code: private static String determineSystemRoot() throws IOException {
  		String whileyhome = System.getenv("WHILEYHOME");
  		if (whileyhome == null) {
  			System.err.println("error: WHILEYHOME environment variable not set");
  			System.exit(-1);
  		}
  		return whileyhome;
  	}
docs: Determine the system root. That is, the installation directory for the
  compiler itself.
  
  @param tool
  @return
  @throws IOException