content: {-# LANGUAGE CPP, BangPatterns #-}
  {-# OPTIONS_GHC -fno-warn-incomplete-patterns #-}
  {-# OPTIONS_HADDOCK prune #-}
  #if __GLASGOW_HASKELL__ >= 701
  {-# LANGUAGE Trustworthy #-}
  #endif
  
  -- |
  -- Module      : Data.ByteString.Lazy
  -- Copyright   : (c) Don Stewart 2006
  --               (c) Duncan Coutts 2006-2011
  -- License     : BSD-style
  --
  -- Maintainer  : dons00@gmail.com, duncan@community.haskell.org
  -- Stability   : stable
  -- Portability : portable
  --
  -- A time and space-efficient implementation of lazy byte vectors
  -- using lists of packed 'Word8' arrays, suitable for high performance
  -- use, both in terms of large data quantities, or high speed
  -- requirements. Lazy ByteStrings are encoded as lazy lists of strict chunks
  -- of bytes.
  --
  -- A key feature of lazy ByteStrings is the means to manipulate large or
  -- unbounded streams of data without requiring the entire sequence to be
  -- resident in memory. To take advantage of this you have to write your
  -- functions in a lazy streaming style, e.g. classic pipeline composition. The
  -- default I\/O chunk size is 32k, which should be good in most circumstances.
  --
  -- Some operations, such as 'concat', 'append', 'reverse' and 'cons', have
  -- better complexity than their "Data.ByteString" equivalents, due to
  -- optimisations resulting from the list spine structure. For other
  -- operations lazy ByteStrings are usually within a few percent of
  -- strict ones.
  --
  -- The recomended way to assemble lazy ByteStrings from smaller parts
  -- is to use the builder monoid from "Data.ByteString.Builder".
  --
  -- This module is intended to be imported @qualified@, to avoid name
  -- clashes with "Prelude" functions.  eg.
  --
  -- > import qualified Data.ByteString.Lazy as B
  --
  -- Original GHC implementation by Bryan O\'Sullivan.
  -- Rewritten to use 'Data.Array.Unboxed.UArray' by Simon Marlow.
  -- Rewritten to support slices and use 'Foreign.ForeignPtr.ForeignPtr'
  -- by David Roundy.
  -- Rewritten again and extended by Don Stewart and Duncan Coutts.
  -- Lazy variant by Duncan Coutts and Don Stewart.
  --
  
  module Data.ByteString.Lazy (
  
          -- * The @ByteString@ type
          ByteString,             -- instances: Eq, Ord, Show, Read, Data, Typeable
  
          -- * Introducing and eliminating 'ByteString's
          empty,                  -- :: ByteString
          singleton,              -- :: Word8   -> ByteString
          pack,                   -- :: [Word8] -> ByteString
          unpack,                 -- :: ByteString -> [Word8]
          fromStrict,             -- :: Strict.ByteString -> ByteString
          toStrict,               -- :: ByteString -> Strict.ByteString
          fromChunks,             -- :: [Strict.ByteString] -> ByteString
          toChunks,               -- :: ByteString -> [Strict.ByteString]
          foldrChunks,            -- :: (S.ByteString -> a -> a) -> a -> ByteString -> a
          foldlChunks,            -- :: (a -> S.ByteString -> a) -> a -> ByteString -> a
  
          -- * Basic interface
          cons,                   -- :: Word8 -> ByteString -> ByteString
          cons',                  -- :: Word8 -> ByteString -> ByteString
          snoc,                   -- :: ByteString -> Word8 -> ByteString
          append,                 -- :: ByteString -> ByteString -> ByteString
          head,                   -- :: ByteString -> Word8
          uncons,                 -- :: ByteString -> Maybe (Word8, ByteString)
          unsnoc,                 -- :: ByteString -> Maybe (ByteString, Word8)
          last,                   -- :: ByteString -> Word8
          tail,                   -- :: ByteString -> ByteString
          init,                   -- :: ByteString -> ByteString
          null,                   -- :: ByteString -> Bool
          length,                 -- :: ByteString -> Int64
  
          -- * Transforming ByteStrings
          map,                    -- :: (Word8 -> Word8) -> ByteString -> ByteString
          reverse,                -- :: ByteString -> ByteString
          intersperse,            -- :: Word8 -> ByteString -> ByteString
          intercalate,            -- :: ByteString -> [ByteString] -> ByteString
          transpose,              -- :: [ByteString] -> [ByteString]
  
          -- * Reducing 'ByteString's (folds)
          foldl,                  -- :: (a -> Word8 -> a) -> a -> ByteString -> a
          foldl',                 -- :: (a -> Word8 -> a) -> a -> ByteString -> a
          foldl1,                 -- :: (Word8 -> Word8 -> Word8) -> ByteString -> Word8
          foldl1',                -- :: (Word8 -> Word8 -> Word8) -> ByteString -> Word8
          foldr,                  -- :: (Word8 -> a -> a) -> a -> ByteString -> a
          foldr1,                 -- :: (Word8 -> Word8 -> Word8) -> ByteString -> Word8
  
          -- ** Special folds
          concat,                 -- :: [ByteString] -> ByteString
          concatMap,              -- :: (Word8 -> ByteString) -> ByteString -> ByteString
          any,                    -- :: (Word8 -> Bool) -> ByteString -> Bool
          all,                    -- :: (Word8 -> Bool) -> ByteString -> Bool
          maximum,                -- :: ByteString -> Word8
          minimum,                -- :: ByteString -> Word8
  
          -- * Building ByteStrings
          -- ** Scans
          scanl,                  -- :: (Word8 -> Word8 -> Word8) -> Word8 -> ByteString -> ByteString
  --        scanl1,                 -- :: (Word8 -> Word8 -> Word8) -> ByteString -> ByteString
  --        scanr,                  -- :: (Word8 -> Word8 -> Word8) -> Word8 -> ByteString -> ByteString
  --        scanr1,                 -- :: (Word8 -> Word8 -> Word8) -> ByteString -> ByteString
  
          -- ** Accumulating maps
          mapAccumL,              -- :: (acc -> Word8 -> (acc, Word8)) -> acc -> ByteString -> (acc, ByteString)
          mapAccumR,              -- :: (acc -> Word8 -> (acc, Word8)) -> acc -> ByteString -> (acc, ByteString)
  
          -- ** Infinite ByteStrings
          repeat,                 -- :: Word8 -> ByteString
          replicate,              -- :: Int64 -> Word8 -> ByteString
          cycle,                  -- :: ByteString -> ByteString
          iterate,                -- :: (Word8 -> Word8) -> Word8 -> ByteString
  
          -- ** Unfolding ByteStrings
          unfoldr,                -- :: (a -> Maybe (Word8, a)) -> a -> ByteString
  
          -- * Substrings
  
          -- ** Breaking strings
          take,                   -- :: Int64 -> ByteString -> ByteString
          drop,                   -- :: Int64 -> ByteString -> ByteString
          splitAt,                -- :: Int64 -> ByteString -> (ByteString, ByteString)
          takeWhile,              -- :: (Word8 -> Bool) -> ByteString -> ByteString
          dropWhile,              -- :: (Word8 -> Bool) -> ByteString -> ByteString
          span,                   -- :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString)
          break,                  -- :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString)
          group,                  -- :: ByteString -> [ByteString]
          groupBy,                -- :: (Word8 -> Word8 -> Bool) -> ByteString -> [ByteString]
          inits,                  -- :: ByteString -> [ByteString]
          tails,                  -- :: ByteString -> [ByteString]
          stripPrefix,            -- :: ByteString -> ByteString -> Maybe ByteString
          stripSuffix,            -- :: ByteString -> ByteString -> Maybe ByteString
  
          -- ** Breaking into many substrings
          split,                  -- :: Word8 -> ByteString -> [ByteString]
          splitWith,              -- :: (Word8 -> Bool) -> ByteString -> [ByteString]
  
          -- * Predicates
          isPrefixOf,             -- :: ByteString -> ByteString -> Bool
          isSuffixOf,             -- :: ByteString -> ByteString -> Bool
  --        isInfixOf,              -- :: ByteString -> ByteString -> Bool
  
          -- ** Search for arbitrary substrings
  --        isSubstringOf,          -- :: ByteString -> ByteString -> Bool
  --        findSubstring,          -- :: ByteString -> ByteString -> Maybe Int
  --        findSubstrings,         -- :: ByteString -> ByteString -> [Int]
  
          -- * Searching ByteStrings
  
          -- ** Searching by equality
          elem,                   -- :: Word8 -> ByteString -> Bool
          notElem,                -- :: Word8 -> ByteString -> Bool
  
          -- ** Searching with a predicate
          find,                   -- :: (Word8 -> Bool) -> ByteString -> Maybe Word8
          filter,                 -- :: (Word8 -> Bool) -> ByteString -> ByteString
          partition,              -- :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString)
  
          -- * Indexing ByteStrings
          index,                  -- :: ByteString -> Int64 -> Word8
          elemIndex,              -- :: Word8 -> ByteString -> Maybe Int64
          elemIndexEnd,           -- :: Word8 -> ByteString -> Maybe Int64
          elemIndices,            -- :: Word8 -> ByteString -> [Int64]
          findIndex,              -- :: (Word8 -> Bool) -> ByteString -> Maybe Int64
          findIndices,            -- :: (Word8 -> Bool) -> ByteString -> [Int64]
          count,                  -- :: Word8 -> ByteString -> Int64
  
          -- * Zipping and unzipping ByteStrings
          zip,                    -- :: ByteString -> ByteString -> [(Word8,Word8)]
          zipWith,                -- :: (Word8 -> Word8 -> c) -> ByteString -> ByteString -> [c]
          unzip,                  -- :: [(Word8,Word8)] -> (ByteString,ByteString)
  
          -- * Ordered ByteStrings
  --        sort,                   -- :: ByteString -> ByteString
  
          -- * Low level conversions
          -- ** Copying ByteStrings
          copy,                   -- :: ByteString -> ByteString
  --        defrag,                -- :: ByteString -> ByteString
  
          -- * I\/O with 'ByteString's
  
          -- ** Standard input and output
          getContents,            -- :: IO ByteString
          putStr,                 -- :: ByteString -> IO ()
          putStrLn,               -- :: ByteString -> IO ()
          interact,               -- :: (ByteString -> ByteString) -> IO ()
  
          -- ** Files
          readFile,               -- :: FilePath -> IO ByteString
          writeFile,              -- :: FilePath -> ByteString -> IO ()
          appendFile,             -- :: FilePath -> ByteString -> IO ()
  
          -- ** I\/O with Handles
          hGetContents,           -- :: Handle -> IO ByteString
          hGet,                   -- :: Handle -> Int -> IO ByteString
          hGetNonBlocking,        -- :: Handle -> Int -> IO ByteString
          hPut,                   -- :: Handle -> ByteString -> IO ()
          hPutNonBlocking,        -- :: Handle -> ByteString -> IO ByteString
          hPutStr,                -- :: Handle -> ByteString -> IO ()
  
    ) where
  
  import Prelude hiding
      (reverse,head,tail,last,init,null,length,map,lines,foldl,foldr,unlines
      ,concat,any,take,drop,splitAt,takeWhile,dropWhile,span,break,elem,filter,maximum
      ,minimum,all,concatMap,foldl1,foldr1,scanl, scanl1, scanr, scanr1
      ,repeat, cycle, interact, iterate,readFile,writeFile,appendFile,replicate
      ,getContents,getLine,putStr,putStrLn ,zip,zipWith,unzip,notElem)
  
  import qualified Data.List              as L  -- L for list/lazy
  import qualified Data.ByteString        as P  (ByteString) -- type name only
  import qualified Data.ByteString        as S  -- S for strict (hmm...)
  import qualified Data.ByteString.Internal as S
  import qualified Data.ByteString.Unsafe as S
  import Data.ByteString.Lazy.Internal
  
  #if !(MIN_VERSION_base(4,8,0))
  import Control.Applicative      ((<$>))
  import Data.Monoid              (Monoid(..))
  #endif
  import Control.Monad            (mplus)
  import Data.Word                (Word8)
  import Data.Int                 (Int64)
  import System.IO                (Handle,openBinaryFile,stdin,stdout,withBinaryFile,IOMode(..)
                                  ,hClose)
  import System.IO.Error          (mkIOError, illegalOperationErrorType)
  import System.IO.Unsafe
  
  import Foreign.ForeignPtr       (withForeignPtr)
  import Foreign.Ptr
  import Foreign.Storable
  
  
  -- -----------------------------------------------------------------------------
  -- Introducing and eliminating 'ByteString's
  
  -- | /O(1)/ The empty 'ByteString'
  empty :: ByteString
  empty = Empty
  {-# INLINE empty #-}
  
  -- | /O(1)/ Convert a 'Word8' into a 'ByteString'
  singleton :: Word8 -> ByteString
  singleton w = Chunk (S.singleton w) Empty
  {-# INLINE singleton #-}
  
  -- | /O(n)/ Convert a '[Word8]' into a 'ByteString'.
  pack :: [Word8] -> ByteString
  pack = packBytes
  
  -- | /O(n)/ Converts a 'ByteString' to a '[Word8]'.
  unpack :: ByteString -> [Word8]
  unpack = unpackBytes
  
  -- | /O(c)/ Convert a list of strict 'ByteString' into a lazy 'ByteString'
  fromChunks :: [P.ByteString] -> ByteString
  fromChunks cs = L.foldr chunk Empty cs
  
  -- | /O(c)/ Convert a lazy 'ByteString' into a list of strict 'ByteString'
  toChunks :: ByteString -> [P.ByteString]
  toChunks cs = foldrChunks (:) [] cs
  
  -- |/O(1)/ Convert a strict 'ByteString' into a lazy 'ByteString'.
  fromStrict :: P.ByteString -> ByteString
  fromStrict bs | S.null bs = Empty
                | otherwise = Chunk bs Empty
  
  -- |/O(n)/ Convert a lazy 'ByteString' into a strict 'ByteString'.
  --
  -- Note that this is an /expensive/ operation that forces the whole lazy
  -- ByteString into memory and then copies all the data. If possible, try to
  -- avoid converting back and forth between strict and lazy bytestrings.
  --
  toStrict :: ByteString -> S.ByteString
  toStrict = \cs -> goLen0 cs cs
      -- We pass the original [ByteString] (bss0) through as an argument through
      -- goLen0, goLen1, and goLen since we will need it again in goCopy. Passing
      -- it as an explicit argument avoids capturing it in these functions'
      -- closures which would result in unnecessary closure allocation.
    where
      -- It's still possible that the result is empty
      goLen0 _   Empty                   = S.empty
      goLen0 cs0 (Chunk c cs) | S.null c = goLen0 cs0 cs
      goLen0 cs0 (Chunk c cs)            = goLen1 cs0 c cs
  
      -- It's still possible that the result is a single chunk
      goLen1 _   bs Empty                = bs
      goLen1 cs0 bs (Chunk c cs)
        | S.null c                   = goLen1 cs0 bs cs
        | otherwise                  =
          goLen cs0 (S.checkedAdd "Lazy.concat" (S.length bs) (S.length c)) cs
  
      -- General case, just find the total length we'll need
      goLen cs0 !total (Chunk c cs)      = goLen cs0 total' cs
        where
          total' = S.checkedAdd "Lazy.concat" total (S.length c)
      goLen cs0 total Empty =
        S.unsafeCreate total $ \ptr -> goCopy cs0 ptr
  
      -- Copy the data
      goCopy Empty                        !_   = return ()
      goCopy (Chunk (S.PS _  _   0  ) cs) !ptr = goCopy cs ptr
      goCopy (Chunk (S.PS fp off len) cs) !ptr = do
        withForeignPtr fp $ \p -> do
          S.memcpy ptr (p `plusPtr` off) len
          goCopy cs (ptr `plusPtr` len)
  -- See the comment on Data.ByteString.Internal.concat for some background on
  -- this implementation.
  
  ------------------------------------------------------------------------
  
  {-
  -- | /O(n)/ Convert a '[a]' into a 'ByteString' using some
  -- conversion function
  packWith :: (a -> Word8) -> [a] -> ByteString
  packWith k str = LPS $ L.map (P.packWith k) (chunk defaultChunkSize str)
  {-# INLINE packWith #-}
  {-# SPECIALIZE packWith :: (Char -> Word8) -> [Char] -> ByteString #-}
  
  -- | /O(n)/ Converts a 'ByteString' to a '[a]', using a conversion function.
  unpackWith :: (Word8 -> a) -> ByteString -> [a]
  unpackWith k (LPS ss) = L.concatMap (S.unpackWith k) ss
  {-# INLINE unpackWith #-}
  {-# SPECIALIZE unpackWith :: (Word8 -> Char) -> ByteString -> [Char] #-}
  -}
  
  -- ---------------------------------------------------------------------
  -- Basic interface
  
  -- | /O(1)/ Test whether a ByteString is empty.
  null :: ByteString -> Bool
  null Empty = True
  null _     = False
  {-# INLINE null #-}
  
  -- | /O(n\/c)/ 'length' returns the length of a ByteString as an 'Int64'
  length :: ByteString -> Int64
  length cs = foldlChunks (\n c -> n + fromIntegral (S.length c)) 0 cs
  {-# INLINE length #-}
  
  infixr 5 `cons`, `cons'` --same as list (:)
  infixl 5 `snoc`
  
  -- | /O(1)/ 'cons' is analogous to '(:)' for lists.
  --
  cons :: Word8 -> ByteString -> ByteString
  cons c cs = Chunk (S.singleton c) cs
  {-# INLINE cons #-}
  
  -- | /O(1)/ Unlike 'cons', 'cons'' is
  -- strict in the ByteString that we are consing onto. More precisely, it forces
  -- the head and the first chunk. It does this because, for space efficiency, it
  -- may coalesce the new byte onto the first \'chunk\' rather than starting a
  -- new \'chunk\'.
  --
  -- So that means you can't use a lazy recursive contruction like this:
  --
  -- > let xs = cons' c xs in xs
  --
  -- You can however use 'cons', as well as 'repeat' and 'cycle', to build
  -- infinite lazy ByteStrings.
  --
  cons' :: Word8 -> ByteString -> ByteString
  cons' w (Chunk c cs) | S.length c < 16 = Chunk (S.cons w c) cs
  cons' w cs                             = Chunk (S.singleton w) cs
  {-# INLINE cons' #-}
  
  -- | /O(n\/c)/ Append a byte to the end of a 'ByteString'
  snoc :: ByteString -> Word8 -> ByteString
  snoc cs w = foldrChunks Chunk (singleton w) cs
  {-# INLINE snoc #-}
  
  -- | /O(1)/ Extract the first element of a ByteString, which must be non-empty.
  head :: ByteString -> Word8
  head Empty       = errorEmptyList "head"
  head (Chunk c _) = S.unsafeHead c
  {-# INLINE head #-}
  
  -- | /O(1)/ Extract the head and tail of a ByteString, returning Nothing
  -- if it is empty.
  uncons :: ByteString -> Maybe (Word8, ByteString)
  uncons Empty = Nothing
  uncons (Chunk c cs)
      = Just (S.unsafeHead c,
              if S.length c == 1 then cs else Chunk (S.unsafeTail c) cs)
  {-# INLINE uncons #-}
  
  -- | /O(1)/ Extract the elements after the head of a ByteString, which must be
  -- non-empty.
  tail :: ByteString -> ByteString
  tail Empty          = errorEmptyList "tail"
  tail (Chunk c cs)
    | S.length c == 1 = cs
    | otherwise       = Chunk (S.unsafeTail c) cs
  {-# INLINE tail #-}
  
  -- | /O(n\/c)/ Extract the last element of a ByteString, which must be finite
  -- and non-empty.
  last :: ByteString -> Word8
  last Empty          = errorEmptyList "last"
  last (Chunk c0 cs0) = go c0 cs0
    where go c Empty        = S.unsafeLast c
          go _ (Chunk c cs) = go c cs
  -- XXX Don't inline this. Something breaks with 6.8.2 (haven't investigated yet)
  
  -- | /O(n\/c)/ Return all the elements of a 'ByteString' except the last one.
  init :: ByteString -> ByteString
  init Empty          = errorEmptyList "init"
  init (Chunk c0 cs0) = go c0 cs0
    where go c Empty | S.length c == 1 = Empty
                     | otherwise       = Chunk (S.unsafeInit c) Empty
          go c (Chunk c' cs)           = Chunk c (go c' cs)
  
  -- | /O(n\/c)/ Extract the 'init' and 'last' of a ByteString, returning Nothing
  -- if it is empty.
  --
  -- * It is no faster than using 'init' and 'last'
  unsnoc :: ByteString -> Maybe (ByteString, Word8)
  unsnoc Empty        = Nothing
  unsnoc (Chunk c cs) = Just (init (Chunk c cs), last (Chunk c cs))
  
  -- | /O(n\/c)/ Append two ByteStrings
  append :: ByteString -> ByteString -> ByteString
  append = mappend
  {-# INLINE append #-}
  
  -- ---------------------------------------------------------------------
  -- Transformations
  
  -- | /O(n)/ 'map' @f xs@ is the ByteString obtained by applying @f@ to each
  -- element of @xs@.
  map :: (Word8 -> Word8) -> ByteString -> ByteString
  map f s = go s
      where
          go Empty        = Empty
          go (Chunk x xs) = Chunk y ys
              where
                  y  = S.map f x
                  ys = go xs
  {-# INLINE map #-}
  
  -- | /O(n)/ 'reverse' @xs@ returns the elements of @xs@ in reverse order.
  reverse :: ByteString -> ByteString
  reverse cs0 = rev Empty cs0
    where rev a Empty        = a
          rev a (Chunk c cs) = rev (Chunk (S.reverse c) a) cs
  {-# INLINE reverse #-}
  
  -- | The 'intersperse' function takes a 'Word8' and a 'ByteString' and
  -- \`intersperses\' that byte between the elements of the 'ByteString'.
  -- It is analogous to the intersperse function on Lists.
  intersperse :: Word8 -> ByteString -> ByteString
  intersperse _ Empty        = Empty
  intersperse w (Chunk c cs) = Chunk (S.intersperse w c)
                                     (foldrChunks (Chunk . intersperse') Empty cs)
    where intersperse' :: P.ByteString -> P.ByteString
          intersperse' (S.PS fp o l) =
            S.unsafeCreate (2*l) $ \p' -> withForeignPtr fp $ \p -> do
              poke p' w
              S.c_intersperse (p' `plusPtr` 1) (p `plusPtr` o) (fromIntegral l) w
  
  -- | The 'transpose' function transposes the rows and columns of its
  -- 'ByteString' argument.
  transpose :: [ByteString] -> [ByteString]
  transpose css = L.map (\ss -> Chunk (S.pack ss) Empty)
                        (L.transpose (L.map unpack css))
  --TODO: make this fast
  
  -- ---------------------------------------------------------------------
  -- Reducing 'ByteString's
  
  -- | 'foldl', applied to a binary operator, a starting value (typically
  -- the left-identity of the operator), and a ByteString, reduces the
  -- ByteString using the binary operator, from left to right.
  foldl :: (a -> Word8 -> a) -> a -> ByteString -> a
  foldl f z = go z
    where go a Empty        = a
          go a (Chunk c cs) = go (S.foldl f a c) cs
  {-# INLINE foldl #-}
  
  -- | 'foldl'' is like 'foldl', but strict in the accumulator.
  foldl' :: (a -> Word8 -> a) -> a -> ByteString -> a
  foldl' f z = go z
    where go !a Empty        = a
          go !a (Chunk c cs) = go (S.foldl' f a c) cs
  {-# INLINE foldl' #-}
  
  -- | 'foldr', applied to a binary operator, a starting value
  -- (typically the right-identity of the operator), and a ByteString,
  -- reduces the ByteString using the binary operator, from right to left.
  foldr :: (Word8 -> a -> a) -> a -> ByteString -> a
  foldr k z = foldrChunks (flip (S.foldr k)) z
  {-# INLINE foldr #-}
  
  -- | 'foldl1' is a variant of 'foldl' that has no starting value
  -- argument, and thus must be applied to non-empty 'ByteStrings'.
  foldl1 :: (Word8 -> Word8 -> Word8) -> ByteString -> Word8
  foldl1 _ Empty        = errorEmptyList "foldl1"
  foldl1 f (Chunk c cs) = foldl f (S.unsafeHead c) (Chunk (S.unsafeTail c) cs)
  
  -- | 'foldl1'' is like 'foldl1', but strict in the accumulator.
  foldl1' :: (Word8 -> Word8 -> Word8) -> ByteString -> Word8
  foldl1' _ Empty        = errorEmptyList "foldl1'"
  foldl1' f (Chunk c cs) = foldl' f (S.unsafeHead c) (Chunk (S.unsafeTail c) cs)
  
  -- | 'foldr1' is a variant of 'foldr' that has no starting value argument,
  -- and thus must be applied to non-empty 'ByteString's
  foldr1 :: (Word8 -> Word8 -> Word8) -> ByteString -> Word8
  foldr1 _ Empty          = errorEmptyList "foldr1"
  foldr1 f (Chunk c0 cs0) = go c0 cs0
    where go c Empty         = S.foldr1 f c
          go c (Chunk c' cs) = S.foldr  f (go c' cs) c
  
  -- ---------------------------------------------------------------------
  -- Special folds
  
  -- | /O(n)/ Concatenate a list of ByteStrings.
  concat :: [ByteString] -> ByteString
  concat = mconcat
  
  -- | Map a function over a 'ByteString' and concatenate the results
  concatMap :: (Word8 -> ByteString) -> ByteString -> ByteString
  concatMap _ Empty        = Empty
  concatMap f (Chunk c0 cs0) = to c0 cs0
    where
      go :: ByteString -> P.ByteString -> ByteString -> ByteString
      go Empty        c' cs' = to c' cs'
      go (Chunk c cs) c' cs' = Chunk c (go cs c' cs')
  
      to :: P.ByteString -> ByteString -> ByteString
      to c cs | S.null c  = case cs of
          Empty          -> Empty
          (Chunk c' cs') -> to c' cs'
              | otherwise = go (f (S.unsafeHead c)) (S.unsafeTail c) cs
  
  -- | /O(n)/ Applied to a predicate and a ByteString, 'any' determines if
  -- any element of the 'ByteString' satisfies the predicate.
  any :: (Word8 -> Bool) -> ByteString -> Bool
  any f cs = foldrChunks (\c rest -> S.any f c || rest) False cs
  {-# INLINE any #-}
  -- todo fuse
  
  -- | /O(n)/ Applied to a predicate and a 'ByteString', 'all' determines
  -- if all elements of the 'ByteString' satisfy the predicate.
  all :: (Word8 -> Bool) -> ByteString -> Bool
  all f cs = foldrChunks (\c rest -> S.all f c && rest) True cs
  {-# INLINE all #-}
  -- todo fuse
  
  -- | /O(n)/ 'maximum' returns the maximum value from a 'ByteString'
  maximum :: ByteString -> Word8
  maximum Empty        = errorEmptyList "maximum"
  maximum (Chunk c cs) = foldlChunks (\n c' -> n `max` S.maximum c')
                                     (S.maximum c) cs
  {-# INLINE maximum #-}
  
  -- | /O(n)/ 'minimum' returns the minimum value from a 'ByteString'
  minimum :: ByteString -> Word8
  minimum Empty        = errorEmptyList "minimum"
  minimum (Chunk c cs) = foldlChunks (\n c' -> n `min` S.minimum c')
                                       (S.minimum c) cs
  {-# INLINE minimum #-}
  
  -- | The 'mapAccumL' function behaves like a combination of 'map' and
  -- 'foldl'; it applies a function to each element of a ByteString,
  -- passing an accumulating parameter from left to right, and returning a
  -- final value of this accumulator together with the new ByteString.
  mapAccumL :: (acc -> Word8 -> (acc, Word8)) -> acc -> ByteString -> (acc, ByteString)
  mapAccumL f s0 = go s0
    where
      go s Empty        = (s, Empty)
      go s (Chunk c cs) = (s'', Chunk c' cs')
          where (s',  c')  = S.mapAccumL f s c
                (s'', cs') = go s' cs
  
  -- | The 'mapAccumR' function behaves like a combination of 'map' and
  -- 'foldr'; it applies a function to each element of a ByteString,
  -- passing an accumulating parameter from right to left, and returning a
  -- final value of this accumulator together with the new ByteString.
  mapAccumR :: (acc -> Word8 -> (acc, Word8)) -> acc -> ByteString -> (acc, ByteString)
  mapAccumR f s0 = go s0
    where
      go s Empty        = (s, Empty)
      go s (Chunk c cs) = (s'', Chunk c' cs')
          where (s'', c') = S.mapAccumR f s' c
                (s', cs') = go s cs
  
  -- ---------------------------------------------------------------------
  -- Building ByteStrings
  
  -- | 'scanl' is similar to 'foldl', but returns a list of successive
  -- reduced values from the left. This function will fuse.
  --
  -- > scanl f z [x1, x2, ...] == [z, z `f` x1, (z `f` x1) `f` x2, ...]
  --
  -- Note that
  --
  -- > last (scanl f z xs) == foldl f z xs.
  scanl :: (Word8 -> Word8 -> Word8) -> Word8 -> ByteString -> ByteString
  scanl f z = snd . foldl k (z,singleton z)
   where
      k (c,acc) a = let n = f c a in (n, acc `snoc` n)
  {-# INLINE scanl #-}
  
  -- ---------------------------------------------------------------------
  -- Unfolds and replicates
  
  -- | @'iterate' f x@ returns an infinite ByteString of repeated applications
  -- of @f@ to @x@:
  --
  -- > iterate f x == [x, f x, f (f x), ...]
  --
  iterate :: (Word8 -> Word8) -> Word8 -> ByteString
  iterate f = unfoldr (\x -> case f x of !x' -> Just (x', x'))
  
  -- | @'repeat' x@ is an infinite ByteString, with @x@ the value of every
  -- element.
  --
  repeat :: Word8 -> ByteString
  repeat w = cs where cs = Chunk (S.replicate smallChunkSize w) cs
  
  -- | /O(n)/ @'replicate' n x@ is a ByteString of length @n@ with @x@
  -- the value of every element.
  --
  replicate :: Int64 -> Word8 -> ByteString
  replicate n w
      | n <= 0             = Empty
      | n < fromIntegral smallChunkSize = Chunk (S.replicate (fromIntegral n) w) Empty
      | r == 0             = cs -- preserve invariant
      | otherwise          = Chunk (S.unsafeTake (fromIntegral r) c) cs
   where
      c      = S.replicate smallChunkSize w
      cs     = nChunks q
      (q, r) = quotRem n (fromIntegral smallChunkSize)
      nChunks 0 = Empty
      nChunks m = Chunk c (nChunks (m-1))
  
  -- | 'cycle' ties a finite ByteString into a circular one, or equivalently,
  -- the infinite repetition of the original ByteString.
  --
  cycle :: ByteString -> ByteString
  cycle Empty = errorEmptyList "cycle"
  cycle cs    = cs' where cs' = foldrChunks Chunk cs' cs
  
  -- | /O(n)/ The 'unfoldr' function is analogous to the List \'unfoldr\'.
  -- 'unfoldr' builds a ByteString from a seed value.  The function takes
  -- the element and returns 'Nothing' if it is done producing the
  -- ByteString or returns 'Just' @(a,b)@, in which case, @a@ is a
  -- prepending to the ByteString and @b@ is used as the next element in a
  -- recursive call.
  unfoldr :: (a -> Maybe (Word8, a)) -> a -> ByteString
  unfoldr f z = unfoldChunk 32 z
    where unfoldChunk n x =
            case S.unfoldrN n f x of
              (c, Nothing)
                | S.null c  -> Empty
                | otherwise -> Chunk c Empty
              (c, Just x')  -> Chunk c (unfoldChunk (n*2) x')
  
  -- ---------------------------------------------------------------------
  -- Substrings
  
  -- | /O(n\/c)/ 'take' @n@, applied to a ByteString @xs@, returns the prefix
  -- of @xs@ of length @n@, or @xs@ itself if @n > 'length' xs@.
  take :: Int64 -> ByteString -> ByteString
  take i _ | i <= 0 = Empty
  take i cs0         = take' i cs0
    where take' 0 _            = Empty
          take' _ Empty        = Empty
          take' n (Chunk c cs) =
            if n < fromIntegral (S.length c)
              then Chunk (S.take (fromIntegral n) c) Empty
              else Chunk c (take' (n - fromIntegral (S.length c)) cs)
  
  -- | /O(n\/c)/ 'drop' @n xs@ returns the suffix of @xs@ after the first @n@
  -- elements, or @[]@ if @n > 'length' xs@.
  drop  :: Int64 -> ByteString -> ByteString
  drop i p | i <= 0 = p
  drop i cs0 = drop' i cs0
    where drop' 0 cs           = cs
          drop' _ Empty        = Empty
          drop' n (Chunk c cs) =
            if n < fromIntegral (S.length c)
              then Chunk (S.drop (fromIntegral n) c) cs
              else drop' (n - fromIntegral (S.length c)) cs
  
  -- | /O(n\/c)/ 'splitAt' @n xs@ is equivalent to @('take' n xs, 'drop' n xs)@.
  splitAt :: Int64 -> ByteString -> (ByteString, ByteString)
  splitAt i cs0 | i <= 0 = (Empty, cs0)
  splitAt i cs0 = splitAt' i cs0
    where splitAt' 0 cs           = (Empty, cs)
          splitAt' _ Empty        = (Empty, Empty)
          splitAt' n (Chunk c cs) =
            if n < fromIntegral (S.length c)
              then (Chunk (S.take (fromIntegral n) c) Empty
                   ,Chunk (S.drop (fromIntegral n) c) cs)
              else let (cs', cs'') = splitAt' (n - fromIntegral (S.length c)) cs
                     in (Chunk c cs', cs'')
  
  
  -- | 'takeWhile', applied to a predicate @p@ and a ByteString @xs@,
  -- returns the longest prefix (possibly empty) of @xs@ of elements that
  -- satisfy @p@.
  takeWhile :: (Word8 -> Bool) -> ByteString -> ByteString
  takeWhile f cs0 = takeWhile' cs0
    where takeWhile' Empty        = Empty
          takeWhile' (Chunk c cs) =
            case findIndexOrEnd (not . f) c of
              0                  -> Empty
              n | n < S.length c -> Chunk (S.take n c) Empty
                | otherwise      -> Chunk c (takeWhile' cs)
  
  -- | 'dropWhile' @p xs@ returns the suffix remaining after 'takeWhile' @p xs@.
  dropWhile :: (Word8 -> Bool) -> ByteString -> ByteString
  dropWhile f cs0 = dropWhile' cs0
    where dropWhile' Empty        = Empty
          dropWhile' (Chunk c cs) =
            case findIndexOrEnd (not . f) c of
              n | n < S.length c -> Chunk (S.drop n c) cs
                | otherwise      -> dropWhile' cs
  
  -- | 'break' @p@ is equivalent to @'span' ('not' . p)@.
  break :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString)
  break f cs0 = break' cs0
    where break' Empty        = (Empty, Empty)
          break' (Chunk c cs) =
            case findIndexOrEnd f c of
              0                  -> (Empty, Chunk c cs)
              n | n < S.length c -> (Chunk (S.take n c) Empty
                                    ,Chunk (S.drop n c) cs)
                | otherwise      -> let (cs', cs'') = break' cs
                                     in (Chunk c cs', cs'')
  
  --
  -- TODO
  --
  -- Add rules
  --
  
  {-
  -- | 'breakByte' breaks its ByteString argument at the first occurence
  -- of the specified byte. It is more efficient than 'break' as it is
  -- implemented with @memchr(3)@. I.e.
  --
  -- > break (=='c') "abcd" == breakByte 'c' "abcd"
  --
  breakByte :: Word8 -> ByteString -> (ByteString, ByteString)
  breakByte c (LPS ps) = case (breakByte' ps) of (a,b) -> (LPS a, LPS b)
    where breakByte' []     = ([], [])
          breakByte' (x:xs) =
            case P.elemIndex c x of
              Just 0  -> ([], x : xs)
              Just n  -> (P.take n x : [], P.drop n x : xs)
              Nothing -> let (xs', xs'') = breakByte' xs
                          in (x : xs', xs'')
  
  -- | 'spanByte' breaks its ByteString argument at the first
  -- occurence of a byte other than its argument. It is more efficient
  -- than 'span (==)'
  --
  -- > span  (=='c') "abcd" == spanByte 'c' "abcd"
  --
  spanByte :: Word8 -> ByteString -> (ByteString, ByteString)
  spanByte c (LPS ps) = case (spanByte' ps) of (a,b) -> (LPS a, LPS b)
    where spanByte' []     = ([], [])
          spanByte' (x:xs) =
            case P.spanByte c x of
              (x', x'') | P.null x'  -> ([], x : xs)
                        | P.null x'' -> let (xs', xs'') = spanByte' xs
                                         in (x : xs', xs'')
                        | otherwise  -> (x' : [], x'' : xs)
  -}
  
  -- | 'span' @p xs@ breaks the ByteString into two segments. It is
  -- equivalent to @('takeWhile' p xs, 'dropWhile' p xs)@
  span :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString)
  span p = break (not . p)
  
  -- | /O(n)/ Splits a 'ByteString' into components delimited by
  -- separators, where the predicate returns True for a separator element.
  -- The resulting components do not contain the separators.  Two adjacent
  -- separators result in an empty component in the output.  eg.
  --
  -- > splitWith (=='a') "aabbaca" == ["","","bb","c",""]
  -- > splitWith (=='a') []        == []
  --
  splitWith :: (Word8 -> Bool) -> ByteString -> [ByteString]
  splitWith _ Empty          = []
  splitWith p (Chunk c0 cs0) = comb [] (S.splitWith p c0) cs0
  
    where comb :: [P.ByteString] -> [P.ByteString] -> ByteString -> [ByteString]
          comb acc (s:[]) Empty        = revChunks (s:acc) : []
          comb acc (s:[]) (Chunk c cs) = comb (s:acc) (S.splitWith p c) cs
          comb acc (s:ss) cs           = revChunks (s:acc) : comb [] ss cs
  {-# INLINE splitWith #-}
  
  -- | /O(n)/ Break a 'ByteString' into pieces separated by the byte
  -- argument, consuming the delimiter. I.e.
  --
  -- > split '\n' "a\nb\nd\ne" == ["a","b","d","e"]
  -- > split 'a'  "aXaXaXa"    == ["","X","X","X",""]
  -- > split 'x'  "x"          == ["",""]
  --
  -- and
  --
  -- > intercalate [c] . split c == id
  -- > split == splitWith . (==)
  --
  -- As for all splitting functions in this library, this function does
  -- not copy the substrings, it just constructs new 'ByteStrings' that
  -- are slices of the original.
  --
  split :: Word8 -> ByteString -> [ByteString]
  split _ Empty     = []
  split w (Chunk c0 cs0) = comb [] (S.split w c0) cs0
  
    where comb :: [P.ByteString] -> [P.ByteString] -> ByteString -> [ByteString]
          comb acc (s:[]) Empty        = revChunks (s:acc) : []
          comb acc (s:[]) (Chunk c cs) = comb (s:acc) (S.split w c) cs
          comb acc (s:ss) cs        = revChunks (s:acc) : comb [] ss cs
  {-# INLINE split #-}
  
  -- | The 'group' function takes a ByteString and returns a list of
  -- ByteStrings such that the concatenation of the result is equal to the
  -- argument.  Moreover, each sublist in the result contains only equal
  -- elements.  For example,
  --
  -- > group "Mississippi" = ["M","i","ss","i","ss","i","pp","i"]
  --
  -- It is a special case of 'groupBy', which allows the programmer to
  -- supply their own equality test.
  group :: ByteString -> [ByteString]
  group = go
    where
      go Empty        = []
      go (Chunk c cs)
        | S.length c == 1  = to [c] (S.unsafeHead c) cs
        | otherwise        = to [S.unsafeTake 1 c] (S.unsafeHead c) (Chunk (S.unsafeTail c) cs)
  
      to acc !_ Empty        = revNonEmptyChunks acc : []
      to acc !w (Chunk c cs) =
        case findIndexOrEnd (/= w) c of
          0                    -> revNonEmptyChunks acc
                                : go (Chunk c cs)
          n | n == S.length c  -> to (S.unsafeTake n c : acc) w cs
            | otherwise        -> revNonEmptyChunks (S.unsafeTake n c : acc)
                                : go (Chunk (S.unsafeDrop n c) cs)
  
  -- | The 'groupBy' function is the non-overloaded version of 'group'.
  --
  groupBy :: (Word8 -> Word8 -> Bool) -> ByteString -> [ByteString]
  groupBy k = go
    where
      go Empty        = []
      go (Chunk c cs)
        | S.length c == 1  = to [c] (S.unsafeHead c) cs
        | otherwise        = to [S.unsafeTake 1 c] (S.unsafeHead c) (Chunk (S.unsafeTail c) cs)
  
      to acc !_ Empty        = revNonEmptyChunks acc : []
      to acc !w (Chunk c cs) =
        case findIndexOrEnd (not . k w) c of
          0                    -> revNonEmptyChunks acc
                                : go (Chunk c cs)
          n | n == S.length c  -> to (S.unsafeTake n c : acc) w cs
            | otherwise        -> revNonEmptyChunks (S.unsafeTake n c : acc)
                                : go (Chunk (S.unsafeDrop n c) cs)
  
  -- | /O(n)/ The 'intercalate' function takes a 'ByteString' and a list of
  -- 'ByteString's and concatenates the list after interspersing the first
  -- argument between each element of the list.
  intercalate :: ByteString -> [ByteString] -> ByteString
  intercalate s = concat . L.intersperse s
  
  -- ---------------------------------------------------------------------
  -- Indexing ByteStrings
  
  -- | /O(c)/ 'ByteString' index (subscript) operator, starting from 0.
  index :: ByteString -> Int64 -> Word8
  index _  i | i < 0  = moduleError "index" ("negative index: " ++ show i)
  index cs0 i         = index' cs0 i
    where index' Empty     n = moduleError "index" ("index too large: " ++ show n)
          index' (Chunk c cs) n
            | n >= fromIntegral (S.length c) =
                index' cs (n - fromIntegral (S.length c))
            | otherwise       = S.unsafeIndex c (fromIntegral n)
  
  -- | /O(n)/ The 'elemIndex' function returns the index of the first
  -- element in the given 'ByteString' which is equal to the query
  -- element, or 'Nothing' if there is no such element.
  -- This implementation uses memchr(3).
  elemIndex :: Word8 -> ByteString -> Maybe Int64
  elemIndex w cs0 = elemIndex' 0 cs0
    where elemIndex' _ Empty        = Nothing
          elemIndex' n (Chunk c cs) =
            case S.elemIndex w c of
              Nothing -> elemIndex' (n + fromIntegral (S.length c)) cs
              Just i  -> Just (n + fromIntegral i)
  
  -- | /O(n)/ The 'elemIndexEnd' function returns the last index of the
  -- element in the given 'ByteString' which is equal to the query
  -- element, or 'Nothing' if there is no such element. The following
  -- holds:
  --
  -- > elemIndexEnd c xs ==
  -- > (-) (length xs - 1) `fmap` elemIndex c (reverse xs)
  --
  -- @since 0.10.6.0
  elemIndexEnd :: Word8 -> ByteString -> Maybe Int64
  elemIndexEnd w = elemIndexEnd' 0
    where
      elemIndexEnd' _ Empty = Nothing
      elemIndexEnd' n (Chunk c cs) =
        let !n' = n + S.length c
            !i  = fmap (fromIntegral . (n +)) $ S.elemIndexEnd w c
        in elemIndexEnd' n' cs `mplus` i
  
  -- | /O(n)/ The 'elemIndices' function extends 'elemIndex', by returning
  -- the indices of all elements equal to the query element, in ascending order.
  -- This implementation uses memchr(3).
  elemIndices :: Word8 -> ByteString -> [Int64]
  elemIndices w cs0 = elemIndices' 0 cs0
    where elemIndices' _ Empty        = []
          elemIndices' n (Chunk c cs) = L.map ((+n).fromIntegral) (S.elemIndices w c)
                               ++ elemIndices' (n + fromIntegral (S.length c)) cs
  
  -- | count returns the number of times its argument appears in the ByteString
  --
  -- > count = length . elemIndices
  --
  -- But more efficiently than using length on the intermediate list.
  count :: Word8 -> ByteString -> Int64
  count w cs = foldlChunks (\n c -> n + fromIntegral (S.count w c)) 0 cs
  
  -- | The 'findIndex' function takes a predicate and a 'ByteString' and
  -- returns the index of the first element in the ByteString
  -- satisfying the predicate.
  findIndex :: (Word8 -> Bool) -> ByteString -> Maybe Int64
  findIndex k cs0 = findIndex' 0 cs0
    where findIndex' _ Empty        = Nothing
          findIndex' n (Chunk c cs) =
            case S.findIndex k c of
              Nothing -> findIndex' (n + fromIntegral (S.length c)) cs
              Just i  -> Just (n + fromIntegral i)
  {-# INLINE findIndex #-}
  
  -- | /O(n)/ The 'find' function takes a predicate and a ByteString,
  -- and returns the first element in matching the predicate, or 'Nothing'
  -- if there is no such element.
  --
  -- > find f p = case findIndex f p of Just n -> Just (p ! n) ; _ -> Nothing
  --
  find :: (Word8 -> Bool) -> ByteString -> Maybe Word8
  find f cs0 = find' cs0
    where find' Empty        = Nothing
          find' (Chunk c cs) = case S.find f c of
              Nothing -> find' cs
              Just w  -> Just w
  {-# INLINE find #-}
  
  -- | The 'findIndices' function extends 'findIndex', by returning the
  -- indices of all elements satisfying the predicate, in ascending order.
  findIndices :: (Word8 -> Bool) -> ByteString -> [Int64]
  findIndices k cs0 = findIndices' 0 cs0
    where findIndices' _ Empty        = []
          findIndices' n (Chunk c cs) = L.map ((+n).fromIntegral) (S.findIndices k c)
                               ++ findIndices' (n + fromIntegral (S.length c)) cs
  
  -- ---------------------------------------------------------------------
  -- Searching ByteStrings
  
  -- | /O(n)/ 'elem' is the 'ByteString' membership predicate.
  elem :: Word8 -> ByteString -> Bool
  elem w cs = case elemIndex w cs of Nothing -> False ; _ -> True
  
  -- | /O(n)/ 'notElem' is the inverse of 'elem'
  notElem :: Word8 -> ByteString -> Bool
  notElem w cs = not (elem w cs)
  
  -- | /O(n)/ 'filter', applied to a predicate and a ByteString,
  -- returns a ByteString containing those characters that satisfy the
  -- predicate.
  filter :: (Word8 -> Bool) -> ByteString -> ByteString
  filter p s = go s
      where
          go Empty        = Empty
          go (Chunk x xs) = chunk (S.filter p x) (go xs)
  {-# INLINE filter #-}
  
  {-
  -- | /O(n)/ and /O(n\/c) space/ A first order equivalent of /filter .
  -- (==)/, for the common case of filtering a single byte. It is more
  -- efficient to use /filterByte/ in this case.
  --
  -- > filterByte == filter . (==)
  --
  -- filterByte is around 10x faster, and uses much less space, than its
  -- filter equivalent
  filterByte :: Word8 -> ByteString -> ByteString
  filterByte w ps = replicate (count w ps) w
  {-# INLINE filterByte #-}
  
  {-# RULES
  "ByteString specialise filter (== x)" forall x.
    filter ((==) x) = filterByte x
  
  "ByteString specialise filter (== x)" forall x.
   filter (== x) = filterByte x
    #-}
  -}
  
  {-
  -- | /O(n)/ A first order equivalent of /filter . (\/=)/, for the common
  -- case of filtering a single byte out of a list. It is more efficient
  -- to use /filterNotByte/ in this case.
  --
  -- > filterNotByte == filter . (/=)
  --
  -- filterNotByte is around 2x faster than its filter equivalent.
  filterNotByte :: Word8 -> ByteString -> ByteString
  filterNotByte w (LPS xs) = LPS (filterMap (P.filterNotByte w) xs)
  -}
  
  -- | /O(n)/ The 'partition' function takes a predicate a ByteString and returns
  -- the pair of ByteStrings with elements which do and do not satisfy the
  -- predicate, respectively; i.e.,
  --
  -- > partition p bs == (filter p xs, filter (not . p) xs)
  --
  partition :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString)
  partition _ Empty = (Empty, Empty)
  partition p (Chunk x xs) = (chunk t ts, chunk f fs)
    where
      (t,   f) = S.partition p x
      (ts, fs) = partition   p xs
  
  -- ---------------------------------------------------------------------
  -- Searching for substrings
  
  -- | /O(n)/ The 'isPrefixOf' function takes two ByteStrings and returns 'True'
  -- iff the first is a prefix of the second.
  isPrefixOf :: ByteString -> ByteString -> Bool
  isPrefixOf Empty _  = True
  isPrefixOf _ Empty  = False
  isPrefixOf (Chunk x xs) (Chunk y ys)
      | S.length x == S.length y = x == y  && isPrefixOf xs ys
      | S.length x <  S.length y = x == yh && isPrefixOf xs (Chunk yt ys)
      | otherwise                = xh == y && isPrefixOf (Chunk xt xs) ys
    where (xh,xt) = S.splitAt (S.length y) x
          (yh,yt) = S.splitAt (S.length x) y
  
  -- | /O(n)/ The 'stripPrefix' function takes two ByteStrings and returns 'Just'
  -- the remainder of the second iff the first is its prefix, and otherwise
  -- 'Nothing'.
  --
  -- @since 0.10.8.0
  stripPrefix :: ByteString -> ByteString -> Maybe ByteString
  stripPrefix Empty bs  = Just bs
  stripPrefix _ Empty  = Nothing
  stripPrefix (Chunk x xs) (Chunk y ys)
      | S.length x == S.length y = if x == y then stripPrefix xs ys else Nothing
      | S.length x <  S.length y = do yt <- S.stripPrefix x y
                                      stripPrefix xs (Chunk yt ys)
      | otherwise                = do xt <- S.stripPrefix y x
                                      stripPrefix (Chunk xt xs) ys
  
  -- | /O(n)/ The 'isSuffixOf' function takes two ByteStrings and returns 'True'
  -- iff the first is a suffix of the second.
  --
  -- The following holds:
  --
  -- > isSuffixOf x y == reverse x `isPrefixOf` reverse y
  --
  isSuffixOf :: ByteString -> ByteString -> Bool
  isSuffixOf x y = reverse x `isPrefixOf` reverse y
  --TODO: a better implementation
  
  -- | /O(n)/ The 'stripSuffix' function takes two ByteStrings and returns 'Just'
  -- the remainder of the second iff the first is its suffix, and otherwise
  -- 'Nothing'.
  stripSuffix :: ByteString -> ByteString -> Maybe ByteString
  stripSuffix x y = reverse <$> stripPrefix (reverse x) (reverse y)
  --TODO: a better implementation
  
  -- ---------------------------------------------------------------------
  -- Zipping
  
  -- | /O(n)/ 'zip' takes two ByteStrings and returns a list of
  -- corresponding pairs of bytes. If one input ByteString is short,
  -- excess elements of the longer ByteString are discarded. This is
  -- equivalent to a pair of 'unpack' operations.
  zip :: ByteString -> ByteString -> [(Word8,Word8)]
  zip = zipWith (,)
  
  -- | 'zipWith' generalises 'zip' by zipping with the function given as
  -- the first argument, instead of a tupling function.  For example,
  -- @'zipWith' (+)@ is applied to two ByteStrings to produce the list of
  -- corresponding sums.
  zipWith :: (Word8 -> Word8 -> a) -> ByteString -> ByteString -> [a]
  zipWith _ Empty     _  = []
  zipWith _ _      Empty = []
  zipWith f (Chunk a as) (Chunk b bs) = go a as b bs
    where
      go x xs y ys = f (S.unsafeHead x) (S.unsafeHead y)
                   : to (S.unsafeTail x) xs (S.unsafeTail y) ys
  
      to x Empty         _ _             | S.null x       = []
      to _ _             y Empty         | S.null y       = []
      to x xs            y ys            | not (S.null x)
                                        && not (S.null y) = go x  xs y  ys
      to x xs            _ (Chunk y' ys) | not (S.null x) = go x  xs y' ys
      to _ (Chunk x' xs) y ys            | not (S.null y) = go x' xs y  ys
      to _ (Chunk x' xs) _ (Chunk y' ys)                  = go x' xs y' ys
  
  -- | /O(n)/ 'unzip' transforms a list of pairs of bytes into a pair of
  -- ByteStrings. Note that this performs two 'pack' operations.
  unzip :: [(Word8,Word8)] -> (ByteString,ByteString)
  unzip ls = (pack (L.map fst ls), pack (L.map snd ls))
  {-# INLINE unzip #-}
  
  -- ---------------------------------------------------------------------
  -- Special lists
  
  -- | /O(n)/ Return all initial segments of the given 'ByteString', shortest first.
  inits :: ByteString -> [ByteString]
  inits = (Empty :) . inits'
    where inits' Empty        = []
          inits' (Chunk c cs) = L.map (`Chunk` Empty) (L.tail (S.inits c))
                             ++ L.map (Chunk c) (inits' cs)
  
  -- | /O(n)/ Return all final segments of the given 'ByteString', longest first.
  tails :: ByteString -> [ByteString]
  tails Empty         = Empty : []
  tails cs@(Chunk c cs')
    | S.length c == 1 = cs : tails cs'
    | otherwise       = cs : tails (Chunk (S.unsafeTail c) cs')
  
  -- ---------------------------------------------------------------------
  -- Low level constructors
  
  -- | /O(n)/ Make a copy of the 'ByteString' with its own storage.
  --   This is mainly useful to allow the rest of the data pointed
  --   to by the 'ByteString' to be garbage collected, for example
  --   if a large string has been read in, and only a small part of it
  --   is needed in the rest of the program.
  copy :: ByteString -> ByteString
  copy cs = foldrChunks (Chunk . S.copy) Empty cs
  --TODO, we could coalese small blocks here
  --FIXME: probably not strict enough, if we're doing this to avoid retaining
  -- the parent blocks then we'd better copy strictly.
  
  -- ---------------------------------------------------------------------
  
  -- TODO defrag func that concatenates block together that are below a threshold
  -- defrag :: ByteString -> ByteString
  
  -- ---------------------------------------------------------------------
  -- Lazy ByteString IO
  --
  -- Rule for when to close: is it expected to read the whole file?
  -- If so, close when done.
  --
  
  -- | Read entire handle contents /lazily/ into a 'ByteString'. Chunks
  -- are read on demand, in at most @k@-sized chunks. It does not block
  -- waiting for a whole @k@-sized chunk, so if less than @k@ bytes are
  -- available then they will be returned immediately as a smaller chunk.
  --
  -- The handle is closed on EOF.
  --
  -- Note: the 'Handle' should be placed in binary mode with
  -- 'System.IO.hSetBinaryMode' for 'hGetContentsN' to
  -- work correctly.
  --
  hGetContentsN :: Int -> Handle -> IO ByteString
  hGetContentsN k h = lazyRead -- TODO close on exceptions
    where
      lazyRead = unsafeInterleaveIO loop
  
      loop = do
          c <- S.hGetSome h k -- only blocks if there is no data available
          if S.null c
            then hClose h >> return Empty
            else do cs <- lazyRead
                    return (Chunk c cs)
  
  -- | Read @n@ bytes into a 'ByteString', directly from the
  -- specified 'Handle', in chunks of size @k@.
  --
  hGetN :: Int -> Handle -> Int -> IO ByteString
  hGetN k h n | n > 0 = readChunks n
    where
      readChunks !i = do
          c <- S.hGet h (min k i)
          case S.length c of
              0 -> return Empty
              m -> do cs <- readChunks (i - m)
                      return (Chunk c cs)
  
  hGetN _ _ 0 = return Empty
  hGetN _ h n = illegalBufferSize h "hGet" n
  
  -- | hGetNonBlockingN is similar to 'hGetContentsN', except that it will never block
  -- waiting for data to become available, instead it returns only whatever data
  -- is available. Chunks are read on demand, in @k@-sized chunks.
  --
  hGetNonBlockingN :: Int -> Handle -> Int -> IO ByteString
  hGetNonBlockingN k h n | n > 0= readChunks n
    where
      readChunks !i = do
          c <- S.hGetNonBlocking h (min k i)
          case S.length c of
              0 -> return Empty
              m -> do cs <- readChunks (i - m)
                      return (Chunk c cs)
  
  hGetNonBlockingN _ _ 0 = return Empty
  hGetNonBlockingN _ h n = illegalBufferSize h "hGetNonBlocking" n
  
  illegalBufferSize :: Handle -> String -> Int -> IO a
  illegalBufferSize handle fn sz =
      ioError (mkIOError illegalOperationErrorType msg (Just handle) Nothing)
      --TODO: System.IO uses InvalidArgument here, but it's not exported :-(
      where
        msg = fn ++ ": illegal ByteString size " ++ showsPrec 9 sz []
  
  -- | Read entire handle contents /lazily/ into a 'ByteString'. Chunks
  -- are read on demand, using the default chunk size.
  --
  -- Once EOF is encountered, the Handle is closed.
  --
  -- Note: the 'Handle' should be placed in binary mode with
  -- 'System.IO.hSetBinaryMode' for 'hGetContents' to
  -- work correctly.
  --
  hGetContents :: Handle -> IO ByteString
  hGetContents = hGetContentsN defaultChunkSize
  
  -- | Read @n@ bytes into a 'ByteString', directly from the specified 'Handle'.
  --
  hGet :: Handle -> Int -> IO ByteString
  hGet = hGetN defaultChunkSize
  
  -- | hGetNonBlocking is similar to 'hGet', except that it will never block
  -- waiting for data to become available, instead it returns only whatever data
  -- is available.  If there is no data available to be read, 'hGetNonBlocking'
  -- returns 'empty'.
  --
  -- Note: on Windows and with Haskell implementation other than GHC, this
  -- function does not work correctly; it behaves identically to 'hGet'.
  --
  hGetNonBlocking :: Handle -> Int -> IO ByteString
  hGetNonBlocking = hGetNonBlockingN defaultChunkSize
  
  -- | Read an entire file /lazily/ into a 'ByteString'.
  -- The Handle will be held open until EOF is encountered.
  --
  readFile :: FilePath -> IO ByteString
  readFile f = openBinaryFile f ReadMode >>= hGetContents
  
  modifyFile :: IOMode -> FilePath -> ByteString -> IO ()
  modifyFile mode f txt = withBinaryFile f mode (`hPut` txt)
  
  -- | Write a 'ByteString' to a file.
  --
  writeFile :: FilePath -> ByteString -> IO ()
  writeFile = modifyFile WriteMode
  
  -- | Append a 'ByteString' to a file.
  --
  appendFile :: FilePath -> ByteString -> IO ()
  appendFile = modifyFile AppendMode
  
  -- | getContents. Equivalent to hGetContents stdin. Will read /lazily/
  --
  getContents :: IO ByteString
  getContents = hGetContents stdin
  
  -- | Outputs a 'ByteString' to the specified 'Handle'. The chunks will be
  -- written one at a time. Other threads might write to the 'Handle' between the
  -- writes, and hence 'hPut' alone might not be suitable for concurrent writes.
  --
  hPut :: Handle -> ByteString -> IO ()
  hPut h cs = foldrChunks (\c rest -> S.hPut h c >> rest) (return ()) cs
  
  -- | Similar to 'hPut' except that it will never block. Instead it returns
  -- any tail that did not get written. This tail may be 'empty' in the case that
  -- the whole string was written, or the whole original string if nothing was
  -- written. Partial writes are also possible.
  --
  -- Note: on Windows and with Haskell implementation other than GHC, this
  -- function does not work correctly; it behaves identically to 'hPut'.
  --
  hPutNonBlocking :: Handle -> ByteString -> IO ByteString
  hPutNonBlocking _ Empty           = return Empty
  hPutNonBlocking h bs@(Chunk c cs) = do
    c' <- S.hPutNonBlocking h c
    case S.length c' of
      l' | l' == S.length c -> hPutNonBlocking h cs
      0                     -> return bs
      _                     -> return (Chunk c' cs)
  
  -- | A synonym for @hPut@, for compatibility
  --
  hPutStr :: Handle -> ByteString -> IO ()
  hPutStr = hPut
  
  -- | Write a ByteString to stdout
  putStr :: ByteString -> IO ()
  putStr = hPut stdout
  
  -- | Write a ByteString to stdout, appending a newline byte
  --
  putStrLn :: ByteString -> IO ()
  putStrLn ps = hPut stdout ps >> hPut stdout (singleton 0x0a)
  
  {-# DEPRECATED putStrLn
      "Use Data.ByteString.Lazy.Char8.putStrLn instead. (Functions that rely on ASCII encodings belong in Data.ByteString.Lazy.Char8)"
    #-}
  
  -- | The interact function takes a function of type @ByteString -> ByteString@
  -- as its argument. The entire input from the standard input device is passed
  -- to this function as its argument, and the resulting string is output on the
  -- standard output device.
  --
  interact :: (ByteString -> ByteString) -> IO ()
  interact transformer = putStr . transformer =<< getContents
  
  -- ---------------------------------------------------------------------
  -- Internal utilities
  
  -- Common up near identical calls to `error' to reduce the number
  -- constant strings created when compiled:
  errorEmptyList :: String -> a
  errorEmptyList fun = moduleError fun "empty ByteString"
  {-# NOINLINE errorEmptyList #-}
  
  moduleError :: String -> String -> a
  moduleError fun msg = error ("Data.ByteString.Lazy." ++ fun ++ ':':' ':msg)
  {-# NOINLINE moduleError #-}
  
  
  -- reverse a list of non-empty chunks into a lazy ByteString
  revNonEmptyChunks :: [P.ByteString] -> ByteString
  revNonEmptyChunks cs = L.foldl' (flip Chunk) Empty cs
  
  -- reverse a list of possibly-empty chunks into a lazy ByteString
  revChunks :: [P.ByteString] -> ByteString
  revChunks cs = L.foldl' (flip chunk) Empty cs
  
  -- | 'findIndexOrEnd' is a variant of findIndex, that returns the length
  -- of the string if no element is found, rather than Nothing.
  findIndexOrEnd :: (Word8 -> Bool) -> P.ByteString -> Int
  findIndexOrEnd k (S.PS x s l) =
      S.accursedUnutterablePerformIO $
        withForeignPtr x $ \f -> go (f `plusPtr` s) 0
    where
      go !ptr !n | n >= l    = return l
                 | otherwise = do w <- peek ptr
                                  if k w
                                    then return n
                                    else go (ptr `plusPtr` 1) (n+1)
  {-# INLINE findIndexOrEnd #-}
  