");

             yyp = yystpcpy (yyp, yytname[yytype]);

 

             if (yycount < 5)

              {

                yyprefix = ", expecting ";

                for (yyx = yyxbegin; yyx < yyxend; ++yyx)

                  if (yycheck[yyx + yyn] == yyx && yyx != YYTERROR)

                    {

                     yyp = yystpcpy (yyp, yyprefix);

                     yyp = yystpcpy (yyp, yytname[yyx]);

                     yyprefix = " or ";

                    }

              }

             yyerror (yymsg);

             YYSTACK_FREE (yymsg);

           }

         else

           yyerror ("syntax error; also virtual memory exhausted");

       }

      else

例如，程序片断

{

i = 2;

while (i <=100)

{

sum = sum + i;

i = i + 2;

}

（注：原本是在windwos环境下编程，最后到unix环境下，发现速度快了，灵活性高了，同时方便了很多。（flex，bison））

test.l

View Code

%option noyywrap
%{
#include<stdlib.h>
#include<ctype.h>
#include<stdio.h>
%}
%%
"if" {return IF;} 
"while" {return WHILE;} 
"do" {return DO;} 
"break" {return BREAK;}
"int"|"float"|"bool"|"char" {return BASIC;}
"true" {return TRUE;}
"false" {return FALSE;}
"else"  {return ELSE;}
[a-zA-Z_][a-zA-Z_0-9]* {return ID;}
[0-9]+\.[0-9]+ {return REAL;}
[0-9]+ {return NUM;}
"||" {return OR;}
"&&" {return AND;}
"|" {return '|';}
"&" {return '&';}
"<=" {return LE;}
"<" { return '<';}
">=" {return GE;}
">" {return '>';}
"!=" {return NE;}
"=" { return '=';}
"==" {return EQ;}
"\+"  {return '+';}
"\-" {return '-';}
"\*" {return '*';}
"\/" {return '/';}
"(" {return '(';}
")" {return ')';}
";" {return ';';}
"{" {return '{';}
"}" {return '}';}
"[" {return '['; }
"]" {return ']';}
"//".*  {}
[ \n\t] {}
%%

test.y

View Code

%{
#include<ctype.h>
#include<stdio.h>
%}
%left '+' '-'
%left '*' '/'
%nonassoc UMINUS
%token NUM AND BASIC BREAK DO ELSE EQ FALSE GE
%token ID IF INDEX LE MINUS NE OR REAL TRUE WHILE
KET
 %token  RIGHT_BRA
%%
program : block { printf("program-->block\n"); }
        ;
block : '{' decls stmts '}' { printf("block-->{decls stmts}\n"); }
      ;
decls : decls decl { printf("decls-->decls decl\n"); }
      | /*empty*/
      ;
decl : type ID ';' { printf("decl-->type id;\n"); }
     ;
type : type '[' NUM ']' { printf("type-->type[num]\n"); }
     | BASIC { printf("type-->basic\n"); }
     ;
stmts : stmts stmt { printf("stmts-->stmts stmt\n"); }
     | /*empty*/
     ;
stmt : DO stmt WHILE '(' bool ')' ';' { printf("stmt-->do stmt while(bool);\n"); }
     | IF '(' bool ')' stmt { printf("stmt--if(bool)stmt\n"); }
     | IF '(' bool ')' stmt ELSE stmt { printf("stmt-->if(bool)stmt else stmt\n"); }
     | WHILE '(' bool ')' stmt { printf("stmt-->while(bool)stmt\n"); }
     | BREAK ';' { printf("stmt-->break;\n"); }
     | block { printf("stmt-->block\n"); }
     | loc '=' bool ';' { printf("stmt-->loc=bool;\n"); }
     ;
loc : loc '[' bool ']' { printf("loc-->loc[bool]\n"); }
    | ID { printf("loc-->id\n"); }
    ;
bool : bool OR join { printf("bool-->bool||join\n"); }
     | join { printf("bool-->join\n"); }
     ;
join : join AND equality { printf("join-->join&&equality\n"); }
     | equality { printf("join-->equality\n"); }
     ;
equality : equality EQ rel { printf("equality-->equality==rel\n"); }
         | equality NE rel { printf("equality-->equality!=rel\n"); }
         | rel { printf("equality-->rel\n"); }
         ;
rel : expr '<' expr { printf("rel-->expr<expr\n"); }
    | expr LE expr { printf("rel-->expr<=expr\n"); } 
    | expr GE expr { printf("rel-->expr>=expr\n"); }
    | expr '>' expr { printf("rel-->expr>expr\n"); }
    | expr { printf("rel-->expr\n"); }
    ;
expr : expr '+' term { printf("expr-->expr+term\n"); }
     | expr '-' term { printf("expr-->expr-term\n"); }  
     | term { printf("expr-->term\n"); }
     ;
term : term '*' unary { printf("term-->term*unary\n"); }
     | term '/' unary { printf("term-->term/unary\n"); }
     | unary { printf("term-->unary\n"); }
     ;
unary : '!' unary { printf("unary-->!unary\n"); }
      | '-' unary %prec UMINUS{ printf("unary-->-unary\n"); }
      | factor { printf("unary-->factor\n"); }
      ;
factor : '(' bool ')' { printf("factor-->(bool)\n"); }
       | loc { printf("factor-->loc\n"); }
       | NUM { printf("factor-->num\n"); }
       | REAL { printf("factor-->real\n"); }
       | TRUE { printf("factor-->true\n"); }
       | FALSE { printf("factor-->false\n"); }
       ;
       
%%
#include "lex.yy.c"
int  main()
{
 extern FILE *yyin;
 yyin=fopen("b.txt","r");
 yyparse();
 return 0;
}
yyerror(char *s)
{
    printf("%s error!\n",s);
}

b.txt

View Code

{
    i = 2;
    while (i <=100)
    {
        sum = sum + i;
        i = i + 2;
    }
}

在unix可以生成a.out就能直接用。

《Lex与Yacc》中文第二版(带源码)_yacc_flex_两份文档：http://pan.baidu.com/share/link?shareid=167248&uk=1678594189

实验4 secomd time 晋级版（）：http://pan.baidu.com/share/link?shareid=167252&uk=1678594189

posted @ 2012-12-16 17:36 xjx_user 阅读(4336) 评论(1) 编辑收藏举报

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用Yacc实现语法分析器-4-编译原理

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