Created
October 8, 2018 17:08
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newtype MonoidComp r m a = MonoidComp { unMonoidComp :: ContT r m a } | |
deriving (Functor, Applicative, Monad, MonadTrans) | |
instance (Applicative m, Monoid r) => Alternative (MonoidComp r m) where | |
empty = MonoidComp $ ContT $ const (pure mempty) | |
MonoidComp a <|> MonoidComp b = | |
MonoidComp $ ContT $ \f -> liftA2 (<>) (runContT a f) (runContT b f) | |
foldMapA :: (Foldable f, Applicative m, Monoid r) => (a -> m r) -> f a -> m r | |
foldMapA f = foldr (liftA2 (<>) . f) (pure mempty) | |
fromFoldable :: (Applicative m, Foldable f, Monoid r) => f a -> MonoidComp r m a | |
fromFoldable xs = MonoidComp $ ContT $ \f -> foldMapA f xs | |
runMonoidComp :: MonoidComp r m r -> m r | |
runMonoidComp = evalContT . unMonoidComp |
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