Re: MonadPlus instance for ContT

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Edward Kmett writes:

The third construction is the 'universal' lifting that works for every Applicative, which would look like:

instance (Monad m, Monoid a) => Monoid (ContT r m a) where   mempty = return mempty   mappend = liftM2 mappend

Why not then this? That is, once AMP is out... instance (Applicative m, Monoid a) => Monoid (m a) where mempty = pure mempty mappend = liftA2 mappend -- John Wiegley FP Complete Haskell tools, training and consulting http://fpcomplete.com johnw on #haskell/irc.freenode.net