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calculator
%{
#include "calculator.tab.h"
using namespace std;
%}
%%
[ \t] ;
\+ { return PLUS; }
\- { return MINUS; }
\* { return MUL; }
\/ { return DIV; }
\( { return LPAREN; }
\) { return RPAREN; }
[0-9]+ { yylval.ival = atoi(yytext); return INT; }
[a-zA-Z0-9]+ {
yylval.sval = strdup(yytext);
return IDENT;
}
\n return ENDL;
. ;
%%
%{
#include <cstdio>
#include <iostream>
using namespace std;
int yylex();
extern "C" int yyparse();
extern "C" FILE *yyin;
void yyerror(char *s);
%}
%union {
int ival;
float fval;
char *sval;
}
%token ENDL PLUS MINUS MUL DIV LPAREN RPAREN
%token <ival> INT
%token <sval> IDENT
%type <ival> expression1
%type <ival> expression
%left PLUS MINUS
%left MUL DIV
%%
start:
expressions;
expressions:
expressions expression1 ENDL
| expression1 ENDL;
expression1:
expression { cout<<$1<<endl; };
expression:
expression PLUS expression { $$ = $1 + $3; }
|expression MINUS expression { $$ = $1 - $3; }
|expression MUL expression { $$ = $1 * $3; }
|expression DIV expression { $$ = $1 / $3; }
|LPAREN expression RPAREN { $$ = $2; }
| INT { $$ = $1; };
%%
int main(int argc, char *argv[]) {
if (argc!= 2) {
cout <<"Usage: <command> filename"<<endl;
return 1;
}
FILE *myfile = fopen(argv[1], "r");
if (!myfile) {
cout << "I can't open "<<argv[1]<< endl;
return -1;
}
yyin = myfile;
do {
yyparse();
} while (!feof(yyin));
}
void yyerror(char *s) {
cout << "Parse error: " << s << endl;
exit(-1);
}
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