haskell -- monad with values restricted to a typeclass

Question

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Restricting a monad to a type class

I want to write a Set monad that's similar to the List monad. However, this can't be done because Set requires its types to be ordered. Is there a way to create a monad that only takes values in a particular typeclass (say, Ord)? The code I want to write is

instance Monad Set.Set where
    return a = Set.singleton a
    -- set α, function (α -> set β)
    xs >>= f = Set.fold
        (\x s -> Set.union s (f x))
        Set.empty
        xs

Thanks in advance!