用Lex(flex)和yacc(bison)写的简单计算器

用Lex(flex)和yacc(bison)写的简单计算器(4) rexpr :REAL
         { $$ = $1; }
     rexpr PLUS rexpr
         { $$ = $1 + $3; }
     rexpr MINUS rexpr
         { $$ = $1 - $3; }
     rexpr TIMES rexpr
         { $$ = $1 * $3; }
     rexpr DIVIDE rexpr
         {
            if ($3)
                $$ = $1 / $3;
            else
            {
                $$ = $1;
                printf (stderr, "%d.%d-%d.%d: division by zero",
                           @3.first_line, @3.first_column,
                           @3.last_line, @3.last_column);
             }
           }
     rexpr POWER rexpr
       { $$ = pow($1,$3); }
     LP rexpr RP
         { $$ = $2; }
     LP rexpr error
         { $$ = $2; yyerror("missing ')'"); yyerrok;}
     MINUS rexpr %prec UNARYMINUS