public Value get(Identifier id) {
	// traverse the list of environments backwards
	for(int i = env.size() - 1; i >= 0; i--) {
	    Value rval = env.get(i).get(id);
	    if(rval != null) {
		return rval;
	    }
	}
	// exited the search without finding the Identifier, return null
	return null;
    }