-- Hoogle documentation, generated by Haddock
-- See Hoogle, http://www.haskell.org/hoogle/


-- | Generalization of filter and catMaybes
--   
@package witherable
@version 0.1.2


-- | This module generalizes filterable containers.
module Data.Witherable

-- | Like <tt>traverse</tt>, but you can remove elements instead of
--   updating them.
--   
--   <pre>
--   traverse f ≡ wither (fmap Just . f)
--   </pre>
--   
--   A definition of <a>wither</a> must satisfy the following laws:
--   
--   <ul>
--   <li><i><i>identity</i></i> <tt>wither (pure . Just) ≡ pure</tt></li>
--   <li><i><i>composition</i></i> <tt>Compose . fmap (wither f) . wither g
--   ≡ wither (Compose . fmap (maybe (pure Nothing) f) . g)</tt></li>
--   </ul>
--   
--   Parametricity implies the naturality law:
--   
--   <pre>
--   t . wither f = wither (t . f)
--   </pre>
--   
--   Minimal complete definition: <a>wither</a> or <a>catMaybes</a>. The
--   default definitions can be overriden for efficiency.
class Traversable t => Witherable t where wither f = fmap catMaybes . traverse f catMaybes = runIdentity . wither pure filterA f = wither (\ a -> (\ b -> if b then Just a else Nothing) <$> f a) filter f = runIdentity . filterA (Identity . f)
wither :: (Witherable t, Applicative f) => (a -> f (Maybe b)) -> t a -> f (t b)
catMaybes :: Witherable t => t (Maybe a) -> t a
filterA :: (Witherable t, Applicative f) => (a -> f Bool) -> t a -> f (t a)
filter :: Witherable t => (a -> Bool) -> t a -> t a
witherM :: (Witherable t, Monad m) => (a -> MaybeT m b) -> t a -> m (t b)

-- | <a>blightM</a> is <a>witherM</a> with its arguments flipped.
blightM :: (Monad m, Witherable t) => t a -> (a -> MaybeT m b) -> m (t b)
instance Witherable Seq
instance Witherable Vector
instance Witherable (Const r)
instance Witherable Proxy
instance (Eq k, Hashable k) => Witherable (HashMap k)
instance Ord k => Witherable (Map k)
instance Witherable IntMap
instance Witherable []
instance Monoid e => Witherable (Either e)
instance Witherable Maybe