Data/ByteString/Lazy/Char8.hs

    {-# LANGUAGE CPP, BangPatterns #-}
    {-# OPTIONS_HADDOCK prune #-}
    #if __GLASGOW_HASKELL__ >= 701
    {-# LANGUAGE Trustworthy #-}
    #endif

    -- |
    -- Module      : Data.ByteString.Lazy.Char8
    -- Copyright   : (c) Don Stewart 2006-2008
    --               (c) Duncan Coutts 2006-2011
    -- License     : BSD-style
    --
    -- Maintainer  : dons00@gmail.com, duncan@community.haskell.org
    -- Stability   : stable
    -- Portability : portable
    --
    -- Manipulate /lazy/ 'ByteString's using 'Char' operations. All Chars will
    -- be truncated to 8 bits. It can be expected that these functions will
    -- run at identical speeds to their 'Data.Word.Word8' equivalents in
    -- "Data.ByteString.Lazy".
    --
    -- This module is intended to be imported @qualified@, to avoid name
    -- clashes with "Prelude" functions.  eg.
    --
    -- > import qualified Data.ByteString.Lazy.Char8 as C
    --
    -- The Char8 interface to bytestrings provides an instance of IsString
    -- for the ByteString type, enabling you to use string literals, and
    -- have them implicitly packed to ByteStrings.
    -- Use @{-\# LANGUAGE OverloadedStrings \#-}@ to enable this.
    --

    module Data.ByteString.Lazy.Char8 (

            -- * The @ByteString@ type
            ByteString,             -- instances: Eq, Ord, Show, Read, Data, Typeable

            -- * Introducing and eliminating 'ByteString's
            empty,                  -- :: ByteString
            singleton,              -- :: Char   -> ByteString
            pack,                   -- :: String -> ByteString
            unpack,                 -- :: ByteString -> String
            fromChunks,             -- :: [Strict.ByteString] -> ByteString
            toChunks,               -- :: ByteString -> [Strict.ByteString]
            fromStrict,             -- :: Strict.ByteString -> ByteString
            toStrict,               -- :: ByteString -> Strict.ByteString

            -- * Basic interface
            cons,                   -- :: Char -> ByteString -> ByteString
            cons',                  -- :: Char -> ByteString -> ByteString
            snoc,                   -- :: ByteString -> Char -> ByteString
            append,                 -- :: ByteString -> ByteString -> ByteString
            head,                   -- :: ByteString -> Char
            uncons,                 -- :: ByteString -> Maybe (Char, ByteString)
            last,                   -- :: ByteString -> Char
            tail,                   -- :: ByteString -> ByteString
            unsnoc,                 -- :: ByteString -> Maybe (ByteString, Char)
            init,                   -- :: ByteString -> ByteString
            null,                   -- :: ByteString -> Bool
            length,                 -- :: ByteString -> Int64

            -- * Transforming ByteStrings
            map,                    -- :: (Char -> Char) -> ByteString -> ByteString
            reverse,                -- :: ByteString -> ByteString
            intersperse,            -- :: Char -> ByteString -> ByteString
            intercalate,            -- :: ByteString -> [ByteString] -> ByteString
            transpose,              -- :: [ByteString] -> [ByteString]

            -- * Reducing 'ByteString's (folds)
            foldl,                  -- :: (a -> Char -> a) -> a -> ByteString -> a
            foldl',                 -- :: (a -> Char -> a) -> a -> ByteString -> a
            foldl1,                 -- :: (Char -> Char -> Char) -> ByteString -> Char
            foldl1',                -- :: (Char -> Char -> Char) -> ByteString -> Char
            foldr,                  -- :: (Char -> a -> a) -> a -> ByteString -> a
            foldr1,                 -- :: (Char -> Char -> Char) -> ByteString -> Char

            -- ** Special folds
            concat,                 -- :: [ByteString] -> ByteString
            concatMap,              -- :: (Char -> ByteString) -> ByteString -> ByteString
            any,                    -- :: (Char -> Bool) -> ByteString -> Bool
            all,                    -- :: (Char -> Bool) -> ByteString -> Bool
            maximum,                -- :: ByteString -> Char
            minimum,                -- :: ByteString -> Char

            -- * Building ByteStrings
            -- ** Scans
            scanl,                  -- :: (Char -> Char -> Char) -> Char -> ByteString -> ByteString
    --      scanl1,                 -- :: (Char -> Char -> Char) -> ByteString -> ByteString
    --      scanr,                  -- :: (Char -> Char -> Char) -> Char -> ByteString -> ByteString
    --      scanr1,                 -- :: (Char -> Char -> Char) -> ByteString -> ByteString

            -- ** Accumulating maps
            mapAccumL,              -- :: (acc -> Char -> (acc, Char)) -> acc -> ByteString -> (acc, ByteString)
            mapAccumR,              -- :: (acc -> Char -> (acc, Char)) -> acc -> ByteString -> (acc, ByteString)

            -- ** Infinite ByteStrings
            repeat,                 -- :: Char -> ByteString
            replicate,              -- :: Int64 -> Char -> ByteString
            cycle,                  -- :: ByteString -> ByteString
            iterate,                -- :: (Char -> Char) -> Char -> ByteString

            -- ** Unfolding ByteStrings
            unfoldr,                -- :: (a -> Maybe (Char, a)) -> a -> ByteString

            -- * Substrings

            -- ** Breaking strings
            take,                   -- :: Int64 -> ByteString -> ByteString
            drop,                   -- :: Int64 -> ByteString -> ByteString
            splitAt,                -- :: Int64 -> ByteString -> (ByteString, ByteString)
            takeWhile,              -- :: (Char -> Bool) -> ByteString -> ByteString
            dropWhile,              -- :: (Char -> Bool) -> ByteString -> ByteString
            span,                   -- :: (Char -> Bool) -> ByteString -> (ByteString, ByteString)
            break,                  -- :: (Char -> Bool) -> ByteString -> (ByteString, ByteString)
            group,                  -- :: ByteString -> [ByteString]
            groupBy,                -- :: (Char -> Char -> Bool) -> ByteString -> [ByteString]
            inits,                  -- :: ByteString -> [ByteString]
            tails,                  -- :: ByteString -> [ByteString]
            stripPrefix,            -- :: ByteString -> ByteString -> Maybe ByteString
            stripSuffix,            -- :: ByteString -> ByteString -> Maybe ByteString

            -- ** Breaking into many substrings
            split,                  -- :: Char -> ByteString -> [ByteString]
            splitWith,              -- :: (Char -> Bool) -> ByteString -> [ByteString]

            -- ** Breaking into lines and words
            lines,                  -- :: ByteString -> [ByteString]
            words,                  -- :: ByteString -> [ByteString]
            unlines,                -- :: [ByteString] -> ByteString
            unwords,                -- :: ByteString -> [ByteString]

            -- * Predicates
            isPrefixOf,             -- :: ByteString -> ByteString -> Bool
            isSuffixOf,             -- :: ByteString -> ByteString -> Bool

            -- * Searching ByteStrings

            -- ** Searching by equality
            elem,                   -- :: Char -> ByteString -> Bool
            notElem,                -- :: Char -> ByteString -> Bool

            -- ** Searching with a predicate
            find,                   -- :: (Char -> Bool) -> ByteString -> Maybe Char
            filter,                 -- :: (Char -> Bool) -> ByteString -> ByteString
    --      partition               -- :: (Char -> Bool) -> ByteString -> (ByteString, ByteString)

            -- * Indexing ByteStrings
            index,                  -- :: ByteString -> Int64 -> Char
            elemIndex,              -- :: Char -> ByteString -> Maybe Int64
            elemIndices,            -- :: Char -> ByteString -> [Int64]
            findIndex,              -- :: (Char -> Bool) -> ByteString -> Maybe Int64
            findIndices,            -- :: (Char -> Bool) -> ByteString -> [Int64]
            count,                  -- :: Char -> ByteString -> Int64

            -- * Zipping and unzipping ByteStrings
            zip,                    -- :: ByteString -> ByteString -> [(Char,Char)]
            zipWith,                -- :: (Char -> Char -> c) -> ByteString -> ByteString -> [c]
    --      unzip,                  -- :: [(Char,Char)] -> (ByteString,ByteString)

            -- * Ordered ByteStrings
    --        sort,                   -- :: ByteString -> ByteString

            -- * Low level conversions
            -- ** Copying ByteStrings
            copy,                   -- :: ByteString -> ByteString

            -- * Reading from ByteStrings
            readInt,
            readInteger,

            -- * I\/O with 'ByteString's
            -- | ByteString I/O uses binary mode, without any character decoding
            -- or newline conversion. The fact that it does not respect the Handle
            -- newline mode is considered a flaw and may be changed in a future version.

            -- ** 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 -> Int64 -> IO ByteString
            hGetNonBlocking,        -- :: Handle -> Int64 -> IO ByteString
            hPut,                   -- :: Handle -> ByteString -> IO ()
            hPutNonBlocking,        -- :: Handle -> ByteString -> IO ByteString
            hPutStr,                -- :: Handle -> ByteString -> IO ()
            hPutStrLn,              -- :: Handle -> ByteString -> IO ()

      ) where

    -- Functions transparently exported
    import Data.ByteString.Lazy
            (fromChunks, toChunks, fromStrict, toStrict
            ,empty,null,length,tail,init,append,reverse,transpose,cycle
            ,concat,take,drop,splitAt,intercalate
            ,isPrefixOf,isSuffixOf,group,inits,tails,copy
            ,stripPrefix,stripSuffix
            ,hGetContents, hGet, hPut, getContents
            ,hGetNonBlocking, hPutNonBlocking
            ,putStr, hPutStr, interact
            ,readFile,writeFile,appendFile)

    -- Functions we need to wrap.
    import qualified Data.ByteString.Lazy as L
    import qualified Data.ByteString as S (ByteString) -- typename only
    import qualified Data.ByteString as B
    import qualified Data.ByteString.Unsafe as B
    import Data.ByteString.Lazy.Internal

    import Data.ByteString.Internal (w2c, c2w, isSpaceWord8)

    import Data.Int (Int64)
    import qualified Data.List as List

    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
            ,unwords,words,maximum,minimum,all,concatMap,scanl,scanl1,foldl1,foldr1
            ,readFile,writeFile,appendFile,replicate,getContents,getLine,putStr,putStrLn
            ,zip,zipWith,unzip,notElem,repeat,iterate,interact,cycle)

    import System.IO            (Handle, stdout)

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

    -- | /O(1)/ Convert a 'Char' into a 'ByteString'
    singleton :: Char -> ByteString
    singleton = L.singleton . c2w
    {-# INLINE singleton #-}

    -- | /O(n)/ Convert a 'String' into a 'ByteString'.
    pack :: [Char] -> ByteString
    pack = packChars

    -- | /O(n)/ Converts a 'ByteString' to a 'String'.
    unpack :: ByteString -> [Char]
    unpack = unpackChars

    infixr 5 `cons`, `cons'` --same as list (:)
    infixl 5 `snoc`

    -- | /O(1)/ 'cons' is analogous to '(:)' for lists.
    cons :: Char -> ByteString -> ByteString
    cons = L.cons . c2w
    {-# 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' :: Char -> ByteString -> ByteString
    cons' = L.cons' . c2w
    {-# INLINE cons' #-}

    -- | /O(n)/ Append a Char to the end of a 'ByteString'. Similar to
    -- 'cons', this function performs a memcpy.
    snoc :: ByteString -> Char -> ByteString
    snoc p = L.snoc p . c2w
    {-# INLINE snoc #-}

    -- | /O(1)/ Extract the first element of a ByteString, which must be non-empty.
    head :: ByteString -> Char
    head = w2c . L.head
    {-# INLINE head #-}

    -- | /O(1)/ Extract the head and tail of a ByteString, returning Nothing
    -- if it is empty.
    uncons :: ByteString -> Maybe (Char, ByteString)
    uncons bs = case L.uncons bs of
                      Nothing -> Nothing
                      Just (w, bs') -> Just (w2c w, bs')
    {-# INLINE uncons #-}

    -- | /O(n\/c)/ Extract the 'init' and 'last' of a ByteString, returning Nothing
    -- if it is empty.
    unsnoc :: ByteString -> Maybe (ByteString, Char)
    unsnoc bs = case L.unsnoc bs of
                      Nothing -> Nothing
                      Just (bs', w) -> Just (bs', w2c w)
    {-# INLINE unsnoc #-}

    -- | /O(1)/ Extract the last element of a packed string, which must be non-empty.
    last :: ByteString -> Char
    last = w2c . L.last
    {-# INLINE last #-}

    -- | /O(n)/ 'map' @f xs@ is the ByteString obtained by applying @f@ to each element of @xs@
    map :: (Char -> Char) -> ByteString -> ByteString
    map f = L.map (c2w . f . w2c)
    {-# INLINE map #-}

    -- | /O(n)/ The 'intersperse' function takes a Char and a 'ByteString'
    -- and \`intersperses\' that Char between the elements of the
    -- 'ByteString'.  It is analogous to the intersperse function on Lists.
    intersperse :: Char -> ByteString -> ByteString
    intersperse = L.intersperse . c2w
    {-# INLINE intersperse #-}

    -- | '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 -> Char -> a) -> a -> ByteString -> a
    foldl f = L.foldl (\a c -> f a (w2c c))
    {-# INLINE foldl #-}

    -- | 'foldl\'' is like foldl, but strict in the accumulator.
    foldl' :: (a -> Char -> a) -> a -> ByteString -> a
    foldl' f = L.foldl' (\a c -> f a (w2c c))
    {-# INLINE foldl' #-}

    -- | 'foldr', applied to a binary operator, a starting value
    -- (typically the right-identity of the operator), and a packed string,
    -- reduces the packed string using the binary operator, from right to left.
    foldr :: (Char -> a -> a) -> a -> ByteString -> a
    foldr f = L.foldr (\c a -> f (w2c c) a)
    {-# INLINE foldr #-}

    -- | 'foldl1' is a variant of 'foldl' that has no starting value
    -- argument, and thus must be applied to non-empty 'ByteStrings'.
    foldl1 :: (Char -> Char -> Char) -> ByteString -> Char
    foldl1 f ps = w2c (L.foldl1 (\x y -> c2w (f (w2c x) (w2c y))) ps)
    {-# INLINE foldl1 #-}

    -- | 'foldl1\'' is like 'foldl1', but strict in the accumulator.
    foldl1' :: (Char -> Char -> Char) -> ByteString -> Char
    foldl1' f ps = w2c (L.foldl1' (\x y -> c2w (f (w2c x) (w2c y))) ps)

    -- | 'foldr1' is a variant of 'foldr' that has no starting value argument,
    -- and thus must be applied to non-empty 'ByteString's
    foldr1 :: (Char -> Char -> Char) -> ByteString -> Char
    foldr1 f ps = w2c (L.foldr1 (\x y -> c2w (f (w2c x) (w2c y))) ps)
    {-# INLINE foldr1 #-}

    -- | Map a function over a 'ByteString' and concatenate the results
    concatMap :: (Char -> ByteString) -> ByteString -> ByteString
    concatMap f = L.concatMap (f . w2c)
    {-# INLINE concatMap #-}

    -- | Applied to a predicate and a ByteString, 'any' determines if
    -- any element of the 'ByteString' satisfies the predicate.
    any :: (Char -> Bool) -> ByteString -> Bool
    any f = L.any (f . w2c)
    {-# INLINE any #-}

    -- | Applied to a predicate and a 'ByteString', 'all' determines if
    -- all elements of the 'ByteString' satisfy the predicate.
    all :: (Char -> Bool) -> ByteString -> Bool
    all f = L.all (f . w2c)
    {-# INLINE all #-}

    -- | 'maximum' returns the maximum value from a 'ByteString'
    maximum :: ByteString -> Char
    maximum = w2c . L.maximum
    {-# INLINE maximum #-}

    -- | 'minimum' returns the minimum value from a 'ByteString'
    minimum :: ByteString -> Char
    minimum = w2c . L.minimum
    {-# INLINE minimum #-}

    -- ---------------------------------------------------------------------
    -- 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 :: (Char -> Char -> Char) -> Char -> ByteString -> ByteString
    scanl f z = L.scanl (\a b -> c2w (f (w2c a) (w2c b))) (c2w z)

    -- | 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 -> Char -> (acc, Char)) -> acc -> ByteString -> (acc, ByteString)
    mapAccumL f = L.mapAccumL (\a w -> case f a (w2c w) of (a',c) -> (a', c2w c))

    -- | 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 -> Char -> (acc, Char)) -> acc -> ByteString -> (acc, ByteString)
    mapAccumR f = L.mapAccumR (\acc w -> case f acc (w2c w) of (acc', c) -> (acc', c2w c))

    ------------------------------------------------------------------------
    -- Generating and unfolding ByteStrings

    -- | @'iterate' f x@ returns an infinite ByteString of repeated applications
    -- of @f@ to @x@:
    --
    -- > iterate f x == [x, f x, f (f x), ...]
    --
    iterate :: (Char -> Char) -> Char -> ByteString
    iterate f = L.iterate (c2w . f . w2c) . c2w

    -- | @'repeat' x@ is an infinite ByteString, with @x@ the value of every
    -- element.
    --
    repeat :: Char -> ByteString
    repeat = L.repeat . c2w

    -- | /O(n)/ @'replicate' n x@ is a ByteString of length @n@ with @x@
    -- the value of every element.
    --
    replicate :: Int64 -> Char -> ByteString
    replicate w c = L.replicate w (c2w c)

    -- | /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 (Char, a)) -> a -> ByteString
    unfoldr f = L.unfoldr $ \a -> case f a of
                                        Nothing      -> Nothing
                                        Just (c, a') -> Just (c2w c, a')

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

    -- | 'takeWhile', applied to a predicate @p@ and a ByteString @xs@,
    -- returns the longest prefix (possibly empty) of @xs@ of elements that
    -- satisfy @p@.
    takeWhile :: (Char -> Bool) -> ByteString -> ByteString
    takeWhile f = L.takeWhile (f . w2c)
    {-# INLINE takeWhile #-}

    -- | 'dropWhile' @p xs@ returns the suffix remaining after 'takeWhile' @p xs@.
    dropWhile :: (Char -> Bool) -> ByteString -> ByteString
    dropWhile f = L.dropWhile (f . w2c)
    {-# INLINE dropWhile #-}

    -- | 'break' @p@ is equivalent to @'span' ('not' . p)@.
    break :: (Char -> Bool) -> ByteString -> (ByteString, ByteString)
    break f = L.break (f . w2c)
    {-# INLINE break #-}

    -- | 'span' @p xs@ breaks the ByteString into two segments. It is
    -- equivalent to @('takeWhile' p xs, 'dropWhile' p xs)@
    span :: (Char -> Bool) -> ByteString -> (ByteString, ByteString)
    span f = L.span (f . w2c)
    {-# INLINE span #-}

    {-
    -- | 'breakChar' breaks its ByteString argument at the first occurence
    -- of the specified Char. It is more efficient than 'break' as it is
    -- implemented with @memchr(3)@. I.e.
    --
    -- > break (=='c') "abcd" == breakChar 'c' "abcd"
    --
    breakChar :: Char -> ByteString -> (ByteString, ByteString)
    breakChar = L.breakByte . c2w
    {-# INLINE breakChar #-}

    -- | 'spanChar' breaks its ByteString argument at the first
    -- occurence of a Char other than its argument. It is more efficient
    -- than 'span (==)'
    --
    -- > span  (=='c') "abcd" == spanByte 'c' "abcd"
    --
    spanChar :: Char -> ByteString -> (ByteString, ByteString)
    spanChar = L.spanByte . c2w
    {-# INLINE spanChar #-}
    -}

    --
    -- TODO, more rules for breakChar*
    --

    -- | /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 :: Char -> ByteString -> [ByteString]
    split = L.split . c2w
    {-# INLINE split #-}

    -- | /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 :: (Char -> Bool) -> ByteString -> [ByteString]
    splitWith f = L.splitWith (f . w2c)
    {-# INLINE splitWith #-}

    -- | The 'groupBy' function is the non-overloaded version of 'group'.
    groupBy :: (Char -> Char -> Bool) -> ByteString -> [ByteString]
    groupBy k = L.groupBy (\a b -> k (w2c a) (w2c b))

    -- | /O(1)/ 'ByteString' index (subscript) operator, starting from 0.
    index :: ByteString -> Int64 -> Char
    index = (w2c .) . L.index
    {-# INLINE index #-}

    -- | /O(n)/ The 'elemIndex' function returns the index of the first
    -- element in the given 'ByteString' which is equal (by memchr) to the
    -- query element, or 'Nothing' if there is no such element.
    elemIndex :: Char -> ByteString -> Maybe Int64
    elemIndex = L.elemIndex . c2w
    {-# INLINE elemIndex #-}

    -- | /O(n)/ The 'elemIndices' function extends 'elemIndex', by returning
    -- the indices of all elements equal to the query element, in ascending order.
    elemIndices :: Char -> ByteString -> [Int64]
    elemIndices = L.elemIndices . c2w
    {-# INLINE elemIndices #-}

    -- | The 'findIndex' function takes a predicate and a 'ByteString' and
    -- returns the index of the first element in the ByteString satisfying the predicate.
    findIndex :: (Char -> Bool) -> ByteString -> Maybe Int64
    findIndex f = L.findIndex (f . w2c)
    {-# INLINE findIndex #-}

    -- | The 'findIndices' function extends 'findIndex', by returning the
    -- indices of all elements satisfying the predicate, in ascending order.
    findIndices :: (Char -> Bool) -> ByteString -> [Int64]
    findIndices f = L.findIndices (f . w2c)

    -- | count returns the number of times its argument appears in the ByteString
    --
    -- > count      == length . elemIndices
    -- > count '\n' == length . lines
    --
    -- But more efficiently than using length on the intermediate list.
    count :: Char -> ByteString -> Int64
    count c = L.count (c2w c)

    -- | /O(n)/ 'elem' is the 'ByteString' membership predicate. This
    -- implementation uses @memchr(3)@.
    elem :: Char -> ByteString -> Bool
    elem c = L.elem (c2w c)
    {-# INLINE elem #-}

    -- | /O(n)/ 'notElem' is the inverse of 'elem'
    notElem :: Char -> ByteString -> Bool
    notElem c = L.notElem (c2w c)
    {-# INLINE notElem #-}

    -- | /O(n)/ 'filter', applied to a predicate and a ByteString,
    -- returns a ByteString containing those characters that satisfy the
    -- predicate.
    filter :: (Char -> Bool) -> ByteString -> ByteString
    filter f = L.filter (f . w2c)
    {-# INLINE filter #-}

    {-
    -- | /O(n)/ and /O(n\/c) space/ A first order equivalent of /filter .
    -- (==)/, for the common case of filtering a single Char. It is more
    -- efficient to use /filterChar/ in this case.
    --
    -- > filterChar == filter . (==)
    --
    -- filterChar is around 10x faster, and uses much less space, than its
    -- filter equivalent
    --
    filterChar :: Char -> ByteString -> ByteString
    filterChar c ps = replicate (count c ps) c
    {-# INLINE filterChar #-}

    {-# RULES
      "ByteString specialise filter (== x)" forall x.
          filter ((==) x) = filterChar x
      #-}

    {-# RULES
      "ByteString specialise filter (== x)" forall x.
         filter (== x) = filterChar x
      #-}
    -}

    -- | /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 :: (Char -> Bool) -> ByteString -> Maybe Char
    find f ps = w2c `fmap` L.find (f . w2c) ps
    {-# INLINE find #-}

    {-
    -- | /O(n)/ A first order equivalent of /filter . (==)/, for the common
    -- case of filtering a single Char. It is more efficient to use
    -- filterChar in this case.
    --
    -- > filterChar == filter . (==)
    --
    -- filterChar is around 10x faster, and uses much less space, than its
    -- filter equivalent
    --
    filterChar :: Char -> ByteString -> ByteString
    filterChar c = L.filterByte (c2w c)
    {-# INLINE filterChar #-}

    -- | /O(n)/ A first order equivalent of /filter . (\/=)/, for the common
    -- case of filtering a single Char out of a list. It is more efficient
    -- to use /filterNotChar/ in this case.
    --
    -- > filterNotChar == filter . (/=)
    --
    -- filterNotChar is around 3x faster, and uses much less space, than its
    -- filter equivalent
    --
    filterNotChar :: Char -> ByteString -> ByteString
    filterNotChar c = L.filterNotByte (c2w c)
    {-# INLINE filterNotChar #-}
    -}

    -- | /O(n)/ 'zip' takes two ByteStrings and returns a list of
    -- corresponding pairs of Chars. If one input ByteString is short,
    -- excess elements of the longer ByteString are discarded. This is
    -- equivalent to a pair of 'unpack' operations, and so space
    -- usage may be large for multi-megabyte ByteStrings
    zip :: ByteString -> ByteString -> [(Char,Char)]
    zip ps qs
        | L.null ps || L.null qs = []
        | otherwise = (head ps, head qs) : zip (L.tail ps) (L.tail qs)

    -- | '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 :: (Char -> Char -> a) -> ByteString -> ByteString -> [a]
    zipWith f = L.zipWith ((. w2c) . f . w2c)

    -- | 'lines' breaks a ByteString up into a list of ByteStrings at
    -- newline Chars. The resulting strings do not contain newlines.
    --
    -- As of bytestring 0.9.0.3, this function is stricter than its
    -- list cousin.
    --
    lines :: ByteString -> [ByteString]
    lines Empty          = []
    lines (Chunk c0 cs0) = loop0 c0 cs0
        where
        -- this is a really performance sensitive function but the
        -- chunked representation makes the general case a bit expensive
        -- however assuming a large chunk size and normalish line lengths
        -- we will find line endings much more frequently than chunk
        -- endings so it makes sense to optimise for that common case.
        -- So we partition into two special cases depending on whether we
        -- are keeping back a list of chunks that will eventually be output
        -- once we get to the end of the current line.

        -- the common special case where we have no existing chunks of
        -- the current line
        loop0 :: S.ByteString -> ByteString -> [ByteString]
        loop0 c cs =
            case B.elemIndex (c2w '\n') c of
                Nothing -> case cs of
                               Empty  | B.null c  ->                 []
                                      | otherwise -> Chunk c Empty : []
                               (Chunk c' cs')
                                   | B.null c  -> loop0 c'     cs'
                                   | otherwise -> loop  c' [c] cs'

                Just n | n /= 0    -> Chunk (B.unsafeTake n c) Empty
                                    : loop0 (B.unsafeDrop (n+1) c) cs
                       | otherwise -> Empty
                                    : loop0 (B.unsafeTail c) cs

        -- the general case when we are building a list of chunks that are
        -- part of the same line
        loop :: S.ByteString -> [S.ByteString] -> ByteString -> [ByteString]
        loop c line cs =
            case B.elemIndex (c2w '\n') c of
                Nothing ->
                    case cs of
                        Empty -> let c' = revChunks (c : line)
                                  in c' `seq` (c' : [])

                        (Chunk c' cs') -> loop c' (c : line) cs'

                Just n ->
                    let c' = revChunks (B.unsafeTake n c : line)
                     in c' `seq` (c' : loop0 (B.unsafeDrop (n+1) c) cs)

    {-

    This function is too strict!  Consider,

    > prop_lazy =
        (L.unpack . head . lazylines $ L.append (L.pack "a\nb\n") (error "failed"))
      ==
        "a"

    fails.  Here's a properly lazy version of 'lines' for lazy bytestrings

        lazylines           :: L.ByteString -> [L.ByteString]
        lazylines s
            | L.null s  = []
            | otherwise =
                let (l,s') = L.break ((==) '\n') s
                in l : if L.null s' then []
                                    else lazylines (L.tail s')

    we need a similarly lazy, but efficient version.

    -}

    -- | 'unlines' is an inverse operation to 'lines'.  It joins lines,
    -- after appending a terminating newline to each.
    unlines :: [ByteString] -> ByteString
    unlines [] = empty
    unlines ss = concat (List.intersperse nl ss) `append` nl -- half as much space
        where nl = singleton '\n'

    -- | 'words' breaks a ByteString up into a list of words, which
    -- were delimited by Chars representing white space. And
    --
    -- > tokens isSpace = words
    --
    words :: ByteString -> [ByteString]
    words = List.filter (not . L.null) . L.splitWith isSpaceWord8
    {-# INLINE words #-}

    -- | The 'unwords' function is analogous to the 'unlines' function, on words.
    unwords :: [ByteString] -> ByteString
    unwords = intercalate (singleton ' ')
    {-# INLINE unwords #-}

    -- | readInt reads an Int from the beginning of the ByteString.  If
    -- there is no integer at the beginning of the string, it returns
    -- Nothing, otherwise it just returns the int read, and the rest of the
    -- string.

    readInt :: ByteString -> Maybe (Int, ByteString)
    {-# INLINE readInt #-}
    readInt Empty        = Nothing
    readInt (Chunk x xs) = case w2c (B.unsafeHead x) of
        '-' -> loop True  0 0 (B.unsafeTail x) xs
        '+' -> loop False 0 0 (B.unsafeTail x) xs
        _   -> loop False 0 0 x xs

        where loop :: Bool -> Int -> Int
                    -> S.ByteString -> ByteString -> Maybe (Int, ByteString)
              loop neg !i !n !c cs
                  | B.null c = case cs of
                                 Empty          -> end  neg i n c  cs
                                 (Chunk c' cs') -> loop neg i n c' cs'
                  | otherwise =
                      case B.unsafeHead c of
                        w | w >= 0x30
                         && w <= 0x39 -> loop neg (i+1)
                                              (n * 10 + (fromIntegral w - 0x30))
                                              (B.unsafeTail c) cs
                          | otherwise -> end neg i n c cs

              {-# INLINE end #-}
              end _   0 _ _  _ = Nothing
              end neg _ n c cs = e
                    where n' = if neg then negate n else n
                          c' = chunk c cs
                          e  = n' `seq` c' `seq` Just (n',c')
             --                  in n' `seq` c' `seq` JustS n' c'

    -- | readInteger reads an Integer from the beginning of the ByteString.  If
    -- there is no integer at the beginning of the string, it returns Nothing,
    -- otherwise it just returns the int read, and the rest of the string.
    readInteger :: ByteString -> Maybe (Integer, ByteString)
    readInteger Empty = Nothing
    readInteger (Chunk c0 cs0) =
            case w2c (B.unsafeHead c0) of
                '-' -> first (B.unsafeTail c0) cs0 >>= \(n, cs') -> return (-n, cs')
                '+' -> first (B.unsafeTail c0) cs0
                _   -> first c0 cs0

        where first c cs
                  | B.null c = case cs of
                      Empty          -> Nothing
                      (Chunk c' cs') -> first' c' cs'
                  | otherwise = first' c cs

              first' c cs = case B.unsafeHead c of
                  w | w >= 0x30 && w <= 0x39 -> Just $
                      loop 1 (fromIntegral w - 0x30) [] (B.unsafeTail c) cs
                    | otherwise              -> Nothing

              loop :: Int -> Int -> [Integer]
                   -> S.ByteString -> ByteString -> (Integer, ByteString)
              loop !d !acc ns !c cs
                  | B.null c = case cs of
                                 Empty          -> combine d acc ns c cs
                                 (Chunk c' cs') -> loop d acc ns c' cs'
                  | otherwise =
                      case B.unsafeHead c of
                       w | w >= 0x30 && w <= 0x39 ->
                           if d < 9 then loop (d+1)
                                              (10*acc + (fromIntegral w - 0x30))
                                              ns (B.unsafeTail c) cs
                                    else loop 1 (fromIntegral w - 0x30)
                                              (fromIntegral acc : ns)
                                              (B.unsafeTail c) cs
                         | otherwise -> combine d acc ns c cs

              combine _ acc [] c cs = end (fromIntegral acc) c cs
              combine d acc ns c cs =
                  end (10^d * combine1 1000000000 ns + fromIntegral acc) c cs

              combine1 _ [n] = n
              combine1 b ns  = combine1 (b*b) $ combine2 b ns

              combine2 b (n:m:ns) = let t = n+m*b in t `seq` (t : combine2 b ns)
              combine2 _ ns       = ns

              end n c cs = let c' = chunk c cs
                            in c' `seq` (n, c')

    -- | Write a ByteString to a handle, appending a newline byte
    --
    hPutStrLn :: Handle -> ByteString -> IO ()
    hPutStrLn h ps = hPut h ps >> hPut h (L.singleton 0x0a)

    -- | Write a ByteString to stdout, appending a newline byte
    --
    putStrLn :: ByteString -> IO ()
    putStrLn = hPutStrLn stdout

    -- ---------------------------------------------------------------------
    -- Internal utilities

    -- reverse a list of possibly-empty chunks into a lazy ByteString
    revChunks :: [S.ByteString] -> ByteString
    revChunks cs = List.foldl' (flip chunk) Empty cs