I have tried to create read-only attributes in htoolkit. It's easy, as any of you will already know: ------------------------------------------ class GetterAttr attr where getterAttr :: attr a b -> a -> IO b instance GetterAttr Attr where getterAttr (Attr getter setter) = getter data RAttr w a = RAttr (w -> IO a) instance GetterAttr RAttr where getterAttr (RAttr getter) = getter -- | Get an attribute get :: (GetterAttr attr) => w -> attr w a -> IO a get w a = getterAttr a w -- | Define a read-only attribute. Takes the name of the attribute as its first argument. readAttr :: (w -> IO a) -> RAttr w a readAttr getter = RAttr getter --- The rest is in Attr.hs------------------------------------- I have managed to compile htk with this modification, however it turns out that there are classes in htk like -- | Widgets that has specified integer position. class Positioned w where -- | The widget position pos :: Attr w Int Now, a programmer finding an instance of this class will think that he can move the object by setting the attribute. But menus are the only instance of this class, wich I changed to pos::Rattr w Int, because menus can't be moved. This raises the problem: what if I have also "instance Positioned Window"? Well, this problem has many solutions, the simplest of wich is *not* to have statically read-only attributes. I would rather try other solutions, however they might complicate the class and type hierarchy. What do you all think about this? Vincenzo