从 TinyC 编译器学习 Flex & Bison 的用法

%{
Prologue
%}

Bison declarations

%%
Grammar rules
%%
Epilogue

%{
#define YYSTYPE char *
#include "y.tab.h"
int cur_line = 1;
void yyerror(const char *msg);
void unrecognized_char(char c);
#define _DUPTEXT {yylval = strdup(yytext);}
%}

/* note \042 is '"' */

OPERATOR        ([-/+*()=,;])
INTEGER         ([0-9]+)
STRING          (\042[^\042\n]*\042)
IDENTIFIER      ([_a-zA-Z][_a-zA-Z0-9]*)
WHITESPACE      ([ \t]*)

%%
{OPERATOR}      { return yytext[0]; }
"int"           { return T_Int; }
"print"         { return T_Print; }

{INTEGER}       { _DUPTEXT; return T_IntConstant; }
{STRING}        { _DUPTEXT; return T_StringConstant; }
{IDENTIFIER}    { _DUPTEXT; return T_Identifier; }

{WHITESPACE}    { /* ignore every whitespace */ }
\n              { cur_line++; }
.               { unrecognized_char(yytext[0]); }
%%

int yywrap(void) { 
    return 1;
}

void unrecognized_char(char c) {
    char buf[32] = "Unrecognized character: ?";
    buf[24] = c;
    yyerror(buf);
}

void yyerror(const char *msg) {
    printf("Error at line %d:\n\t%s\n", cur_line, msg);
    exit(-1);
}

%{
#include <stdio.h>
#include <stdlib.h>
void yyerror(const char*);
#define YYSTYPE char *
%}

%token T_StringConstant T_IntConstant T_Identifier T_Int T_Print

%left '+' '-'
%left '*' '/'
%right U_neg

%%

S:   
    Stmt                        { /* empty */ }
|   S Stmt                      { /* empty */ }
;

Stmt:
    VarDecl ';'                 { printf("\n\n"); }
|   Assign                      { /* empty */ }
|   Print                       { /* empty */ }
;

VarDecl:
    T_Int T_Identifier          { printf("var %s", $2); }
|   VarDecl ',' T_Identifier    { printf(", %s", $3); }
;

Assign:
    T_Identifier '=' E ';'      { printf("pop %s\n\n", $1); }
;

Print:
    T_Print '(' T_StringConstant Actuals ')' ';'
                                { printf("print %s\n\n", $3); }
;

Actuals:
    /* empty */                 { /* empty */ }
|   Actuals ',' E               { /* empty */ }
;

E:
    E '+' E                     { printf("add\n"); }
|   E '-' E                     { printf("sub\n"); }
|   E '*' E                     { printf("mul\n"); }
|   E '/' E                     { printf("div\n"); }
|   '-' E %prec U_neg           { printf("neg\n"); }
|   T_IntConstant               { printf("push %s\n", $1); }
|   T_Identifier                { printf("push %s\n", $1); }
|   '(' E ')'                   { /* empty */ }
;

%%

int main() {
    return yyparse();
}