private String peekToken() {
	if (token == null) 
	    try {
		while (st == null || !st.hasMoreTokens()) {
		    line = r.readLine();
		    if (line == null) return null;
		    st = new StringTokenizer(line);
		}
		token = st.nextToken();
	    } catch (IOException e) { }
	return token;
    }