Data.ByteString.Lazy

bytestring-0.12.1.0: Fast, compact, strict and lazy byte strings with a list interface

Copyright | (c) Don Stewart 2006 (c) Duncan Coutts 2006-2011
License | BSD-style
Maintainer | dons00@gmail.com, duncan@community.haskell.org
Stability | stable
Portability | portable
Safe Haskell | Trustworthy
Language | Haskell2010

Data.ByteString.Lazy

Contents

- Lazy `ByteString`
- Introducing and eliminating `ByteString`s
- Basic interface
- Transforming ByteStrings
- Reducing `ByteString`s (folds)
  - Special folds
- Building ByteStrings
  - Scans
  - Accumulating maps
  - Infinite ByteStrings
  - 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
- I/O with `ByteString`s
  - Standard input and output
  - Files
  - I/O with Handles

Description

A time and space-efficient implementation of lazy byte vectors using lists of packed `Word8` arrays, suitable for high performance use, both in terms of large data quantities, or high speed requirements. Lazy ByteStrings are encoded as lazy lists of strict chunks of bytes.

A key feature of lazy ByteStrings is the means to manipulate large or unbounded streams of data without requiring the entire sequence to be resident in memory. To take advantage of this you have to write your functions in a lazy streaming style, e.g. classic pipeline composition. The default I/O chunk size is 32k, which should be good in most circumstances.

Some operations, such as `concat`, `append`, `reverse` and `cons`, have better complexity than their Data.ByteString equivalents, due to optimisations resulting from the list spine structure. For other operations lazy ByteStrings are usually within a few percent of strict ones.

The recomended way to assemble lazy ByteStrings from smaller parts is to use the builder monoid from Data.ByteString.Builder.

This module is intended to be imported `qualified`, to avoid name clashes with Prelude functions. eg.

    import qualified Data.ByteString.Lazy as B

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

Synopsis

- data ByteString
- type LazyByteString = ByteString
- empty :: ByteString
- singleton :: Word8 -> ByteString
- pack :: [Word8] -> ByteString
- unpack :: ByteString -> [Word8]
- fromStrict :: StrictByteString -> LazyByteString
- toStrict :: LazyByteString -> StrictByteString
- fromChunks :: [StrictByteString] -> LazyByteString
- toChunks :: LazyByteString -> [StrictByteString]
- foldrChunks :: (StrictByteString -> a -> a) -> a -> ByteString -> a
- foldlChunks :: (a -> StrictByteString -> a) -> a -> ByteString -> a
- cons :: Word8 -> ByteString -> ByteString
- cons' :: Word8 -> ByteString -> ByteString
- snoc :: ByteString -> Word8 -> ByteString
- append :: ByteString -> ByteString -> ByteString
- head :: HasCallStack => ByteString -> Word8
- uncons :: ByteString -> Maybe (Word8, ByteString)
- unsnoc :: ByteString -> Maybe (ByteString, Word8)
- last :: HasCallStack => ByteString -> Word8
- tail :: HasCallStack => ByteString -> ByteString
- init :: HasCallStack => ByteString -> ByteString
- null :: ByteString -> Bool
- length :: ByteString -> Int64
- 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 :: HasCallStack => (Word8 -> Word8 -> Word8) -> ByteString -> Word8
- foldl1' :: HasCallStack => (Word8 -> Word8 -> Word8) -> ByteString -> Word8
- foldr :: (Word8 -> a -> a) -> a -> ByteString -> a
- foldr' :: (Word8 -> a -> a) -> a -> ByteString -> a
- foldr1 :: HasCallStack => (Word8 -> Word8 -> Word8) -> ByteString -> Word8
- foldr1' :: HasCallStack => (Word8 -> Word8 -> Word8) -> ByteString -> Word8
- concat :: [ByteString] -> ByteString
- concatMap :: (Word8 -> ByteString) -> ByteString -> ByteString
- any :: (Word8 -> Bool) -> ByteString -> Bool
- all :: (Word8 -> Bool) -> ByteString -> Bool
- maximum :: HasCallStack => ByteString -> Word8
- minimum :: HasCallStack => ByteString -> Word8
- compareLength :: ByteString -> Int64 -> Ordering
- 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)
- repeat :: Word8 -> ByteString
- replicate :: Int64 -> Word8 -> ByteString
- cycle :: HasCallStack => ByteString -> ByteString
- iterate :: (Word8 -> Word8) -> Word8 -> ByteString
- unfoldr :: (a -> Maybe (Word8, a)) -> a -> ByteString
- take :: Int64 -> ByteString -> ByteString
- takeEnd :: Int64 -> ByteString -> ByteString
- drop :: Int64 -> ByteString -> ByteString
- dropEnd :: Int64 -> ByteString -> ByteString
- splitAt :: Int64 -> ByteString -> (ByteString, ByteString)
- takeWhile :: (Word8 -> Bool) -> ByteString -> ByteString
- takeWhileEnd :: (Word8 -> Bool) -> ByteString -> ByteString
- dropWhile :: (Word8 -> Bool) -> ByteString -> ByteString
- dropWhileEnd :: (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]
- initsNE :: ByteString -> NonEmpty ByteString
- tailsNE :: ByteString -> NonEmpty ByteString
- stripPrefix :: ByteString -> ByteString -> Maybe ByteString
- stripSuffix :: ByteString -> ByteString -> Maybe ByteString
- split :: Word8 -> ByteString -> [ByteString]
- splitWith :: (Word8 -> Bool) -> ByteString -> [ByteString]
- isPrefixOf :: ByteString -> ByteString -> Bool
- isSuffixOf :: ByteString -> ByteString -> Bool
- 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 :: HasCallStack => ByteString -> Int64 -> Word8
- indexMaybe :: ByteString -> Int64 -> Maybe Word8
- (!?) :: ByteString -> Int64 -> Maybe Word8
- elemIndex :: Word8 -> ByteString -> Maybe Int64
- elemIndexEnd :: Word8 -> ByteString -> Maybe Int64
- elemIndices :: Word8 -> ByteString -> [Int64]
- findIndex :: (Word8 -> Bool) -> ByteString -> Maybe Int64
- findIndexEnd :: (Word8 -> Bool) -> ByteString -> Maybe Int64
- findIndices :: (Word8 -> Bool) -> ByteString -> [Int64]
- count :: Word8 -> ByteString -> Int64
- zip :: ByteString -> ByteString -> [(Word8, Word8)]
- zipWith :: (Word8 -> Word8 -> a) -> ByteString -> ByteString -> [a]
- packZipWith :: (Word8 -> Word8 -> Word8) -> ByteString -> ByteString -> ByteString
- unzip :: [(Word8, Word8)] -> (ByteString, ByteString)
- copy :: ByteString -> ByteString
- getContents :: IO ByteString
- putStr :: ByteString -> IO ()
- interact :: (ByteString -> ByteString) -> IO ()
- readFile :: FilePath -> IO ByteString
- writeFile :: FilePath -> ByteString -> IO ()
- appendFile :: FilePath -> ByteString -> IO ()
- hGetContents :: Handle -> IO ByteString
- hGet :: Handle -> Int -> IO ByteString
- hGetNonBlocking :: Handle -> Int -> IO ByteString
- hPut :: Handle -> ByteString -> IO ()
- hPutNonBlocking :: Handle -> ByteString -> IO ByteString
- hPutStr :: Handle -> ByteString -> IO ()

# Lazy `ByteString`

data ByteString Source #

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

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

#### Instances

Instances details

NFData ByteString Source # |
Instance details Defined in Data.ByteString.Lazy.Internal Methods rnf :: ByteString -> () Source #
Monoid ByteString Source # |
Instance details Defined in Data.ByteString.Lazy.Internal Methods mempty :: ByteString # mappend :: ByteString -> ByteString -> ByteString # mconcat :: [ByteString] -> ByteString #
Semigroup ByteString Source # |
Instance details Defined in Data.ByteString.Lazy.Internal Methods (<>) :: ByteString -> ByteString -> ByteString # sconcat :: NonEmpty ByteString -> ByteString # stimes :: Integral b => b -> ByteString -> ByteString #
Data ByteString Source # |
Instance details Defined in Data.ByteString.Lazy.Internal 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 Source # | 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�
Instance details Defined in Data.ByteString.Lazy.Internal Methods fromString :: String -> ByteString #
IsList ByteString Source # | Since: bytestring-0.10.12.0
Instance details Defined in Data.ByteString.Lazy.Internal Associated Types
type Item ByteString |
Instance details Defined in Data.ByteString.Lazy.Internal type Item ByteString = Word8
Methods fromList :: [Item ByteString] -> ByteString # fromListN :: Int -> [Item ByteString] -> ByteString # toList :: ByteString -> [Item ByteString] #
Read ByteString Source # |
Instance details Defined in Data.ByteString.Lazy.Internal Methods readsPrec :: Int -> ReadS ByteString # readList :: ReadS [ByteString] # readPrec :: ReadPrec ByteString # readListPrec :: ReadPrec [ByteString] #
Show ByteString Source # |
Instance details Defined in Data.ByteString.Lazy.Internal Methods showsPrec :: Int -> ByteString -> ShowS # show :: ByteString -> String # showList :: [ByteString] -> ShowS #
Eq ByteString Source # |
Instance details Defined in Data.ByteString.Lazy.Internal Methods (==) :: ByteString -> ByteString -> Bool Source # (/=) :: ByteString -> ByteString -> Bool Source #
Ord ByteString Source # |
Instance details Defined in Data.ByteString.Lazy.Internal Methods compare :: ByteString -> ByteString -> Ordering Source # (<) :: ByteString -> ByteString -> Bool Source # (<=) :: ByteString -> ByteString -> Bool Source # (>) :: ByteString -> ByteString -> Bool Source # (>=) :: ByteString -> ByteString -> Bool Source # max :: ByteString -> ByteString -> ByteString Source # min :: ByteString -> ByteString -> ByteString Source #
Lift ByteString Source # |
Instance details Defined in Data.ByteString.Lazy.Internal Methods lift :: Quote m => ByteString -> m Exp Source # liftTyped :: forall (m :: Type -> Type). Quote m => ByteString -> Code m ByteString Source #
type Item ByteString Source # |
Instance details Defined in Data.ByteString.Lazy.Internal type Item ByteString = Word8

type LazyByteString = ByteString Source #

Type synonym for the lazy flavour of `ByteString`.

Since: bytestring-0.11.2.0

# Introducing and eliminating `ByteString`s

empty :: ByteString Source #

O(1) The empty `ByteString`

singleton :: Word8 -> ByteString Source #

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

pack :: [Word8] -> ByteString Source #

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

unpack :: ByteString -> [Word8] Source #

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

fromStrict :: StrictByteString -> LazyByteString Source #

O(1) Convert a `StrictByteString` into a `LazyByteString`.

toStrict :: LazyByteString -> StrictByteString Source #

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.

fromChunks :: [StrictByteString] -> LazyByteString Source #

O(c) Convert a list of `StrictByteString` into a `LazyByteString`

toChunks :: LazyByteString -> [StrictByteString] Source #

O(c) Convert a `LazyByteString` into a list of `StrictByteString`

foldrChunks :: (StrictByteString -> a -> a) -> a -> ByteString -> a Source #

Consume the chunks of a lazy ByteString with a natural right fold.

foldlChunks :: (a -> StrictByteString -> a) -> a -> ByteString -> a Source #

Consume the chunks of a lazy ByteString with a strict, tail-recursive, accumulating left fold.

# Basic interface

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

O(1) `cons` is analogous to `(:)` for lists.

cons' :: Word8 -> ByteString -> ByteString infixr 5 Source #

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.

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

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

append :: ByteString -> ByteString -> ByteString Source #

O(n/c) Append two ByteStrings

head :: HasCallStack => ByteString -> Word8 Source #

O(1) Extract the first element of a ByteString, which must be non-empty.

This is a partial function, consider using `uncons` instead.

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

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

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

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

- It is no faster than using `init` and `last`

last :: HasCallStack => ByteString -> Word8 Source #

O(n/c) Extract the last element of a ByteString, which must be finite and non-empty.

This is a partial function, consider using `unsnoc` instead.

tail :: HasCallStack => ByteString -> ByteString Source #

O(1) Extract the elements after the head of a ByteString, which must be non-empty.

This is a partial function, consider using `uncons` instead.

init :: HasCallStack => ByteString -> ByteString Source #

O(n/c) Returns all the elements of a `ByteString` except the last one.

This is a partial function, consider using `unsnoc` instead.

null :: ByteString -> Bool Source #

O(1) Test whether a ByteString is empty.

length :: ByteString -> Int64 Source #

O(c) `length` returns the length of a ByteString as an `Int64`

# Transforming ByteStrings

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

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

reverse :: ByteString -> ByteString Source #

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

intersperse :: Word8 -> ByteString -> ByteString Source #

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 Source #

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] Source #

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

# Reducing `ByteString`s (folds)

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

`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 Source #

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

foldl1 :: HasCallStack => (Word8 -> Word8 -> Word8) -> ByteString -> Word8 Source #

`foldl1` is a variant of `foldl` that has no starting value argument, and thus must be applied to non-empty `ByteString`s.

foldl1' :: HasCallStack => (Word8 -> Word8 -> Word8) -> ByteString -> Word8 Source #

`foldl1'` is like `foldl1`, but strict in the accumulator.

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

`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 Source #

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

Since: bytestring-0.11.2.0

foldr1 :: HasCallStack => (Word8 -> Word8 -> Word8) -> ByteString -> Word8 Source #

`foldr1` is a variant of `foldr` that has no starting value argument, and thus must be applied to non-empty `ByteString`s

foldr1' :: HasCallStack => (Word8 -> Word8 -> Word8) -> ByteString -> Word8 Source #

`foldr1'` is like `foldr1`, but strict in the accumulator.

Since: bytestring-0.11.2.0

## Special folds

concat :: [ByteString] -> ByteString Source #

O(n) Concatenate a list of ByteStrings.

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

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

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

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 Source #

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

maximum :: HasCallStack => ByteString -> Word8 Source #

O(n) `maximum` returns the maximum value from a `ByteString`

minimum :: HasCallStack => ByteString -> Word8 Source #

O(n) `minimum` returns the minimum value from a `ByteString`

compareLength :: ByteString -> Int64 -> Ordering Source #

O(c) `compareLength` compares the length of a `ByteString` to an `Int64`

Since: bytestring-0.11.1.0

# Building ByteStrings

## Scans

scanl Source #

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 Source #

`scanl1` is a variant of `scanl` that has no starting value argument.

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

Since: bytestring-0.11.2.0

scanr Source #

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

Since: bytestring-0.11.2.0

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

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

Since: bytestring-0.11.2.0

## Accumulating maps

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

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) Source #

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.

## Infinite ByteStrings

repeat :: Word8 -> ByteString Source #

``repeat` x` is an infinite ByteString, with `x` the value of every element.

replicate :: Int64 -> Word8 -> ByteString Source #

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

cycle :: HasCallStack => ByteString -> ByteString Source #

`cycle` ties a finite ByteString into a circular one, or equivalently, the infinite repetition of the original ByteString.

iterate :: (Word8 -> Word8) -> Word8 -> ByteString Source #

``iterate` f x` returns an infinite ByteString of repeated applications of `f` to `x`:

    iterate f x == [x, f x, f (f x), ...]

## Unfolding ByteStrings

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

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.

# Substrings

## Breaking strings

take :: Int64 -> ByteString -> ByteString Source #

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

takeEnd :: Int64 -> ByteString -> ByteString Source #

O(c) ``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: bytestring-0.11.2.0

drop :: Int64 -> ByteString -> ByteString Source #

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

dropEnd :: Int64 -> ByteString -> ByteString Source #

O(n) ``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: bytestring-0.11.2.0

splitAt :: Int64 -> ByteString -> (ByteString, ByteString) Source #

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

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

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

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

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

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

    >>> {-# LANGUAGE OverloadedLists #-)
    >>> takeWhileEnd even [1,2,3,4,6]
    [4,6]

Since: bytestring-0.11.2.0

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

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

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

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``.

    >>> {-# LANGUAGE OverloadedLists #-)
    >>> dropWhileEnd even [1,2,3,4,6]
    [1,2,3]

Since: bytestring-0.11.2.0

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

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) Source #

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 `(`takeWhileEnd` p &&& `dropWhileEnd` 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)

Since: bytestring-0.11.2.0

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

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))`.

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

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 `(`takeWhileEnd` (not . p) &&& `dropWhileEnd` (not . p))`.

Since: bytestring-0.11.2.0

group :: ByteString -> [ByteString] Source #

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.

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

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

inits :: ByteString -> [ByteString] Source #

Returns all initial segments of the given `ByteString`, shortest first.

tails :: ByteString -> [ByteString] Source #

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

initsNE :: ByteString -> NonEmpty ByteString Source #

Returns all initial segments of the given `ByteString`, shortest first.

Since: bytestring-0.11.4.0

tailsNE :: ByteString -> NonEmpty ByteString Source #

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

Since: bytestring-0.11.4.0

stripPrefix :: ByteString -> ByteString -> Maybe ByteString Source #

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: bytestring-0.10.8.0

stripSuffix :: ByteString -> ByteString -> Maybe ByteString Source #

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] Source #

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 `ByteString`s that are slices of the original.

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

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 Source #

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

isSuffixOf :: ByteString -> ByteString -> Bool Source #

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

## Search for arbitrary substrings

# Searching ByteStrings

## Searching by equality

elem :: Word8 -> ByteString -> Bool Source #

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

notElem :: Word8 -> ByteString -> Bool Source #

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

## Searching with a predicate

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

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 Source #

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) Source #

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 -> Int64 -> Word8 Source #

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

This is a partial function, consider using `indexMaybe` instead.

indexMaybe :: ByteString -> Int64 -> Maybe Word8 Source #

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

    0 <= n < length bs

Since: bytestring-0.11.0.0

(!?) :: ByteString -> Int64 -> Maybe Word8 Source #

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

    0 <= n < length bs

Since: bytestring-0.11.0.0

elemIndex :: Word8 -> ByteString -> Maybe Int64 Source #

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).

elemIndexEnd :: Word8 -> ByteString -> Maybe Int64 Source #

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)

Since: bytestring-0.10.6.0

elemIndices :: Word8 -> ByteString -> [Int64] Source #

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).

findIndex :: (Word8 -> Bool) -> ByteString -> Maybe Int64 Source #

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

findIndexEnd :: (Word8 -> Bool) -> ByteString -> Maybe Int64 Source #

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

Since: bytestring-0.10.12.0

findIndices :: (Word8 -> Bool) -> ByteString -> [Int64] Source #

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

count :: Word8 -> ByteString -> Int64 Source #

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)] Source #

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] Source #

`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 Source #

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

Since: bytestring-0.11.1.0

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

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

# Ordered ByteStrings

# Low level conversions

## Copying ByteStrings

copy :: ByteString -> ByteString Source #

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.

# I/O with `ByteString`s

⚠ Using lazy I/O functions like `readFile` or `hGetContents` means that the order of operations such as closing the file handle is left at the discretion of the RTS. Hence, the developer can face some issues when:

- The program reads a file and writes the same file. This means that the file may be locked because the handler has not been released when `writeFile` is executed.
- The program reads thousands of files, but due to lazy evaluation, the OS's file descriptor limit is reached before the handlers can be released.

### Why?

Consider the following program:

    import qualified Data.ByteString.Lazy as BL
    main = do
      _ <- BL.readFile "foo.txt"
      BL.writeFile "foo.txt" mempty

Generally, in the `IO` monad side effects happen sequentially and in full. Therefore, one might reasonably expect that reading the whole file via `readFile` executes all three actions (open the file handle, read its content, close the file handle) before control moves to the following `writeFile` action. This expectation holds for the strict Data.ByteString API. However, the above `LazyByteString` variant of the program fails with `openBinaryFile: resource busy (file is locked)`.

The reason for this is that Data.ByteString.Lazy is specifically designed to handle large or unbounded streams of data incrementally, without requiring all the data to be resident in memory at the same time. Incremental processing would not be possible if `readFile` were to follow the usual rules of `IO`: evaluating all side effects would require reading the file in full and closing its handle before returning from `readFile`. This is why `readFile` (and `hGetContents` in general) is implemented via `unsafeInterleaveIO`, which allows `IO` side effects to be delayed and interleaved with subsequent processing of the return value. That's exactly what happens in the example above: `readFile` opens a file handle, but since the content is not fully consumed, the file handle remains open, allowing the content to read on demand (never in this case, since the return value is ignored). So when `writeFile` is executed next, `foo.txt` is still open for reading and the RTS takes care to avoid simultaneously opening it for writing, instead returning the error shown above.

### How to enforce the order of effects?

If the content is small enough to fit in memory, consider using strict `readFile`, potentially applying `fromStrict` afterwards. E. g.,

    import qualified Data.ByteString as BS
    import qualified Data.ByteString.Lazy as BL
    main = do
      _ <- BS.readFile "foo.txt"
      BL.writeFile "foo.txt" mempty

If you are dealing with large or unbounded data streams, consider reaching out for a specialised package, such as conduit, machines-bytestring, pipes-bytestring, streaming-bytestring, streamly-bytestring, etc.

## Standard input and output

getContents :: IO ByteString Source #

getContents. Equivalent to hGetContents stdin. Will read lazily

putStr :: ByteString -> IO () Source #

Write a ByteString to `stdout`.

The chunks will be written one at a time. Other threads might write to the `stdout` in between, and hence `putStr` alone is not suitable for concurrent writes.

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

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 Source #

Read an entire file lazily into a `ByteString`.

The `Handle` will be held open until EOF is encountered.

Note that this function's implementation relies on `hGetContents`. The reader is advised to read its documentation.

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

Write a `ByteString` to a file.

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

Append a `ByteString` to a file.

## I/O with Handles

hGetContents :: Handle -> IO ByteString Source #

Read entire handle contents lazily into a `ByteString`. Chunks are read on demand, using the default chunk size.

File handles are closed on EOF if all the file is read, or through garbage collection otherwise.

hGet :: Handle -> Int -> IO ByteString Source #

Read `n` bytes into a `ByteString`, directly from the specified `Handle`.

hGetNonBlocking :: Handle -> Int -> IO ByteString Source #

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 () Source #

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

The chunks will be written one at a time. Other threads might write to the `Handle` in between, and hence `hPut` alone is not suitable for concurrent writes.

hPutNonBlocking :: Handle -> ByteString -> IO ByteString Source #

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 () Source #

A synonym for `hPut`, for compatibility