Data.ByteString

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 and 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.

Strict ByteString

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

Data ByteString

Defined in Data.ByteString.Internal.Type

Methods

gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> ByteString -> c ByteString

gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c ByteString

toConstr :: ByteString -> Constr

dataTypeOf :: ByteString -> DataType

dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c ByteString)

dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c ByteString)

gmapT :: (forall b. Data b => b -> b) -> ByteString -> ByteString

gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> ByteString -> r

gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> ByteString -> r

gmapQ :: (forall d. Data d => d -> u) -> ByteString -> [u]

gmapQi :: Int -> (forall d. Data d => d -> u) -> ByteString -> u

gmapM :: Monad m => (forall d. Data d => d -> m d) -> ByteString -> m ByteString

gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> ByteString -> m ByteString

gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> ByteString -> m ByteString

IsString ByteString

Beware: fromString truncates multi-byte characters to octets. e.g. "枯朶に烏のとまりけり秋の暮" becomes �6k�nh~�Q��n�

Defined in Data.ByteString.Internal.Type

Methods

fromString :: String -> ByteString

Monoid ByteString

Defined in Data.ByteString.Internal.Type

Methods

mempty :: ByteString

mappend :: ByteString -> ByteString -> ByteString

mconcat :: [ByteString] -> ByteString

Semigroup ByteString

Defined in Data.ByteString.Internal.Type

Methods

(<>) :: ByteString -> ByteString -> ByteString

sconcat :: NonEmpty ByteString -> ByteString

stimes :: Integral b => b -> ByteString -> ByteString

IsList ByteString

Since: 0.10.12.0

Defined in Data.ByteString.Internal.Type

Associated Types

type Item ByteString

Methods

fromList :: [Item ByteString] -> ByteString

fromListN :: Int -> [Item ByteString] -> ByteString

toList :: ByteString -> [Item ByteString]

Read ByteString

Defined in Data.ByteString.Internal.Type

Methods

readsPrec :: Int -> ReadS ByteString

readList :: ReadS [ByteString]

readPrec :: ReadPrec ByteString

readListPrec :: ReadPrec [ByteString]

Show ByteString

Defined in Data.ByteString.Internal.Type

Methods

showsPrec :: Int -> ByteString -> ShowS

show :: ByteString -> String

showList :: [ByteString] -> ShowS

NFData ByteString

Defined in Data.ByteString.Internal.Type

Methods

rnf :: ByteString -> ()

Eq ByteString

Defined in Data.ByteString.Internal.Type

Methods

(==) :: ByteString -> ByteString -> Bool

(/=) :: ByteString -> ByteString -> Bool

Ord ByteString

Defined in Data.ByteString.Internal.Type

Methods

compare :: ByteString -> ByteString -> Ordering

(<) :: ByteString -> ByteString -> Bool

(<=) :: ByteString -> ByteString -> Bool

(>) :: ByteString -> ByteString -> Bool

(>=) :: ByteString -> ByteString -> Bool

max :: ByteString -> ByteString -> ByteString

min :: ByteString -> ByteString -> ByteString

Lift ByteString

Since: 0.11.2.0

Defined in Data.ByteString.Internal.Type

Methods

lift :: Quote m => ByteString -> m Exp

liftTyped :: forall (m :: Type -> Type). Quote m => ByteString -> Code m ByteString

type Item ByteString

Defined in Data.ByteString.Internal.Type

type Item ByteString = Word8

type StrictByteString = ByteString

Type synonym for the strict flavour of ByteString.

Since: 0.11.2.0

Heap fragmentation

With GHC, the ByteString representation uses pinned memory, meaning it cannot be moved by GC. While this is ideal for use with the foreign function interface and is usually efficient, this representation may lead to issues with heap fragmentation and wasted space if the program selectively retains a fraction of many small ByteStrings, keeping them live in memory over long durations.

While ByteString is indispensable when working with large blobs of data and especially when interfacing with native C libraries, be sure to also check the ShortByteString type. As a type backed by unpinned memory, ShortByteString behaves similarly to Text (from the text package) on the heap, completely avoids fragmentation issues, and in many use-cases may better suit your bytestring-storage needs.

Introducing and eliminating ByteStrings

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 unsafePackAddress (GHC only).

unpack :: ByteString -> [Word8]

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

fromStrict :: StrictByteString -> LazyByteString

O(1) Convert a StrictByteString into a LazyByteString.

toStrict :: LazyByteString -> StrictByteString

O(n) Convert a LazyByteString into a StrictByteString.

Note that this is an expensive operation that forces the whole LazyByteString into memory and then copies all the data. If possible, try to avoid converting back and forth between strict and lazy bytestrings.

fromFilePath :: FilePath -> IO ByteString

Convert a FilePath to a ByteString.

The FilePath type is expected to use the file system encoding as reported by getFileSystemEncoding. This encoding allows for round-tripping of arbitrary data on platforms that allow arbitrary bytes in their paths. This conversion function does the same thing that openFile would do when decoding the FilePath.

This function is in IO because the file system encoding can be changed. If the encoding can be assumed to be constant in your use case, you may invoke this function via unsafePerformIO.

Since: 0.11.2.0

toFilePath :: ByteString -> IO FilePath

Convert a ByteString to a FilePath.

This function uses the file system encoding, and resulting FilePaths can be safely used with standard IO functions and will reference the correct path in the presence of arbitrary non-UTF-8 encoded paths.

This function is in IO because the file system encoding can be changed. If the encoding can be assumed to be constant in your use case, you may invoke this function via unsafePerformIO.

Since: 0.11.2.0

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 :: HasCallStack => 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.

This is a partial function, consider using uncons instead.

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 :: HasCallStack => 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.

This is a partial function, consider using unsnoc instead.

tail :: HasCallStack => 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.

This is a partial function, consider using uncons instead.

init :: HasCallStack => ByteString -> ByteString

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

This is a partial function, consider using unsnoc instead.

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 ByteStrings 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 ByteStrings (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 :: HasCallStack => (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' :: HasCallStack => (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 :: HasCallStack => (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 ByteStrings An exception will be thrown in the case of an empty ByteString.

foldr1' :: HasCallStack => (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 :: HasCallStack => ByteString -> Word8

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

minimum :: HasCallStack => ByteString -> Word8

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

Building ByteStrings

Scans

scanl

Arguments

:: (Word8 -> Word8 -> Word8)

accumulator -> element -> new accumulator

-> Word8

starting value of accumulator

-> ByteString

input of length n

-> ByteString

output of length n+1

scanl is similar to foldl, but returns a list of successive reduced values from the left.

scanl f z [x1, x2, ...] == [z, z `f` x1, (z `f` x1) `f` x2, ...]

Note that

head (scanl f z xs) == z
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.

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

scanr

Arguments

:: (Word8 -> Word8 -> Word8)

element -> accumulator -> new accumulator

-> Word8

starting value of accumulator

-> ByteString

input of length n

-> ByteString

output of length n+1

scanr is similar to foldr, but returns a list of successive reduced values from the right.

scanr f z [..., x{n-1}, xn] == [..., x{n-1} `f` (xn `f` z), xn `f` z, z]

Note that

head (scanr f z xs) == foldr f z xs
last (scanr f z xs) == z

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 ByteString.

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 = fst (unfoldrN w (\u -> Just (u,u)) c)

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.

takeEnd :: Int -> ByteString -> ByteString

O(1) takeEnd n xs is equivalent to drop (length xs - n) xs. Takes n elements from end of bytestring.

>>> takeEnd 3 "abcdefg"
"efg"
>>> takeEnd 0 "abcdefg"
""
>>> takeEnd 4 "abc"
"abc"

Since: 0.11.1.0

drop :: Int -> ByteString -> ByteString

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

dropEnd :: Int -> ByteString -> ByteString

O(1) dropEnd n xs is equivalent to take (length xs - n) xs. Drops n elements from end of bytestring.

>>> dropEnd 3 "abcdefg"
"abcd"
>>> dropEnd 0 "abcdefg"
"abcdefg"
>>> dropEnd 4 "abc"
""

Since: 0.11.1.0

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

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

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

Similar to takeWhile, returns the longest (possibly empty) prefix of elements satisfying the predicate.

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

Returns the longest (possibly empty) suffix of elements satisfying the predicate.

takeWhileEnd p is equivalent to reverse . takeWhile p . reverse.

Since: 0.10.12.0

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

Similar to dropWhile, drops the longest (possibly empty) prefix of elements satisfying the predicate and returns the remainder.

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

Similar to dropWhileEnd, drops the longest (possibly empty) suffix of elements satisfying the predicate and returns the remainder.

dropWhileEnd p is equivalent to reverse . dropWhile p . reverse.

Since: 0.10.12.0

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

Similar to span, returns the longest (possibly empty) prefix of elements satisfying the predicate and the remainder of the string.

span p is equivalent to break (not . p) and to (takeWhile p &&& dropWhile p).

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

Returns the longest (possibly empty) suffix of elements satisfying the predicate and the remainder of the string.

spanEnd p is equivalent to breakEnd (not . p) and to (dropWhileEnd p &&& takeWhileEnd p).

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)

Similar to break, returns the longest (possibly empty) prefix of elements which do not satisfy the predicate and the remainder of the string.

break p is equivalent to span (not . p) and to (takeWhile (not . p) &&& dropWhile (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)

Returns the longest (possibly empty) suffix of elements which do not satisfy the predicate and the remainder of the string.

breakEnd p is equivalent to spanEnd (not . p) and to (dropWhileEnd (not . p) &&& takeWhileEnd (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 string 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) Returns all initial segments of the given ByteString, shortest first.

tails :: ByteString -> [ByteString]

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

initsNE :: ByteString -> NonEmpty ByteString

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

Since: 0.11.4.0

tailsNE :: ByteString -> NonEmpty ByteString

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

Since: 0.11.4.0

stripPrefix :: ByteString -> ByteString -> Maybe ByteString

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

stripSuffix :: ByteString -> ByteString -> Maybe ByteString

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.

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 10  "a\nb\nd\ne" == ["a","b","d","e"]   -- fromEnum '\n' == 10
split 97  "aXaXaXa"    == ["","X","X","X",""] -- fromEnum 'a' == 97
split 120 "x"          == ["",""]             -- fromEnum 'x' == 120
split undefined ""     == []                  -- and not [""]

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 (==97) "aabbaca" == ["","","bb","c",""] -- fromEnum 'a' == 97
splitWith undefined ""     == []                  -- and not [""]

Predicates

isPrefixOf :: ByteString -> ByteString -> Bool

O(n) The isPrefixOf function takes two ByteStrings and returns True if 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 implementation 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.

Encoding validation

isValidUtf8 :: ByteString -> Bool

O(n) Check whether a ByteString represents valid UTF-8.

Since: 0.11.2.0

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

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 occurrence of a string:

snd (breakSubstring x y)

To take the parts of a string before a delimiter:

fst (breakSubstring x y)

Note that calling `breakSubstring x` does some preprocessing work, so you should avoid unnecessarily duplicating breakSubstring calls with the same pattern.

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 :: HasCallStack => ByteString -> Int -> Word8

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

This is a partial function, consider using indexMaybe instead.

indexMaybe :: ByteString -> Int -> Maybe Word8

O(1) ByteString index, starting from 0, that returns Just if:

0 <= n < length bs

Since: 0.11.0.0

(!?) :: ByteString -> Int -> Maybe Word8

O(1) ByteString index, starting from 0, that returns Just if:

0 <= n < length bs

Since: 0.11.0.0

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 = case elemIndex c (reverse xs) of
  Nothing -> Nothing
  Just i  -> Just (length xs - 1 - i)

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

O(n) 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]

O(n) The findIndices function extends findIndex, by returning the indices of all elements satisfying the predicate, in ascending order.

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

O(n) The findIndexEnd function takes a predicate and a ByteString and returns the index of the last element in the ByteString satisfying the predicate.

Since: 0.10.12.0

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.

packZipWith :: (Word8 -> Word8 -> Word8) -> ByteString -> ByteString -> ByteString

A specialised version of zipWith for the common case of a simultaneous map over two ByteStrings, to build a 3rd.

Since: 0.11.1.0

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 CStrings 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 CStrings

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; it must not be stored or used after the subcomputation finishes.

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. It must not be stored or used after the subcomputation finishes.

Beware that this function is not required to add a terminating NUL byte at the end of the CStringLen it provides. If you need to construct a pointer to a null-terminated sequence, use useAsCString (and measure length independently if desired).

I/O with ByteStrings

Standard input and output

getLine :: IO ByteString

Deprecated: Deprecated since bytestring-0.12. Use getLine instead. (Functions that rely on ASCII encodings belong in Data.ByteString.Char8)

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.

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.

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

Deprecated: Deprecated since bytestring-0.12. Use hGetLine instead. (Functions that rely on ASCII encodings belong in Data.ByteString.Char8)

Read a line from a handle

hGetContents :: Handle -> IO ByteString

Read a handle's entire contents strictly into a ByteString.

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

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 empty 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