{-# LANGUAGE CPP #-}
{-# LANGUAGE Rank2Types #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE UndecidableInstances #-}
{-# OPTIONS_GHC -Wno-redundant-constraints #-}

-----------------------------------------------------------------------------

-- |

-- Module      :  Control.Lens.Internal.Fold

-- Copyright   :  (C) 2012-2016 Edward Kmett

-- License     :  BSD-style (see the file LICENSE)

-- Maintainer  :  Edward Kmett <ekmett@gmail.com>

-- Stability   :  experimental

-- Portability :  non-portable

--

----------------------------------------------------------------------------

module Control.Lens.Internal.Fold
  (
  -- * Monoids for folding

    Folding(..)
  , Traversed(..)
  , TraversedF(..)
  , Sequenced(..)
  , Leftmost(..), getLeftmost
  , Rightmost(..), getRightmost
  , ReifiedMonoid(..)
  -- * Semigroups for folding

  , NonEmptyDList(..)
  ) where

import Prelude ()

import Control.Lens.Internal.Getter
import Control.Lens.Internal.Prelude
import Data.Functor.Bind
import Data.Maybe (fromMaybe)
import Data.Reflection

import qualified Data.List.NonEmpty as NonEmpty

------------------------------------------------------------------------------

-- Folding

------------------------------------------------------------------------------


-- | A 'Monoid' for a 'Contravariant' 'Applicative'.

newtype Folding f a = Folding { forall (f :: * -> *) a. Folding f a -> f a
getFolding :: f a }

instance (Contravariant f, Applicative f) => Semigroup (Folding f a) where
  Folding f a
fr <> :: Folding f a -> Folding f a -> Folding f a
<> Folding f a
fs = forall (f :: * -> *) a. f a -> Folding f a
Folding (f a
fr forall (f :: * -> *) a b. Applicative f => f a -> f b -> f b
*> f a
fs)
  {-# INLINE (<>) #-}

instance (Contravariant f, Applicative f) => Monoid (Folding f a) where
  mempty :: Folding f a
mempty = forall (f :: * -> *) a. f a -> Folding f a
Folding forall (f :: * -> *) a. (Contravariant f, Applicative f) => f a
noEffect
  {-# INLINE mempty #-}
#if !(MIN_VERSION_base(4,11,0))
  Folding fr `mappend` Folding fs = Folding (fr *> fs)
  {-# INLINE mappend #-}
#endif

------------------------------------------------------------------------------

-- Traversed

------------------------------------------------------------------------------


-- | Used internally by 'Control.Lens.Traversal.traverseOf_' and the like.

--

-- The argument 'a' of the result should not be used!

newtype Traversed a f = Traversed { forall a (f :: * -> *). Traversed a f -> f a
getTraversed :: f a }

-- See 4.16 Changelog entry for the explanation of "why not Apply f =>"?

instance Applicative f => Semigroup (Traversed a f) where
  Traversed f a
ma <> :: Traversed a f -> Traversed a f -> Traversed a f
<> Traversed f a
mb = forall a (f :: * -> *). f a -> Traversed a f
Traversed (f a
ma forall (f :: * -> *) a b. Applicative f => f a -> f b -> f b
*> f a
mb)
  {-# INLINE (<>) #-}

instance Applicative f => Monoid (Traversed a f) where
  mempty :: Traversed a f
mempty = forall a (f :: * -> *). f a -> Traversed a f
Traversed (forall (f :: * -> *) a. Applicative f => a -> f a
pure (forall a. HasCallStack => [Char] -> a
error [Char]
"Traversed: value used"))
  {-# INLINE mempty #-}
#if !(MIN_VERSION_base(4,11,0))
  Traversed ma `mappend` Traversed mb = Traversed (ma *> mb)
  {-# INLINE mappend #-}
#endif

------------------------------------------------------------------------------

-- TraversedF

------------------------------------------------------------------------------


-- | Used internally by 'Control.Lens.Fold.traverse1Of_' and the like.

--

-- @since 4.16

newtype TraversedF a f = TraversedF { forall a (f :: * -> *). TraversedF a f -> f a
getTraversedF :: f a }

instance Apply f => Semigroup (TraversedF a f) where
  TraversedF f a
ma <> :: TraversedF a f -> TraversedF a f -> TraversedF a f
<> TraversedF f a
mb = forall a (f :: * -> *). f a -> TraversedF a f
TraversedF (f a
ma forall (f :: * -> *) a b. Apply f => f a -> f b -> f b
.> f a
mb)
  {-# INLINE (<>) #-}

instance (Apply f, Applicative f) => Monoid (TraversedF a f) where
  mempty :: TraversedF a f
mempty = forall a (f :: * -> *). f a -> TraversedF a f
TraversedF (forall (f :: * -> *) a. Applicative f => a -> f a
pure (forall a. HasCallStack => [Char] -> a
error [Char]
"TraversedF: value used"))
  {-# INLINE mempty #-}
#if !(MIN_VERSION_base(4,11,0))
  TraversedF ma `mappend` TraversedF mb = TraversedF (ma *> mb)
  {-# INLINE mappend #-}
#endif

------------------------------------------------------------------------------

-- Sequenced

------------------------------------------------------------------------------


-- | Used internally by 'Control.Lens.Traversal.mapM_' and the like.

--

-- The argument 'a' of the result should not be used!

--

-- See 4.16 Changelog entry for the explanation of "why not Apply f =>"?

newtype Sequenced a m = Sequenced { forall a (m :: * -> *). Sequenced a m -> m a
getSequenced :: m a }

instance Monad m => Semigroup (Sequenced a m) where
  Sequenced m a
ma <> :: Sequenced a m -> Sequenced a m -> Sequenced a m
<> Sequenced m a
mb = forall a (m :: * -> *). m a -> Sequenced a m
Sequenced (m a
ma forall (m :: * -> *) a b. Monad m => m a -> m b -> m b
>> m a
mb)
  {-# INLINE (<>) #-}

instance Monad m => Monoid (Sequenced a m) where
  mempty :: Sequenced a m
mempty = forall a (m :: * -> *). m a -> Sequenced a m
Sequenced (forall (m :: * -> *) a. Monad m => a -> m a
return (forall a. HasCallStack => [Char] -> a
error [Char]
"Sequenced: value used"))
  {-# INLINE mempty #-}
#if !(MIN_VERSION_base(4,11,0))
  Sequenced ma `mappend` Sequenced mb = Sequenced (ma >> mb)
  {-# INLINE mappend #-}
#endif

------------------------------------------------------------------------------

-- NonEmptyDList

------------------------------------------------------------------------------


newtype NonEmptyDList a
  = NonEmptyDList { forall a. NonEmptyDList a -> [a] -> NonEmpty a
getNonEmptyDList :: [a] -> NonEmpty.NonEmpty a }

instance Semigroup (NonEmptyDList a) where
  NonEmptyDList [a] -> NonEmpty a
f <> :: NonEmptyDList a -> NonEmptyDList a -> NonEmptyDList a
<> NonEmptyDList [a] -> NonEmpty a
g = forall a. ([a] -> NonEmpty a) -> NonEmptyDList a
NonEmptyDList ([a] -> NonEmpty a
f forall b c a. (b -> c) -> (a -> b) -> a -> c
. forall a. NonEmpty a -> [a]
NonEmpty.toList forall b c a. (b -> c) -> (a -> b) -> a -> c
. [a] -> NonEmpty a
g)

------------------------------------------------------------------------------

-- Leftmost and Rightmost

------------------------------------------------------------------------------


-- | Used for 'Control.Lens.Fold.firstOf'.

data Leftmost a = LPure | LLeaf a | LStep (Leftmost a)

instance Semigroup (Leftmost a) where
  Leftmost a
x <> :: Leftmost a -> Leftmost a -> Leftmost a
<> Leftmost a
y = forall a. Leftmost a -> Leftmost a
LStep forall a b. (a -> b) -> a -> b
$ case Leftmost a
x of
    Leftmost a
LPure    -> Leftmost a
y
    LLeaf a
_  -> Leftmost a
x
    LStep Leftmost a
x' -> case Leftmost a
y of
      -- The last two cases make firstOf produce a Just as soon as any element

      -- is encountered, and possibly serve as a micro-optimisation; this

      -- behaviour can be disabled by replacing them with _ -> x <> y'.

      -- Note that this means that firstOf (backwards folded) [1..] is Just _|_.

      Leftmost a
LPure    -> Leftmost a
x'
      LLeaf a
a  -> forall a. a -> Leftmost a
LLeaf forall a b. (a -> b) -> a -> b
$ forall a. a -> Maybe a -> a
fromMaybe a
a (forall a. Leftmost a -> Maybe a
getLeftmost Leftmost a
x')
      LStep Leftmost a
y' -> forall a. Monoid a => a -> a -> a
mappend Leftmost a
x' Leftmost a
y'

instance Monoid (Leftmost a) where
  mempty :: Leftmost a
mempty = forall a. Leftmost a
LPure
  {-# INLINE mempty #-}
#if !(MIN_VERSION_base(4,11,0))
  mappend = (<>)
  {-# INLINE mappend #-}
#endif

-- | Extract the 'Leftmost' element. This will fairly eagerly determine that it can return 'Just'

-- the moment it sees any element at all.

getLeftmost :: Leftmost a -> Maybe a
getLeftmost :: forall a. Leftmost a -> Maybe a
getLeftmost Leftmost a
LPure = forall a. Maybe a
Nothing
getLeftmost (LLeaf a
a) = forall a. a -> Maybe a
Just a
a
getLeftmost (LStep Leftmost a
x) = forall a. Leftmost a -> Maybe a
getLeftmost Leftmost a
x

-- | Used for 'Control.Lens.Fold.lastOf'.

data Rightmost a = RPure | RLeaf a | RStep (Rightmost a)

instance Semigroup (Rightmost a) where
  Rightmost a
x <> :: Rightmost a -> Rightmost a -> Rightmost a
<> Rightmost a
y = forall a. Rightmost a -> Rightmost a
RStep forall a b. (a -> b) -> a -> b
$ case Rightmost a
y of
    Rightmost a
RPure    -> Rightmost a
x
    RLeaf a
_  -> Rightmost a
y
    RStep Rightmost a
y' -> case Rightmost a
x of
      -- The last two cases make lastOf produce a Just as soon as any element

      -- is encountered, and possibly serve as a micro-optimisation; this

      -- behaviour can be disabled by replacing them with _ -> x <> y'.

      -- Note that this means that lastOf folded [1..] is Just _|_.

      Rightmost a
RPure    -> Rightmost a
y'
      RLeaf a
a  -> forall a. a -> Rightmost a
RLeaf forall a b. (a -> b) -> a -> b
$ forall a. a -> Maybe a -> a
fromMaybe a
a (forall a. Rightmost a -> Maybe a
getRightmost Rightmost a
y')
      RStep Rightmost a
x' -> forall a. Monoid a => a -> a -> a
mappend Rightmost a
x' Rightmost a
y'

instance Monoid (Rightmost a) where
  mempty :: Rightmost a
mempty = forall a. Rightmost a
RPure
  {-# INLINE mempty #-}
#if !(MIN_VERSION_base(4,11,0))
  mappend = (<>)
  {-# INLINE mappend #-}
#endif

-- | Extract the 'Rightmost' element. This will fairly eagerly determine that it can return 'Just'

-- the moment it sees any element at all.

getRightmost :: Rightmost a -> Maybe a
getRightmost :: forall a. Rightmost a -> Maybe a
getRightmost Rightmost a
RPure = forall a. Maybe a
Nothing
getRightmost (RLeaf a
a) = forall a. a -> Maybe a
Just a
a
getRightmost (RStep Rightmost a
x) = forall a. Rightmost a -> Maybe a
getRightmost Rightmost a
x