-----------------------------------------------------------------------------
-- |
-- Module      :  Data.Traversable
-- Copyright   :  Conor McBride and 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 traversed from left to right,
-- performing an action on each element.  Instances are expected to satisfy
-- the listed [laws](#laws).
-----------------------------------------------------------------------------

module Data.Traversable (
    -- * The 'Traversable' class
    Traversable(..),
    -- * Utility functions
    for,
    forM,
{-
    forAccumM,
    mapAccumL,
    mapAccumR,
    mapAccumM,
    -- * General definitions for superclass methods
    fmapDefault,
    foldMapDefault,
-}
    ) where
import Prelude()              -- do not import Prelude
import Primitives
import Control.Applicative
import Control.Monad(Monad(..), MonadPlus(..))
--import Data.Coerce
import Data.Either
import Data.Foldable
import Data.Function
import Data.Functor
import Data.Functor.Const
import Data.Functor.Identity
--import Data.Functor.Utils ( StateL(..), StateR(..), StateT(..), (#.) )
import Data.List_Type
import qualified Data.List as List
import Data.Maybe
import Data.Monoid
import Data.Proxy
--import Data.Ord ( Down(..) )
--import Data.Proxy ( Proxy(..) )

class (Functor t, Foldable t) => Traversable (t :: Type -> Type) where

    traverse :: forall (f :: Type -> Type) a b . Applicative f => (a -> f b) -> t a -> f (t b)
    traverse f = sequenceA . fmap f

    sequenceA :: forall (f :: Type -> Type) a . Applicative f => t (f a) -> f (t a)
    sequenceA = traverse id

    mapM :: forall (m :: Type -> Type) a b . Monad m => (a -> m b) -> t a -> m (t b)
    mapM = traverse

    sequence :: forall (m :: Type -> Type) a . Monad m => t (m a) -> m (t a)
    sequence = sequenceA

instance Traversable Maybe where
  traverse _ Nothing = pure Nothing
  traverse f (Just x) = Just <$> f x

instance Traversable [] where
  traverse f = List.foldr cons_f (pure [])
    where cons_f x ys = liftA2 (:) (f x) ys

instance forall a . Traversable (Either a) where
  traverse _ (Left x) = pure (Left x)
  traverse f (Right y) = Right <$> f y

instance Traversable Identity where
  traverse f (Identity a) = Identity <$> f a

instance Traversable Proxy where
  traverse _ _ = pure Proxy

instance forall m . Traversable (Const m) where
  traverse _ (Const m) = pure $ Const m

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

-- | @since 4.7.0.0
instance Traversable ((,) a) where
    traverse f (x, y) = (,) x <$> f y

-- | @since 2.01
instance Ix i => Traversable (Array i) where
    traverse f arr = listArray (bounds arr) `fmap` traverse f (elems arr)

-- | @since 4.7.0.0
instance Traversable Proxy where
    traverse _ _ = pure Proxy
    {-# INLINE traverse #-}
    sequenceA _ = pure Proxy
    {-# INLINE sequenceA #-}
    mapM _ _ = pure Proxy
    {-# INLINE mapM #-}
    sequence _ = pure Proxy
    {-# INLINE sequence #-}

-- | @since 4.7.0.0
instance Traversable (Const m) where
    traverse _ (Const m) = pure $ Const m

-- | @since 4.8.0.0
instance Traversable Dual where
    traverse f (Dual x) = Dual <$> f x

-- | @since 4.8.0.0
instance Traversable Sum where
    traverse f (Sum x) = Sum <$> f x

-- | @since 4.8.0.0
instance Traversable Product where
    traverse f (Product x) = Product <$> f x

-- | @since 4.8.0.0
instance Traversable First where
    traverse f (First x) = First <$> traverse f x

-- | @since 4.8.0.0
instance Traversable Last where
    traverse f (Last x) = Last <$> traverse f x

-- | @since 4.12.0.0
instance (Traversable f) => Traversable (Alt f) where
    traverse f (Alt x) = Alt <$> traverse f x

-- | @since 4.12.0.0
instance (Traversable f) => Traversable (Ap f) where
    traverse f (Ap x) = Ap <$> traverse f x

-- | @since 4.9.0.0
instance Traversable ZipList where
    traverse f (ZipList x) = ZipList <$> traverse f x


-- Instances for GHC.Generics
-- | @since 4.9.0.0
instance Traversable U1 where
    traverse _ _ = pure U1
    {-# INLINE traverse #-}
    sequenceA _ = pure U1
    {-# INLINE sequenceA #-}
    mapM _ _ = pure U1
    {-# INLINE mapM #-}
    sequence _ = pure U1
    {-# INLINE sequence #-}

-- | @since 4.9.0.0
deriving instance Traversable V1

-- | @since 4.9.0.0
deriving instance Traversable Par1

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

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

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

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

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

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

-- | @since 4.9.0.0
deriving instance Traversable UAddr

-- | @since 4.9.0.0
deriving instance Traversable UChar

-- | @since 4.9.0.0
deriving instance Traversable UDouble

-- | @since 4.9.0.0
deriving instance Traversable UFloat

-- | @since 4.9.0.0
deriving instance Traversable UInt

-- | @since 4.9.0.0
deriving instance Traversable UWord

-- Instance for Data.Ord
-- | @since 4.12.0.0
deriving instance Traversable Down
-}
-- general functions

-- | 'for' is 'traverse' with its arguments flipped. For a version
-- that ignores the results see 'Data.Foldable.for_'.
for :: forall (t :: Type -> Type) (f :: Type -> Type) a b . (Traversable t, Applicative f) => t a -> (a -> f b) -> f (t b)
for = flip traverse

forM :: forall (t :: Type -> Type) (m :: Type -> Type) a b . (Traversable t, Monad m) => t a -> (a -> m b) -> m (t b)
forM = flip mapM

{-
mapAccumL :: forall t s a b. Traversable t
          => (s -> a -> (s, b)) -> s -> t a -> (s, t b)
mapAccumL f s t = coerce (traverse @t @(StateL s) @a @b) (flip f) t s

mapAccumR :: forall t s a b. Traversable t
          => (s -> a -> (s, b)) -> s -> t a -> (s, t b)
mapAccumR f s t = coerce (traverse @t @(StateR s) @a @b) (flip f) t s

mapAccumM
  :: forall m t s a b. (Monad m, Traversable t)
  => (s -> a -> m (s, b))
  -> s -> t a -> m (s, t b)
mapAccumM f s t = coerce (mapM @t @(StateT s m) @a @b) (StateT #. flip f) t s

forAccumM
  :: (Monad m, Traversable t)
  => s -> t a -> (s -> a -> m (s, b)) -> m (s, t b)
forAccumM s t f = mapAccumM f s t

-}

fmapDefault :: forall t a b . Traversable t
            => (a -> b) -> t a -> t b
fmapDefault f = runIdentity . traverse (Identity . f)

foldMapDefault :: forall t m a . (Traversable t, Monoid m)
               => (a -> m) -> t a -> m
foldMapDefault f = getConst . traverse (Const . f)