code: public String eatId() {
  		if (!matchId())
  			throw new BadSyntaxException();
  		String s = tok.sval;
  		nextToken();
  		return s;
  	}
docs: Throws an exception if the current token is not an identifier. Otherwise,
  returns the identifier string and moves to the next token.
  
  @return the string value of the current token