public static void expr() {

         System.out.println("Enter <expr>");
            if (nextToken == 'I') term();
           else error();
            if (nextToken == '+') lex();
            if (nextToken == '(') lex();
         System.out.println("Exit <expr>");

      }

          public static void term() {

         System.out.println("Enter <term>");
            if (nextToken == 'I') factor();
            else error();
            if (nextToken == '*') lex();
            if (nextToken == 'F') lex();
            if (nextToken == ')') lex();
         System.out.println("Exit <term>");

      }

          public static void factor() {

         System.out.println("Enter <factor>");
            if (nextToken == 'I') lex();
            else error();

         System.out.println("Exit <factor>");

      }


          public static void fun() {

         System.out.println("Enter <fun>");
            lex();

         System.out.println("Exit <fun>");

      }