Question

我尝试使用flex和bison创建一个简单的解析器。它编译好并生成输出文件，但问题是它没有产生预期的结果：例如输入＆＃34;整数X：= 13＆＃34;产生语法错误和＆＃34; 13＆＃34;在下一行不应该的时候。这是我的标记器。

%{
#include <stdio.h>
#include <stdlib.h>
#include "y.tab.h"
int yyerror(char *errormsg);
%}
    number      [0-9]
digit       {number}+
letter      [a-zA-Z]
bigletter   [A-Z]
any         [a-zA-Z0-9]
identifier  {bigletter}({any))*
comm        "--"

%%
"IO.read" {return READ;}
"IO.write" {return WRITE;}
"if" {return IF;}
"loop" {return LOOP;}
"until" {return UNTIL;}
"from" {return FROM;}
"finish if" {return FINISHIF;}
"finish from" {return FINISHFROM;}
"then" {return THEN;}
"start if" {return STARTIF;}
"but if" {return BUTIF;}
"start from" {return STARTFROM;}
digit {return DIGIT;}
"=" {return EQUAL;}
":=" {return ASSIGNMENT;}
"/=" {return NE;}
"<" {return LT;}
"<=" {return LE;}
">" {return GT;}
">=" {return GE;}
"+" {return PLUS;}
"-" {return MINUS;}
"*" {return MULT;}
"/" {return DIVIDE;}
"--" {return COMM;}
";" {return SEMICOLON;}
\"(([^\"]|\\\")*[^\\])?\" {return STRING;}
{comm}({any})*{comm} {return COMMENT;}
identifier {return IDENTIFIER;}
%%

int main(void)
{
yyparse();
return 0;
}

int yywrap(void)
{
return 0;
}

int yyerror(char *errormsg)
{
fprintf(stderr, "%s\n", errormsg);
exit(1);
}

这是我的解析器：

    %{
#include <stdio.h>
#include <stdlib.h>
int yylex(void);
int yyerror(const char *s);
%}

%token TOK_EMPTY_LINE READ WRITE IF LOOP UNTIL FROM FINISHIF ENDIF FINISHFROM THEN
%token STARTIF BUTIF STARTFROM BIGLETTER DIGIT NUMBER
%token EQUAL ASSIGNMENT NE LT LE GT GE PLUS MINUS MULT DIVIDE COMM STRING
%token COMMENT LETTER IDENTIFIER SEMICOLON
%left PLUS MINUS
%left MULT DIVIDE

%%
stmts   : stmt
        | stmt SEMICOLON stmts
        ;

stmt    : if_stmt
        | from_stmt
        | assign_stmt
        | print_stmt
        | decl_stmt
        ;

if_stmt : STARTIF IF cond THEN stmts FINISHIF
        | STARTIF IF cond THEN stmts BUTIF cond THEN stmts FINISHIF
        ;

from_stmt : STARTFROM FROM decl_stmt UNTIL boolean_stmt LOOP stmt FINISHFROM
          ;

boolean_stmt : expr EQUAL expr
             | expr NE expr
             | expr GT expr
             | expr LE expr
             | expr GE expr
             ;


print_stmt  : WRITE expr 
            ;


cond    : expr relop cond
            | expr
        ;

relop   : NE
        | LE
        | LT
        | GT
        | GE
        | EQUAL
        ;

decl_stmt : DIGIT IDENTIFIER
          | DIGIT assign_stmt
          ;

assign_stmt : IDENTIFIER IDENTIFIER ASSIGNMENT expr
            ;

expr    : expr PLUS term 
        | expr MINUS term
        | term
        ;

term    : term MULT factor
        | term DIVIDE factor
        | factor
        ;

factor  : DIGIT
        | IDENTIFIER
        ;
%%
int main(void)
{
yyparse();
return 0;
}

int yywrap(void)
{
return 0;
}

int yyerror(char *errormsg)
{
fprintf(stderr, "%s\n", errormsg);
exit(1);
}

非常感谢你花时间检查我的代码！

奇怪的野牛输出

0 个答案: