bytestring-0.10.4.0: Fast, compact, strict and lazy byte strings with a list interface

Copyright | (c) The University of Glasgow 2001, (c) David Roundy 2003-2005, (c) Simon Marlow 2005, (c) Bjorn Bringert 2006, (c) Don Stewart 2005-2008, (c) Duncan Coutts 2006-2013
License | BSD-style
Maintainer | dons00@gmail.com, duncan@community.haskell.org
Stability | stable
Portability | portable
Safe Haskell | Trustworthy
Language | Haskell98

Data.ByteString

Contents

- The `ByteString` type
- Introducing and eliminating `ByteString`s
- Basic interface
- Transforming ByteStrings
- Reducing `ByteString`s (folds)
  - Special folds
- Building ByteStrings
  - Scans
  - Accumulating maps
  - Generating and unfolding ByteStrings
- Substrings
  - Breaking strings
  - Breaking into many substrings
- Predicates
  - Search for arbitrary substrings
- Searching ByteStrings
  - Searching by equality
  - Searching with a predicate
- Indexing ByteStrings
- Zipping and unzipping ByteStrings
- Ordered ByteStrings
- Low level conversions
  - Copying ByteStrings
  - Packing `CString`s and pointers
  - Using ByteStrings as `CString`s
- I/O with `ByteString`s
  - Standard input and output
  - Files
  - I/O with Handles

Description

A time and space-efficient implementation of byte vectors using packed Word8 arrays, suitable for high performance use, both in terms of large data quantities, or high speed requirements. Byte vectors are encoded as strict `Word8` arrays of bytes, held in a `ForeignPtr`, and can be passed between C and Haskell with little effort.

The recomended way to assemble 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 as B

Original GHC implementation by Bryan O'Sullivan. Rewritten to use `UArray` by Simon Marlow. Rewritten to support slices and use `ForeignPtr` by David Roundy. Rewritten again and extended by Don Stewart and Duncan Coutts.

Synopsis

- data ByteString
- empty :: ByteString
- singleton :: Word8 -> ByteString
- pack :: [Word8] -> ByteString
- unpack :: ByteString -> [Word8]
- 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 -> Int
- map :: (Word8 -> Word8) -> ByteString -> ByteString
- reverse :: ByteString -> ByteString
- intersperse :: Word8 -> ByteString -> ByteString
- intercalate :: ByteString -> [ByteString] -> ByteString
- transpose :: [ByteString] -> [ByteString]
- 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
- foldr' :: (Word8 -> a -> a) -> a -> ByteString -> a
- foldr1 :: (Word8 -> Word8 -> Word8) -> ByteString -> Word8
- foldr1' :: (Word8 -> Word8 -> Word8) -> ByteString -> Word8
- concat :: [ByteString] -> ByteString
- concatMap :: (Word8 -> ByteString) -> ByteString -> ByteString
- any :: (Word8 -> Bool) -> ByteString -> Bool
- all :: (Word8 -> Bool) -> ByteString -> Bool
- maximum :: ByteString -> Word8
- minimum :: ByteString -> Word8
- 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
- mapAccumL :: (acc -> Word8 -> (acc, Word8)) -> acc -> ByteString -> (acc, ByteString)
- mapAccumR :: (acc -> Word8 -> (acc, Word8)) -> acc -> ByteString -> (acc, ByteString)
- replicate :: Int -> Word8 -> ByteString
- unfoldr :: (a -> Maybe (Word8, a)) -> a -> ByteString
- unfoldrN :: Int -> (a -> Maybe (Word8, a)) -> a -> (ByteString, Maybe a)
- take :: Int -> ByteString -> ByteString
- drop :: Int -> ByteString -> ByteString
- splitAt :: Int -> ByteString -> (ByteString, ByteString)
- takeWhile :: (Word8 -> Bool) -> ByteString -> ByteString
- dropWhile :: (Word8 -> Bool) -> ByteString -> ByteString
- span :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString)
- spanEnd :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString)
- break :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString)
- breakEnd :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString)
- group :: ByteString -> [ByteString]
- groupBy :: (Word8 -> Word8 -> Bool) -> ByteString -> [ByteString]
- inits :: ByteString -> [ByteString]
- tails :: ByteString -> [ByteString]
- split :: Word8 -> ByteString -> [ByteString]
- splitWith :: (Word8 -> Bool) -> ByteString -> [ByteString]
- isPrefixOf :: ByteString -> ByteString -> Bool
- isSuffixOf :: ByteString -> ByteString -> Bool
- isInfixOf :: ByteString -> ByteString -> Bool
- breakSubstring :: ByteString -> ByteString -> (ByteString, ByteString)
- findSubstring :: ByteString -> ByteString -> Maybe Int
- findSubstrings :: ByteString -> ByteString -> [Int]
- elem :: Word8 -> ByteString -> Bool
- notElem :: Word8 -> ByteString -> Bool
- find :: (Word8 -> Bool) -> ByteString -> Maybe Word8
- filter :: (Word8 -> Bool) -> ByteString -> ByteString
- partition :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString)
- index :: ByteString -> Int -> Word8
- elemIndex :: Word8 -> ByteString -> Maybe Int
- elemIndices :: Word8 -> ByteString -> [Int]
- elemIndexEnd :: Word8 -> ByteString -> Maybe Int
- findIndex :: (Word8 -> Bool) -> ByteString -> Maybe Int
- findIndices :: (Word8 -> Bool) -> ByteString -> [Int]
- count :: Word8 -> ByteString -> Int
- zip :: ByteString -> ByteString -> [(Word8, Word8)]
- zipWith :: (Word8 -> Word8 -> a) -> ByteString -> ByteString -> [a]
- unzip :: [(Word8, Word8)] -> (ByteString, ByteString)
- sort :: ByteString -> ByteString
- copy :: ByteString -> ByteString
- packCString :: CString -> IO ByteString
- packCStringLen :: CStringLen -> IO ByteString
- useAsCString :: ByteString -> (CString -> IO a) -> IO a
- useAsCStringLen :: ByteString -> (CStringLen -> IO a) -> IO a
- getLine :: IO ByteString
- getContents :: IO ByteString
- putStr :: ByteString -> IO ()
- putStrLn :: ByteString -> IO ()
- interact :: (ByteString -> ByteString) -> IO ()
- readFile :: FilePath -> IO ByteString
- writeFile :: FilePath -> ByteString -> IO ()
- appendFile :: FilePath -> ByteString -> IO ()
- hGetLine :: Handle -> IO ByteString
- hGetContents :: Handle -> IO ByteString
- hGet :: Handle -> Int -> IO ByteString
- hGetSome :: Handle -> Int -> IO ByteString
- hGetNonBlocking :: Handle -> Int -> IO ByteString
- hPut :: Handle -> ByteString -> IO ()
- hPutNonBlocking :: Handle -> ByteString -> IO ByteString
- hPutStr :: Handle -> ByteString -> IO ()
- hPutStrLn :: Handle -> ByteString -> IO ()
- breakByte :: Word8 -> ByteString -> (ByteString, ByteString)

# The `ByteString` type

data ByteString

A space-efficient representation of a `Word8` vector, supporting many efficient operations.

A `ByteString` contains 8-bit bytes, or by using the operations from Data.ByteString.Char8 it can be interpreted as containing 8-bit characters.

Instances

Eq ByteString |
Data ByteString |
Ord ByteString |
Read ByteString |
Show ByteString |
IsString ByteString |
Monoid ByteString |
NFData ByteString |
Typeable * ByteString |

# Introducing and eliminating `ByteString`s

empty :: ByteString

O(1) The empty `ByteString`

singleton :: Word8 -> ByteString

O(1) Convert a `Word8` into a `ByteString`

pack :: [Word8] -> ByteString

O(n) Convert a '[Word8]' into a `ByteString`.

For applications with large numbers of string literals, pack can be a bottleneck. In such cases, consider using packAddress (GHC only).

unpack :: ByteString -> [Word8]

O(n) Converts a `ByteString` to a '[Word8]'.

# Basic interface

cons :: Word8 -> ByteString -> ByteString infixr 5

O(n) `cons` is analogous to (:) for lists, but of different complexity, as it requires making a copy.

snoc :: ByteString -> Word8 -> ByteString infixl 5

O(n) Append a byte to the end of a `ByteString`

append :: ByteString -> ByteString -> ByteString

O(n) Append two ByteStrings

head :: ByteString -> Word8

O(1) Extract the first element of a ByteString, which must be non-empty. An exception will be thrown in the case of an empty ByteString.

uncons :: ByteString -> Maybe (Word8, ByteString)

O(1) Extract the head and tail of a ByteString, returning Nothing if it is empty.

unsnoc :: ByteString -> Maybe (ByteString, Word8)

O(1) Extract the `init` and `last` of a ByteString, returning Nothing if it is empty.

last :: ByteString -> Word8

O(1) Extract the last element of a ByteString, which must be finite and non-empty. An exception will be thrown in the case of an empty ByteString.

tail :: ByteString -> ByteString

O(1) Extract the elements after the head of a ByteString, which must be non-empty. An exception will be thrown in the case of an empty ByteString.

init :: ByteString -> ByteString

O(1) Return all the elements of a `ByteString` except the last one. An exception will be thrown in the case of an empty ByteString.

null :: ByteString -> Bool

O(1) Test whether a ByteString is empty.

length :: ByteString -> Int

O(1) `length` returns the length of a ByteString as an `Int`.

# Transforming ByteStrings

map :: (Word8 -> Word8) -> ByteString -> ByteString

O(n) `map` `f xs` is the ByteString obtained by applying `f` to each element of `xs`.

reverse :: ByteString -> ByteString

O(n) `reverse` `xs` efficiently returns the elements of `xs` in reverse order.

intersperse :: Word8 -> ByteString -> ByteString

O(n) 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.

intercalate :: ByteString -> [ByteString] -> ByteString

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.

transpose :: [ByteString] -> [ByteString]

The `transpose` function transposes the rows and columns of its `ByteString` argument.

# Reducing `ByteString`s (folds)

foldl :: (a -> Word8 -> a) -> a -> ByteString -> a

`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'` is like `foldl`, but strict in the accumulator.

foldl1 :: (Word8 -> Word8 -> Word8) -> ByteString -> Word8

`foldl1` is a variant of `foldl` that has no starting value argument, and thus must be applied to non-empty `ByteStrings`. An exception will be thrown in the case of an empty ByteString.

foldl1' :: (Word8 -> Word8 -> Word8) -> ByteString -> Word8

'foldl1\'' is like `foldl1`, but strict in the accumulator. An exception will be thrown in the case of an empty ByteString.

foldr :: (Word8 -> a -> a) -> a -> ByteString -> a

`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'` is like `foldr`, but strict in the accumulator.

foldr1 :: (Word8 -> Word8 -> Word8) -> ByteString -> Word8

`foldr1` is a variant of `foldr` that has no starting value argument, and thus must be applied to non-empty `ByteString`s An exception will be thrown in the case of an empty ByteString.

foldr1' :: (Word8 -> Word8 -> Word8) -> ByteString -> Word8

'foldr1\'' is a variant of `foldr1`, but is strict in the accumulator.

## Special folds

concat :: [ByteString] -> ByteString

O(n) Concatenate a list of ByteStrings.

concatMap :: (Word8 -> ByteString) -> ByteString -> ByteString

Map a function over a `ByteString` and concatenate the results

any :: (Word8 -> Bool) -> ByteString -> Bool

O(n) Applied to a predicate and a ByteString, `any` determines if any element of the `ByteString` satisfies the predicate.

all :: (Word8 -> Bool) -> ByteString -> Bool

O(n) Applied to a predicate and a `ByteString`, `all` determines if all elements of the `ByteString` satisfy the predicate.

maximum :: ByteString -> Word8

O(n) `maximum` returns the maximum value from a `ByteString` This function will fuse. An exception will be thrown in the case of an empty ByteString.

minimum :: ByteString -> Word8

O(n) `minimum` returns the minimum value from a `ByteString` This function will fuse. An exception will be thrown in the case of an empty ByteString.

# Building ByteStrings

## Scans

scanl :: (Word8 -> Word8 -> Word8) -> Word8 -> ByteString -> ByteString

`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.

scanl1 :: (Word8 -> Word8 -> Word8) -> ByteString -> ByteString

`scanl1` is a variant of `scanl` that has no starting value argument. This function will fuse.

    scanl1 f [x1, x2, ...] == [x1, x1 `f` x2, ...]

scanr :: (Word8 -> Word8 -> Word8) -> Word8 -> ByteString -> ByteString

scanr is the right-to-left dual of scanl.

scanr1 :: (Word8 -> Word8 -> Word8) -> ByteString -> ByteString

`scanr1` is a variant of `scanr` that has no starting value argument.

## Accumulating maps

mapAccumL :: (acc -> Word8 -> (acc, Word8)) -> acc -> ByteString -> (acc, ByteString)

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 list.

mapAccumR :: (acc -> Word8 -> (acc, Word8)) -> acc -> ByteString -> (acc, ByteString)

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.

## Generating and unfolding ByteStrings

replicate :: Int -> Word8 -> ByteString

O(n) `replicate` `n x` is a ByteString of length `n` with `x` the value of every element. The following holds:

    replicate w c = unfoldr w (\u -> Just (u,u)) c

This implemenation uses `memset(3)`

unfoldr :: (a -> Maybe (Word8, a)) -> a -> ByteString

O(n), where n is the length of the result. 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 the next byte in the string, and `b` is the seed value for further production.

Examples:

       unfoldr (\x -> if x <= 5 then Just (x, x + 1) else Nothing) 0
    == pack [0, 1, 2, 3, 4, 5]

unfoldrN :: Int -> (a -> Maybe (Word8, a)) -> a -> (ByteString, Maybe a)

O(n) Like `unfoldr`, `unfoldrN` builds a ByteString from a seed value. However, the length of the result is limited by the first argument to `unfoldrN`. This function is more efficient than `unfoldr` when the maximum length of the result is known.

The following equation relates `unfoldrN` and `unfoldr`:

    fst (unfoldrN n f s) == take n (unfoldr f s)

# Substrings

## Breaking strings

take :: Int -> ByteString -> ByteString

O(1) `take` `n`, applied to a ByteString `xs`, returns the prefix of `xs` of length `n`, or `xs` itself if `n > `length` xs`.

drop :: Int -> ByteString -> ByteString

O(1) `drop` `n xs` returns the suffix of `xs` after the first `n` elements, or `[]` if `n > `length` xs`.

splitAt :: Int -> ByteString -> (ByteString, ByteString)

O(1) `splitAt` `n xs` is equivalent to `(`take` n xs, `drop` n xs)`.

takeWhile :: (Word8 -> Bool) -> ByteString -> ByteString

`takeWhile`, applied to a predicate `p` and a ByteString `xs`, returns the longest prefix (possibly empty) of `xs` of elements that satisfy `p`.

dropWhile :: (Word8 -> Bool) -> ByteString -> ByteString

`dropWhile` `p xs` returns the suffix remaining after `takeWhile` `p xs`.

span :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString)

`span` `p xs` breaks the ByteString into two segments. It is equivalent to `(`takeWhile` p xs, `dropWhile` p xs)`

spanEnd :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString)

`spanEnd` behaves like `span` but from the end of the `ByteString`. We have

    spanEnd (not.isSpace) "x y z" == ("x y ","z")

and

    spanEnd (not . isSpace) ps
       ==
    let (x,y) = span (not.isSpace) (reverse ps) in (reverse y, reverse x)

break :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString)

`break` `p` is equivalent to ``span` (`not` . p)`.

Under GHC, a rewrite rule will transform break (==) into a call to the specialised breakByte:

    break ((==) x) = breakByte x
    break (==x) = breakByte x

breakEnd :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString)

`breakEnd` behaves like `break` but from the end of the `ByteString`

breakEnd p == spanEnd (not.p)

group :: ByteString -> [ByteString]

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. It is about 40% faster than groupBy (==)

groupBy :: (Word8 -> Word8 -> Bool) -> ByteString -> [ByteString]

The `groupBy` function is the non-overloaded version of `group`.

inits :: ByteString -> [ByteString]

O(n) Return all initial segments of the given `ByteString`, shortest first.

tails :: ByteString -> [ByteString]

O(n) Return all final segments of the given `ByteString`, longest first.

## Breaking into many substrings

split :: Word8 -> ByteString -> [ByteString]

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.

splitWith :: (Word8 -> Bool) -> ByteString -> [ByteString]

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') []        == []

# Predicates

isPrefixOf :: ByteString -> ByteString -> Bool

O(n) The `isPrefixOf` function takes two ByteStrings and returns `True` iff the first is a prefix of the second.

isSuffixOf :: ByteString -> ByteString -> Bool

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

However, the real implemenation uses memcmp to compare the end of the string only, with no reverse required..

isInfixOf :: ByteString -> ByteString -> Bool

Check whether one string is a substring of another. `isInfixOf p s` is equivalent to `not (null (findSubstrings p s))`.

## Search for arbitrary substrings

breakSubstring

Arguments

:: ByteString | String to search for
-> ByteString | String to search in
-> (ByteString, ByteString) | Head and tail of string broken at substring

Break a string on a substring, returning a pair of the part of the string prior to the match, and the rest of the string.

The following relationships hold:

    break (== c) l == breakSubstring (singleton c) l

and:

    findSubstring s l ==
       if null s then Just 0
                 else case breakSubstring s l of
                          (x,y) | null y    -> Nothing
                                | otherwise -> Just (length x)

For example, to tokenise a string, dropping delimiters:

    tokenise x y = h : if null t then [] else tokenise x (drop (length x) t)
        where (h,t) = breakSubstring x y

To skip to the first occurence of a string:

    snd (breakSubstring x y)

To take the parts of a string before a delimiter:

    fst (breakSubstring x y)

findSubstring

Arguments

:: ByteString | String to search for.
-> ByteString | String to seach in.
-> Maybe Int |

Deprecated: findSubstring is deprecated in favour of breakSubstring.

Get the first index of a substring in another string, or `Nothing` if the string is not found. `findSubstring p s` is equivalent to `listToMaybe (findSubstrings p s)`.

findSubstrings

Arguments

:: ByteString | String to search for.
-> ByteString | String to seach in.
-> [Int] |

Deprecated: findSubstrings is deprecated in favour of breakSubstring.

Find the indexes of all (possibly overlapping) occurances of a substring in a string.

# Searching ByteStrings

## Searching by equality

elem :: Word8 -> ByteString -> Bool

O(n) `elem` is the `ByteString` membership predicate.

notElem :: Word8 -> ByteString -> Bool

O(n) `notElem` is the inverse of `elem`

## Searching with a predicate

find :: (Word8 -> Bool) -> ByteString -> Maybe Word8

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

filter :: (Word8 -> Bool) -> ByteString -> ByteString

O(n) `filter`, applied to a predicate and a ByteString, returns a ByteString containing those characters that satisfy the predicate.

partition :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString)

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)

# Indexing ByteStrings

index :: ByteString -> Int -> Word8

O(1) `ByteString` index (subscript) operator, starting from 0.

elemIndex :: Word8 -> ByteString -> Maybe Int

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).

elemIndices :: Word8 -> ByteString -> [Int]

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).

elemIndexEnd :: Word8 -> ByteString -> Maybe Int

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)

findIndex :: (Word8 -> Bool) -> ByteString -> Maybe Int

The `findIndex` function takes a predicate and a `ByteString` and returns the index of the first element in the ByteString satisfying the predicate.

findIndices :: (Word8 -> Bool) -> ByteString -> [Int]

The `findIndices` function extends `findIndex`, by returning the indices of all elements satisfying the predicate, in ascending order.

count :: Word8 -> ByteString -> Int

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.

# Zipping and unzipping ByteStrings

zip :: ByteString -> ByteString -> [(Word8, Word8)]

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.

zipWith :: (Word8 -> Word8 -> a) -> ByteString -> ByteString -> [a]

`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.

unzip :: [(Word8, Word8)] -> (ByteString, ByteString)

O(n) `unzip` transforms a list of pairs of bytes into a pair of ByteStrings. Note that this performs two `pack` operations.

# Ordered ByteStrings

sort :: ByteString -> ByteString

O(n) Sort a ByteString efficiently, using counting sort.

# Low level conversions

## Copying ByteStrings

copy :: ByteString -> ByteString

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.

## Packing `CString`s and pointers

packCString :: CString -> IO ByteString

O(n). Construct a new `ByteString` from a `CString`. The resulting `ByteString` is an immutable copy of the original `CString`, and is managed on the Haskell heap. The original `CString` must be null terminated.

packCStringLen :: CStringLen -> IO ByteString

O(n). Construct a new `ByteString` from a `CStringLen`. The resulting `ByteString` is an immutable copy of the original `CStringLen`. The `ByteString` is a normal Haskell value and will be managed on the Haskell heap.

## Using ByteStrings as `CString`s

useAsCString :: ByteString -> (CString -> IO a) -> IO a

O(n) construction Use a `ByteString` with a function requiring a null-terminated `CString`. The `CString` is a copy and will be freed automatically.

useAsCStringLen :: ByteString -> (CStringLen -> IO a) -> IO a

O(n) construction Use a `ByteString` with a function requiring a `CStringLen`. As for `useAsCString` this function makes a copy of the original `ByteString`.

# I/O with `ByteString`s

## Standard input and output

getLine :: IO ByteString

Read a line from stdin.

getContents :: IO ByteString

getContents. Read stdin strictly. Equivalent to hGetContents stdin The `Handle` is closed after the contents have been read.

putStr :: ByteString -> IO ()

Write a ByteString to stdout

putStrLn :: ByteString -> IO ()

Deprecated: Use Data.ByteString.Char8.putStrLn instead. (Functions that rely on ASCII encodings belong in Data.ByteString.Char8)

Write a ByteString to stdout, appending a newline byte

interact :: (ByteString -> ByteString) -> IO ()

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.

## Files

readFile :: FilePath -> IO ByteString

Read an entire file strictly into a `ByteString`. This is far more efficient than reading the characters into a `String` and then using `pack`. It also may be more efficient than opening the file and reading it using `hGet`.

writeFile :: FilePath -> ByteString -> IO ()

Write a `ByteString` to a file.

appendFile :: FilePath -> ByteString -> IO ()

Append a `ByteString` to a file.

## I/O with Handles

hGetLine :: Handle -> IO ByteString

Read a line from a handle

hGetContents :: Handle -> IO ByteString

Read entire handle contents strictly into a `ByteString`.

This function reads chunks at a time, doubling the chunksize on each read. The final buffer is then realloced to the appropriate size. For files > half of available memory, this may lead to memory exhaustion. Consider using `readFile` in this case.

As with `hGet`, the string representation in the file is assumed to be ISO-8859-1.

The Handle is closed once the contents have been read, or if an exception is thrown.

hGet :: Handle -> Int -> IO ByteString

Read a `ByteString` directly from the specified `Handle`. This is far more efficient than reading the characters into a `String` and then using `pack`. First argument is the Handle to read from, and the second is the number of bytes to read. It returns the bytes read, up to n, or `null` if EOF has been reached.

`hGet` is implemented in terms of `hGetBuf`.

If the handle is a pipe or socket, and the writing end is closed, `hGet` will behave as if EOF was reached.

hGetSome :: Handle -> Int -> IO ByteString

Like `hGet`, except that a shorter `ByteString` may be returned if there are not enough bytes immediately available to satisfy the whole request. `hGetSome` only blocks if there is no data available, and EOF has not yet been reached.

hGetNonBlocking :: Handle -> Int -> IO ByteString

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`.

hPut :: Handle -> ByteString -> IO ()

Outputs a `ByteString` to the specified `Handle`.

hPutNonBlocking :: Handle -> ByteString -> IO ByteString

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`.

hPutStr :: Handle -> ByteString -> IO ()

A synonym for `hPut`, for compatibility

hPutStrLn :: Handle -> ByteString -> IO ()

Deprecated: Use Data.ByteString.Char8.hPutStrLn instead. (Functions that rely on ASCII encodings belong in Data.ByteString.Char8)

Write a ByteString to a handle, appending a newline byte

breakByte :: Word8 -> ByteString -> (ByteString, ByteString)

`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"