PARSER_BEGIN(Q3)

public class Q3 {

  /*** Main routine - just call parser ***/
  public static void main(String args[]) throws ParseException {
    Q3 parser = new Q3(System.in);
    try {
      String res = parser.s();
      if (res != null)
        System.out.println("Answer is: " + res);
    } catch (ParseException x) {
      System.out.println("Exiting due to parse error.");
      throw x;
    }
  }

}

PARSER_END(Q3)


SKIP : /*** Ignoring spaces/tabs/newlines ***/
{
    " "
  | "\t"
  | "\n"
  | "\r"
  | "\f"
}


TOKEN : 
{
  < CONCAT : "+" >
| < TAIL : "-" >
| < LBR : "(" >
| < RBR : ")" >
| < STRING : (<LETTER>)+ >
| < #LETTER : ["a"-"z","A"-"Z"] >
}


/*************************/
/***** GRAMMAR RULES *****/
/*************************/


String s() :
{
  String s;
}
{
  s=e() <EOF>
  { return s; }
}

String e() :
{
  String s1, s2;
}
{
  s1=t() ( <CONCAT> s2=t() { s1 = s1+s2;} )*
  { return s1; }
}

String t() :
{
  String s;
  Token t ;
}
{
  <TAIL> s=t()
  { 
    return s.substring(1,s.length());
  }
| t=<STRING> 
  { return t.image; }
| <LBR> s=e() <RBR>
  { return s; }
}