On Sun, Jan 9, 2011 at 10:11 PM, Lennart Augustsson
<lenn...@augustsson.net>wrote:
> That looks like it looses the efficiency of the underlying representation.
>
Yes, I don't think one can retain that cleanly without using restricted
monads to exclude things like
liftM ($42) (mplus (return pred) (return succ))
or just
liftM ($42) (return pred)
Maybe one can hack something to achieve
mplus :: Ord a => Set a -> Set a -> Set a
mplus a b = Set (\k -> S.union (a >>- ret) (b >>- ret) `bind` k)
where
ret = S.singleton
bind = flip Data.Foldable.foldMap
mplus :: not (Ord a) => Set a -> Set a -> Set a
mplus a b = Set (\k -> S.union (a >>- k) (b >>- k))
using overloading with undecidable instances (?) (and defining a Monoid
instance for the Set monad in terms of the MonadPlus instance)
Reminds me of instance chains.. [1]
Sebastian
[1]: http://portal.acm.org/citation.cfm?id=1863596
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