[Haskell-cafe] classes for data structures

Hi, I've been working a lot with maps, sets and lists. While the process of getting things out of them is abstracted by foldable, traversable and friends, the process of building one up is not. Would it be possible to have something like: class Buildable b where empty :: b a --makes an empty b with elements of type a insert :: a -> b a -> b a --inserts the new element into the buildable I'm not particularly wedded to the names. It's just that it would be very convenient sometimes to collect data items into e.g. a list or a set, without pushing in some klunky foralled insert function. I see that this is realted to MonadPlus, but the space of possible container classes is wider than that of monads e.g. set. Matthew