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Data.ByteString.Lazy

Contents

The `ByteString` type
Introducing and eliminating `ByteString`s
Basic interface
Transformating ByteStrings
Reducing `ByteString`s (folds)
  Special folds
Building ByteStrings
  Scans
  Accumulating maps
  Infinite ByteStrings
  Unfolding
Substrings
  Breaking strings
  Breaking into many substrings
  Joining strings
Predicates
Searching ByteStrings
  Searching by equality
  Searching with a predicate
Indexing ByteStrings
Zipping and unzipping ByteStrings
Ordered 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. Byte vectors are encoded as lazy lists of strict `Word8` arrays of bytes. They provide a means to manipulate large byte vectors without requiring the entire vector be resident in memory.

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. And for other operations Lazy ByteStrings are usually within a few percent of strict ones, but with better heap usage. For data larger than the available memory, or if you have tight memory constraints, this module will be the only option. The default chunk size is 64k, which should be good in most circumstances. For people with large L2 caches, you may want to increase this to fit your cache.

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. Polished and extended by Don Stewart. Lazy variant by Duncan Coutts and Don Stewart.

Synopsis

type ByteString = LazyByteString
empty :: ByteString
singleton :: Word8 -> ByteString
pack :: [Word8] -> ByteString
unpack :: ByteString -> [Word8]
fromChunks :: [ByteString] -> ByteString
toChunks :: ByteString -> [ByteString]
cons :: Word8 -> ByteString -> ByteString
snoc :: ByteString -> Word8 -> ByteString
append :: ByteString -> ByteString -> ByteString
head :: ByteString -> Word8
last :: ByteString -> Word8
tail :: ByteString -> ByteString
init :: ByteString -> ByteString
null :: ByteString -> Bool
length :: ByteString -> Int64
map :: (Word8 -> Word8) -> ByteString -> ByteString
reverse :: 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
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
mapAccumL :: (acc -> Word8 -> (acc, Word8)) -> acc -> ByteString -> (acc, ByteString)
mapIndexed :: (Int -> Word8 -> Word8) -> ByteString -> ByteString
repeat :: Word8 -> ByteString
replicate :: Int64 -> Word8 -> ByteString
cycle :: ByteString -> ByteString
iterate :: (Word8 -> Word8) -> Word8 -> ByteString
unfoldr :: (a -> Maybe (Word8, a)) -> a -> ByteString
take :: Int64 -> ByteString -> ByteString
drop :: Int64 -> ByteString -> ByteString
splitAt :: Int64 -> ByteString -> (ByteString, ByteString)
takeWhile :: (Word8 -> Bool) -> ByteString -> ByteString
dropWhile :: (Word8 -> Bool) -> ByteString -> ByteString
span :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString)
break :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString)
group :: ByteString -> [ByteString]
groupBy :: (Word8 -> Word8 -> Bool) -> ByteString -> [ByteString]
inits :: ByteString -> [ByteString]
tails :: ByteString -> [ByteString]
split :: Word8 -> ByteString -> [ByteString]
splitWith :: (Word8 -> Bool) -> ByteString -> [ByteString]
join :: ByteString -> [ByteString] -> ByteString
isPrefixOf :: ByteString -> ByteString -> Bool
elem :: Word8 -> ByteString -> Bool
notElem :: Word8 -> ByteString -> Bool
find :: (Word8 -> Bool) -> ByteString -> Maybe Word8
filter :: (Word8 -> Bool) -> ByteString -> ByteString
index :: ByteString -> Int64 -> Word8
elemIndex :: Word8 -> ByteString -> Maybe Int64
elemIndices :: Word8 -> ByteString -> [Int64]
findIndex :: (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]
copy :: ByteString -> 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 ()
hGetContents :: Handle -> IO ByteString
hGet :: Handle -> Int -> IO ByteString
hPut :: Handle -> ByteString -> IO ()
hGetNonBlocking :: Handle -> Int -> IO ByteString

The `ByteString` type
type ByteString = LazyByteString
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`.
unpack :: ByteString -> [Word8]
O(n) Converts a `ByteString` to a '[Word8]'.
fromChunks :: [ByteString] -> ByteString
O(c) Convert a list of strict `ByteString` into a lazy `ByteString`
toChunks :: ByteString -> [ByteString]
O(n) Convert a lazy `ByteString` into a list of strict `ByteString`
Basic interface
cons :: Word8 -> ByteString -> ByteString

O(1) `cons` is analogous to '(:)' for lists. Unlike '(:)' however it 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 `repeat` and `cycle` to build infinite lazy ByteStrings.

snoc :: ByteString -> Word8 -> ByteString
O(n/c) 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.
last :: ByteString -> Word8
O(n/c) Extract the last element of a ByteString, which must be finite and non-empty.
tail :: ByteString -> ByteString
O(1) Extract the elements after the head of a ByteString, which must be non-empty.
init :: ByteString -> ByteString
O(n/c) Return all the elements of a `ByteString` except the last one.
null :: ByteString -> Bool
O(1) Test whether a ByteString is empty.
length :: ByteString -> Int64
O(n/c) `length` returns the length of a ByteString as an `Int64`
Transformating 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.
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. This function is subject to array fusion.
foldl1' :: (Word8 -> Word8 -> Word8) -> ByteString -> Word8
`foldl1` is like `foldl1`, but strict in the accumulator.
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.
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
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`
minimum :: ByteString -> Word8
O(n) `minimum` returns the minimum value from a `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.

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.
mapIndexed :: (Int -> Word8 -> Word8) -> ByteString -> ByteString
O(n) map Word8 functions, provided with the index at each position
Infinite ByteStrings
repeat :: Word8 -> ByteString
``repeat` x` is an infinite ByteString, with `x` the value of every element.
replicate :: Int64 -> Word8 -> ByteString
O(n) ``replicate` n x` is a ByteString of length `n` with `x` the value of every element.
cycle :: ByteString -> ByteString
`cycle` ties a finite ByteString into a circular one, or equivalently, the infinite repetition of the original ByteString.
iterate :: (Word8 -> Word8) -> Word8 -> ByteString

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

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

Unfolding
unfoldr :: (a -> Maybe (Word8, a)) -> a -> ByteString
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
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`.
drop :: Int64 -> ByteString -> ByteString
O(n/c) `drop` `n xs` returns the suffix of `xs` after the first `n` elements, or `[]` if `n > `length` xs`.
splitAt :: Int64 -> ByteString -> (ByteString, ByteString)
O(n/c) `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)`
break :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString)
`break` `p` is equivalent to ``span` (`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.

groupBy :: (Word8 -> Word8 -> Bool) -> ByteString -> [ByteString]
The `groupBy` function is the non-overloaded version of `group`.
inits :: ByteString -> [ByteString]
O(n) unzip transforms a list of pairs of bytes into a pair of ByteStrings. Note that this performs two `pack` operations. 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

     join [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') []        == []

Joining strings
join :: ByteString -> [ByteString] -> ByteString
O(n) The `join` 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.
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.
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.
Indexing ByteStrings
index :: ByteString -> Int64 -> Word8
O(c) `ByteString` index (subscript) operator, starting from 0.
elemIndex :: Word8 -> ByteString -> Maybe Int64
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 -> [Int64]
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
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 -> [Int64]
The `findIndices` function extends `findIndex`, by returning the indices of all elements satisfying the predicate, in ascending order.
count :: Word8 -> ByteString -> Int64

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) 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..

isSuffixOf :: ByteString -> ByteString -> Bool isSuffixOf = error not yet implemented

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.
Ordered 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.
I/O with `ByteString`s
Standard input and output
getContents :: IO ByteString
getContents. Equivalent to hGetContents stdin. Will read lazily
putStr :: ByteString -> IO ()
Write a ByteString to stdout
putStrLn :: ByteString -> IO ()
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. It's great for writing one line programs!
Files
readFile :: FilePath -> IO ByteString
Read an entire file lazily 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
hGetContents :: Handle -> IO ByteString
Read entire handle contents lazily into a `ByteString`. Chunks are read on demand, using the default chunk size.
hGet :: Handle -> Int -> IO ByteString
Read `n` bytes into a `ByteString`, directly from the specified `Handle`.
hPut :: Handle -> ByteString -> IO ()
Outputs a `ByteString` to the specified `Handle`.
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.
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