[GUI] State, Attributes and Some basic widgets

[Alastair Reid]

Axel Simon <A.Simon@ukc.ac.uk> writes:
> One question which I asked earlier is: a) Shall the classes containt
> the widget's functionality as well? (Or, alternatively: b) Shall we
> have a class for each attribute (like "onActivate") and create
> instances for all widgets that implement it.)

Having the type system detect use of unsupported attributes is highly
desirable but having a separate class for each attribute is
unappealing since I expect there's a lot of them.  Just one of the
disadvantages is that type signatures get very, very long so you're
disinclined to write them and error messages get quite outrageously
long (I once got a two-page long error message from Hugs when using
T-Rex).

Is there some way to cluster the member functions so that each class
provides multiple attributes and to use inheritance to further reduce
the size of contexts one typically writes?  In particular, can we
exploit the inheritance hierarchy in the widget sets we are building
on?

--
Alastair