%token VAR LPAR RPAR ADD MUL

%%

exp     :       term exp_rest
        ;

exp_rest:       /**/
        |       ADD term exp_rest
        ;

term    :       factor term_rest
        ;

term_rest:      /**/
        |       MUL factor term_rest
        ;

factor  :       VAR
        |       LPAR exp RPAR
        ;