On the other hand, it's difficult or impossible to make a list of a bunch of different types of things that have nothing in common save being members of the class.
I've recently been playing with making, for each class C, a "interface" datatype IC (appropriately universally and existentially qualified so as to include a dictionary for class C), and then making this IC an instance of class C. Then I can wrap any instance of C up in an IC, and make a list of those. The casts get a bit annoying, though; the compiler can't figure out that this IC is in some sense the maximum type in class C, and so can't resolve things like f :: MyClass a => [a] -> b f = ... upcast :: MyClass a => a -> IMyClass -- usually defined as an instance of class Cast upcast x = IMyClass x f [upcast a, upcast b] -- yields type error Instead, you have to redefine f as follows: f' :: [IMyClass] -> b which is a bit annoying. HTH. --KW 8-)