PARSER_BEGIN(parens1)

public class parens1 {

    public static int pairs_of_parens = 0;

    public static void main(String args[]) throws ParseException {
        int result;
        parens1 parser = new parens1(System.in);
        parser.parentheses();
        System.out.println("Pairs of parentheses = " + parser.pairs_of_parens);
    }
}
PARSER_END(parens1)

SKIP : 
{
        " "
|       "\n"
}

TOKEN : 
{
        < LPAREN: "("   >
|       < RPAREN: ")"   >
}

void parentheses():
{}
{
   <LPAREN> parentheses() <RPAREN> { pairs_of_parens++; }
|                                  {       }
}