%{
#define YYERROR_VERBOSE
void yyerror(char *);
%}
%verbose
%token COMMAND ID KEYWORD ILLEGAL_CHAR
%%
rule:             COMMAND optional_keyword '(' ID ')'
                ;
optional_keyword: /* empty */
                | '(' KEYWORD ')'
                ;
%%
void yyerror(char *msg) {
    printf("\n%s\n", msg);
}
int main() {
    return yyparse();
}