[Haskell-cafe] Generalized null / zero

1. Is there a more general version of `null`? (e.g. for a Monad, Functor, Applicative, Traversable or the like.) The closest I can come up with is, in decreasing clunkiness: zero :: (MonadPlus m, Eq (m a)) => m a -> Bool zero = m == mzero zero :: (Alternative f, Eq (f a)) => f a -> Bool zero = m == empty zero :: (Monoid m, Eq m) => m -> Bool zero = m == mempty Though requiring Eq seems ugly and unnecessary, in theory. 2. In that vein, is there an existing function for "a value or a default if it's zero"? E.g.: orElse :: (Monoid m) => m -> m -> m a `orElse` b = if zero a then b else a Thank you, Alvaro http://alva.ro