public HSSFBookImpl(String bookname, InputStream is) throws IOException {
super(is);
_bookname = bookname;
FunctionResolver resolver = (FunctionResolver) BookHelper.getLibraryInstance(FunctionResolver.CLASS);
if (resolver == null) resolver = new DefaultFunctionResolver();
_evaluator = HSSFFormulaEvaluator.create(this, NoCacheClassifier.instance, resolver.getUDFFinder());
_bookEvaluator = _evaluator.getWorkbookEvaluator();
_bookEvaluator.setDependencyTracker(resolver.getDependencyTracker(this));
_functionMapper = new JoinFunctionMapper(resolver.getFunctionMapper());
_variableResolver = new JoinVariableResolver();
_helper = new HSSFWorkbookHelper(this);
}