    {-# LANGUAGE CPP #-}
    {-# LANGUAGE Rank2Types #-}
    {-# LANGUAGE FlexibleContexts #-}
    {-# LANGUAGE MultiParamTypeClasses #-}
    #ifdef TRUSTWORTHY
    {-# LANGUAGE Trustworthy #-}
    #endif
    -------------------------------------------------------------------------------
    -- |
    -- Module      :  Data.Vector.Lens
    -- Copyright   :  (C) 2012-15 Edward Kmett
    -- License     :  BSD-style (see the file LICENSE)
    -- Maintainer  :  Edward Kmett <ekmett@gmail.com>
    -- Stability   :  provisional
    -- Portability :  non-portable
    --
    -- This module provides lenses and traversals for working with generic
    -- vectors.
    -------------------------------------------------------------------------------
    module Data.Vector.Lens
      ( toVectorOf
      -- * Isomorphisms
      , vector
      , forced
      -- * Lenses
      , sliced
      -- * Traversal of individual indices
      , ordinals
      ) where

    import Control.Applicative
    import Control.Lens
    import Control.Lens.Internal.List (ordinalNub)
    import Data.Vector as Vector hiding (zip, filter, indexed)
    import Prelude hiding ((++), length, null, head, tail, init, last, map, reverse)
    import Data.Monoid

    -- | @sliced i n@ provides a 'Lens' that edits the @n@ elements starting
    -- at index @i@ from a 'Lens'.
    --
    -- This is only a valid 'Lens' if you do not change the length of the
    -- resulting 'Vector'.
    --
    -- Attempting to return a longer or shorter vector will result in
    -- violations of the 'Lens' laws.
    --
    -- >>> Vector.fromList [1..10] ^. sliced 2 5 == Vector.fromList [3,4,5,6,7]
    -- True
    --
    -- >>> (Vector.fromList [1..10] & sliced 2 5 . mapped .~ 0) == Vector.fromList [1,2,0,0,0,0,0,8,9,10]
    -- True
    sliced :: Int -- ^ @i@ starting index
           -> Int -- ^ @n@ length
           -> Lens' (Vector a) (Vector a)
    sliced i n f v = f (slice i n v) <&> \ v0 -> v // zip [i..i+n-1] (toList v0)
    {-# INLINE sliced #-}

    -- | Similar to 'toListOf', but returning a 'Vector'.
    --
    -- >>> toVectorOf both (8,15) == Vector.fromList [8,15]
    -- True
    toVectorOf :: Getting (Endo [a]) s a -> s -> Vector a
    toVectorOf l s = fromList (toListOf l s)
    {-# INLINE toVectorOf #-}

    -- | Convert a list to a 'Vector' (or back)
    --
    -- >>> [1,2,3] ^. vector == Vector.fromList [1,2,3]
    -- True
    --
    -- >>> [1,2,3] ^. vector . from vector
    -- [1,2,3]
    --
    -- >>> Vector.fromList [0,8,15] ^. from vector . vector == Vector.fromList [0,8,15]
    -- True
    vector :: Iso [a] [b] (Vector a) (Vector b)
    vector = iso fromList toList
    {-# INLINE vector #-}

    -- | Convert a 'Vector' to a version that doesn't retain any extra
    -- memory.
    forced :: Iso (Vector a) (Vector b) (Vector a) (Vector b)
    forced = iso force force
    {-# INLINE forced #-}

    -- | This 'Traversal' will ignore any duplicates in the supplied list
    -- of indices.
    --
    -- >>> toListOf (ordinals [1,3,2,5,9,10]) $ Vector.fromList [2,4..40]
    -- [4,8,6,12,20,22]
    ordinals :: [Int] -> IndexedTraversal' Int (Vector a) a
    ordinals is f v = fmap (v //) $ traverse (\i -> (,) i <$> indexed f i (v ! i)) $ ordinalNub (length v) is
    {-# INLINE ordinals #-}