-----------------------------------------------------------------------------
-- |
-- Module      :  Data.Foldable
-- Copyright   :  Ross Paterson 2005
-- License     :  BSD-style (see the LICENSE file in the distribution)
--
-- Maintainer  :  libraries@haskell.org
-- Stability   :  stable
-- Portability :  portable
--
-- Class of data structures that can be folded to a summary value.
--
-----------------------------------------------------------------------------

module Data.Foldable (
    Foldable(..),
    -- * Special biased folds
    foldrM,
    foldlM,
    -- * Folding actions
    -- ** Applicative actions
    traverse_,
    for_,
    sequenceA_,
    asum,
    -- ** Monadic actions
    mapM_,
    forM_,
    sequence_,
    msum,
    -- * Specialized folds
    concat,
    concatMap,
    and,
    or,
    any,
    all,
    maximumBy,
    minimumBy,
    -- * Searches
    notElem,
    find
    ) where
import Prelude()              -- do not import Prelude
import Primitives
import Control.Applicative(Applicative(..), Alternative(..))
import Control.Error
import Control.Monad(Monad(..), MonadPlus(..))
import Data.Bool
import Data.Either
import Data.Eq
import Data.Foldable.Internal
import Data.Function
import Data.Functor.Const
import Data.Functor.Identity
import Data.List_Type hiding (concatMap)
import qualified Data.List as List
import Data.Maybe
import Data.Monoid
import Data.Monoid.Internal hiding (Max(..), Min(..))
import Data.Num
import Data.Ord
import Data.Proxy

infix  4 `elem`, `notElem`

class Foldable (t :: Type -> Type) where
    {-# MINIMAL foldMap | foldr #-}

    fold :: forall m . Monoid m => t m -> m
    fold = foldMap id

    foldMap :: forall m a . Monoid m => (a -> m) -> t a -> m
    foldMap f = foldr (mappend . f) mempty

    foldMap' :: forall m a . Monoid m => (a -> m) -> t a -> m
    foldMap' f = foldl' (\ acc a -> acc <> f a) mempty

    foldr :: forall a b . (a -> b -> b) -> b -> t a -> b
    foldr f z t = appEndo (foldMap (Endo . f) t) z

    foldr' :: forall a b . (a -> b -> b) -> b -> t a -> b
    foldr' f z0 = \ xs ->
        foldl (\ k x -> {-oneShot-} (\ z -> z `seq` k (f x z)))
              id xs z0

    foldl :: forall a b . (b -> a -> b) -> b -> t a -> b
    foldl f z t = appEndo (getDual (foldMap (Dual . Endo . flip f) t)) z

    foldl' :: forall a b . (b -> a -> b) -> b -> t a -> b
    foldl' f z0 = \ xs ->
        foldr (\ x k -> {-oneShot-} (\ z -> z `seq` k (f z x)))
              id xs z0

    foldr1 :: forall a . (a -> a -> a) -> t a -> a
    foldr1 f xs = fromMaybe (error "foldr1: empty structure")
                    (foldr mf Nothing xs)
      where
        mf x m = Just (case m of
                         Nothing -> x
                         Just y  -> f x y
                      )

    foldl1 :: forall a . (a -> a -> a) -> t a -> a
    foldl1 f xs = fromMaybe (error "foldl1: empty structure")
                    (foldl mf Nothing xs)
      where
        mf m y = Just (case m of
                         Nothing -> y
                         Just x  -> f x y
                      )

    toList :: forall a . t a -> [a]
    toList t = foldr (:) [] t

    null :: forall a . t a -> Bool
    null = foldr (\_ _ -> False) True

    length :: forall a . t a -> Int
    length = foldl' (\c _ -> c+1) 0

    elem :: forall a . Eq a => a -> t a -> Bool
    elem = any . (==)

    maximum :: forall a . Ord a => t a -> a
    maximum = fromMaybe (error "maximum: empty structure") .
       getMax . foldMap' (Max . Just)

    minimum :: forall a . Ord a => t a -> a
    minimum = fromMaybe (error "minimum: empty structure") .
       getMin . foldMap' (Min . Just)

    sum :: forall a . Num a => t a -> a
    sum = getSum . foldMap' Sum

    product :: forall a . Num a => t a -> a
    product = getProduct . foldMap' Product

instance Foldable Maybe where
    foldMap = maybe mempty

    foldr _ z Nothing = z
    foldr f z (Just x) = f x z

    foldl _ z Nothing = z
    foldl f z (Just x) = f z x

instance Foldable [] where
    elem    = List.elem
    foldl   = List.foldl
    foldl'  = List.foldl'
    foldl1  = List.foldl1
    foldr   = List.foldr
    --foldr'  = List.foldr'
    foldr1  = List.foldr1
    foldMap = (mconcat .) . List.map
    fold    = mconcat
    length  = List.length
    maximum = List.maximum
    minimum = List.minimum
    null    = List.null
    product = List.product
    sum     = List.sum
    toList  = id
  
instance forall a . Foldable (Either a) where
    foldMap _ (Left _) = mempty
    foldMap f (Right y) = f y

    foldr _ z (Left _) = z
    foldr f z (Right y) = f y z

    length (Left _)  = 0
    length (Right _) = 1

    null             = isLeft

instance Foldable Proxy where
  foldMap _ _ = mempty

instance Foldable Identity where
  foldMap f (Identity a) = f a

instance forall m . Foldable (Const m) where
  foldMap _ _ = mempty

{-
-- | @since 4.15
deriving instance Foldable Solo

-- | @since 4.7.0.0
instance Foldable ((,) a) where
    foldMap f (_, y) = f y

    foldr f z (_, y) = f y z
    length _  = 1
    null _ = False

-- | @since 4.8.0.0
instance Foldable (Array i) where
    foldr = foldrElems
    foldl = foldlElems
    foldl' = foldlElems'
    foldr' = foldrElems'
    foldl1 = foldl1Elems
    foldr1 = foldr1Elems
    toList = elems
    length = numElements
    null a = numElements a == 0

-- | @since 4.7.0.0
instance Foldable Proxy where
    foldMap _ _ = mempty
    {-# INLINE foldMap #-}
    fold _ = mempty
    {-# INLINE fold #-}
    foldr _ z _ = z
    {-# INLINE foldr #-}
    foldl _ z _ = z
    {-# INLINE foldl #-}
    foldl1 _ _ = error "foldl1: Proxy"
    foldr1 _ _ = error "foldr1: Proxy"
    length _   = 0
    null _     = True
    elem _ _   = False
    sum _      = 0
    product _  = 1

-- | @since 4.8.0.0
instance Foldable Dual where
    foldMap            = coerce

    elem               = (. getDual) . (==)
    foldl              = coerce
    foldl'             = coerce
    foldl1 _           = getDual
    foldr f z (Dual x) = f x z
    foldr'             = foldr
    foldr1 _           = getDual
    length _           = 1
    maximum            = getDual
    minimum            = getDual
    null _             = False
    product            = getDual
    sum                = getDual
    toList (Dual x)    = [x]

-- | @since 4.8.0.0
instance Foldable Sum where
    foldMap            = coerce

    elem               = (. getSum) . (==)
    foldl              = coerce
    foldl'             = coerce
    foldl1 _           = getSum
    foldr f z (Sum x)  = f x z
    foldr'             = foldr
    foldr1 _           = getSum
    length _           = 1
    maximum            = getSum
    minimum            = getSum
    null _             = False
    product            = getSum
    sum                = getSum
    toList (Sum x)     = [x]

-- | @since 4.8.0.0
instance Foldable Product where
    foldMap               = coerce

    elem                  = (. getProduct) . (==)
    foldl                 = coerce
    foldl'                = coerce
    foldl1 _              = getProduct
    foldr f z (Product x) = f x z
    foldr'                = foldr
    foldr1 _              = getProduct
    length _              = 1
    maximum               = getProduct
    minimum               = getProduct
    null _                = False
    product               = getProduct
    sum                   = getProduct
    toList (Product x)    = [x]

-- | @since 4.8.0.0
instance Foldable First where
    foldMap f = foldMap f . getFirst

-- | @since 4.8.0.0
instance Foldable Last where
    foldMap f = foldMap f . getLast

-- | @since 4.12.0.0
instance (Foldable f) => Foldable (Alt f) where
    foldMap f = foldMap f . getAlt

-- | @since 4.12.0.0
instance (Foldable f) => Foldable (Ap f) where
    foldMap f = foldMap f . getAp

instance Foldable (Arg a) where
  foldMap f (Arg _ a) = f a

-- Instances for GHC.Generics
-- | @since 4.9.0.0
instance Foldable U1 where
    foldMap _ _ = mempty
    {-# INLINE foldMap #-}
    fold _ = mempty
    {-# INLINE fold #-}
    foldr _ z _ = z
    {-# INLINE foldr #-}
    foldl _ z _ = z
    {-# INLINE foldl #-}
    foldl1 _ _ = error "foldl1: U1"
    foldr1 _ _ = error "foldr1: U1"
    length _   = 0
    null _     = True
    elem _ _   = False
    sum _      = 0
    product _  = 1

-- | @since 4.9.0.0
deriving instance Foldable V1

-- | @since 4.9.0.0
deriving instance Foldable Par1

-- | @since 4.9.0.0
deriving instance Foldable f => Foldable (Rec1 f)

-- | @since 4.9.0.0
deriving instance Foldable (K1 i c)

-- | @since 4.9.0.0
deriving instance Foldable f => Foldable (M1 i c f)

-- | @since 4.9.0.0
deriving instance (Foldable f, Foldable g) => Foldable (f :+: g)

-- | @since 4.9.0.0
deriving instance (Foldable f, Foldable g) => Foldable (f :*: g)

-- | @since 4.9.0.0
deriving instance (Foldable f, Foldable g) => Foldable (f :.: g)

-- | @since 4.9.0.0
deriving instance Foldable UAddr

-- | @since 4.9.0.0
deriving instance Foldable UChar

-- | @since 4.9.0.0
deriving instance Foldable UDouble

-- | @since 4.9.0.0
deriving instance Foldable UFloat

-- | @since 4.9.0.0
deriving instance Foldable UInt

-- | @since 4.9.0.0
deriving instance Foldable UWord

-- Instances for Data.Ord
-- | @since 4.12.0.0
deriving instance Foldable Down
-}

foldrM :: forall (t :: Type -> Type) (m :: Type -> Type) a b . (Foldable t, Monad m) => (a -> b -> m b) -> b -> t a -> m b
foldrM f z0 xs = foldl c return xs z0
  where c k x z = f x z >>= k

foldlM :: forall (t :: Type -> Type) (m :: Type -> Type) a b . (Foldable t, Monad m) => (b -> a -> m b) -> b -> t a -> m b
foldlM f z0 xs = foldr c return xs z0
  where c x k z = f z x >>= k

traverse_ :: forall (t :: Type -> Type) (f :: Type -> Type) a b . (Foldable t, Applicative f) => (a -> f b) -> t a -> f ()
traverse_ f = foldr c (pure ())
  where c x k = f x *> k
        {-# INLINE c #-}

for_ :: forall (t :: Type -> Type) (f :: Type -> Type) a b . (Foldable t, Applicative f) => t a -> (a -> f b) -> f ()
for_ = flip traverse_

mapM_ :: forall (t :: Type -> Type) (m :: Type -> Type) a b . (Foldable t, Monad m) => (a -> m b) -> t a -> m ()
mapM_ f = foldr c (return ())
  where c x k = f x >> k
        {-# INLINE c #-}

forM_ :: forall (t :: Type -> Type) (m :: Type -> Type) a b . (Foldable t, Monad m) => t a -> (a -> m b) -> m ()
forM_ = flip mapM_

sequenceA_ :: forall (t :: Type -> Type) (f :: Type -> Type) a . (Foldable t, Applicative f) => t (f a) -> f ()
sequenceA_ = foldr c (pure ())
  where c m k = m *> k
        {-# INLINE c #-}

sequence_ :: forall (t :: Type -> Type) (m :: Type -> Type) a . (Foldable t, Monad m) => t (m a) -> m ()
sequence_ = foldr c (return ())
  where c m k = m >> k
        {-# INLINE c #-}

asum :: forall (t :: Type -> Type) (f :: Type -> Type) a . (Foldable t, Alternative f) => t (f a) -> f a
asum = foldr (<|>) empty

msum :: forall (t :: Type -> Type) (m :: Type -> Type) a . (Foldable t, Alternative m, MonadPlus m) => t (m a) -> m a
msum = asum

concat :: forall (t :: Type -> Type) a . Foldable t => t [a] -> [a]
concat xs = foldr (\x y -> foldr (:) y x) [] xs

concatMap :: forall (t :: Type -> Type) a b . Foldable t => (a -> [b]) -> t a -> [b]
concatMap f xs = foldr (\x b -> foldr (:) b (f x)) [] xs

and :: forall (t :: Type -> Type) . Foldable t => t Bool -> Bool
and = getAll . foldMap All

or :: forall (t :: Type -> Type) . Foldable t => t Bool -> Bool
or = getAny . foldMap Any

any :: forall (t :: Type -> Type) a . Foldable t => (a -> Bool) -> t a -> Bool
any p = getAny . foldMap (Any . p)

all :: forall (t :: Type -> Type) a . Foldable t => (a -> Bool) -> t a -> Bool
all p = getAll . foldMap (All . p)

maximumBy :: forall (t :: Type -> Type) a . Foldable t => (a -> a -> Ordering) -> t a -> a
maximumBy cmp = fromMaybe (error "maximumBy: empty structure")
  . foldl' max' Nothing
  where
    max' mx y = Just $! case mx of
      Nothing -> y
      Just x -> case cmp x y of
        GT -> x
        _ -> y

minimumBy :: forall (t :: Type -> Type)  a . Foldable t => (a -> a -> Ordering) -> t a -> a
minimumBy cmp = fromMaybe (error "minimumBy: empty structure")
  . foldl' min' Nothing
  where
    min' mx y = Just $! case mx of
      Nothing -> y
      Just x -> case cmp x y of
        GT -> y
        _ -> x

notElem :: forall (t :: Type -> Type)  a . (Foldable t, Eq a) => a -> t a -> Bool
notElem x = not . elem x

find :: forall (t :: Type -> Type) a . Foldable t => (a -> Bool) -> t a -> Maybe a
find p = getFirst . foldMap (\ x -> First (if p x then Just x else Nothing))