PARSER_BEGIN(Q2)

class Q2 {

  /** The size of the stack **/
  static int stackSize = 0;

  /** Standard code to call the parser
   */
  public static void main(String args[]) {

    Q2 parser;

    System.out.println("Reading from standard input . . .");
    parser = new Q2(System.in);
    try {
      parser.s();
      System.out.println("Stack size is: "+stackSize);
     } catch (ParseException e) {
      System.out.println("Encountered errors during parse.");
    }
  }   /* End of function "main" */


}

PARSER_END(Q2)



/******************/
/***** TOKENS *****/
/******************/

SKIP : /* WHITE SPACE */
{
  " " 
| "\t"
| "\n"
| "\r"
}

TOKEN :
{
  < PUSH : "push" >
| < POP : "pop">
| < SEMIC : ";" >
| < ASSIGN : ":=" >
| < NUM : (["0"-"9"])+ >
| < ID : ["a"-"z"] >
}

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

void s () : {}
{
  a() ( <SEMIC> a() )* <EOF>
}

void a() : {}
{
  <PUSH> <NUM>  { stackSize++; }
| <ID> <ASSIGN> <POP>  { if (stackSize>0) stackSize--; }
}