| 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 | Haskell98 | 
Data.ByteString.Lazy
Contents
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
- empty :: ByteString
- singleton :: Word8 -> ByteString
- pack :: [Word8] -> ByteString
- unpack :: ByteString -> [Word8]
- fromStrict :: ByteString -> ByteString
- toStrict :: ByteString -> ByteString
- fromChunks :: [ByteString] -> ByteString
- toChunks :: ByteString -> [ByteString]
- foldrChunks :: (ByteString -> a -> a) -> a -> ByteString -> a
- foldlChunks :: (a -> ByteString -> a) -> a -> ByteString -> a
- cons :: Word8 -> ByteString -> ByteString
- cons' :: Word8 -> ByteString -> ByteString
- snoc :: ByteString -> Word8 -> ByteString
- append :: ByteString -> ByteString -> ByteString
- head :: ByteString -> Word8
- uncons :: ByteString -> Maybe (Word8, ByteString)
- unsnoc :: ByteString -> Maybe (ByteString, Word8)
- last :: ByteString -> Word8
- tail :: ByteString -> ByteString
- init :: ByteString -> ByteString
- null :: ByteString -> Bool
- length :: ByteString -> 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 :: (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)
- mapAccumR :: (acc -> Word8 -> (acc, Word8)) -> acc -> ByteString -> (acc, 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]
- 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 :: ByteString -> Int64 -> 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]
- unzip :: [(Word8, Word8)] -> (ByteString, ByteString)
- 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
- hGetNonBlocking :: Handle -> Int -> IO ByteString
- hPut :: Handle -> ByteString -> IO ()
- hPutNonBlocking :: Handle -> ByteString -> IO ByteString
- hPutStr :: Handle -> ByteString -> IO ()
The ByteString type
data ByteString #
A space-efficient representation of a Word8 vector, supporting many
 efficient operations.
A lazy ByteString contains 8-bit bytes, or by using the operations
 from Data.ByteString.Lazy.Char8 it can be interpreted as containing
 8-bit characters.
Instances
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.
unpack :: ByteString -> [Word8] #
O(n) Converts a ByteString to a '[Word8]'.
fromStrict :: ByteString -> ByteString #
O(1) Convert a strict ByteString into a lazy ByteString.
toStrict :: ByteString -> ByteString #
O(n) Convert a lazy ByteString into a strict ByteString.
Note that this is an expensive operation that forces the whole lazy ByteString into memory and then copies all the data. If possible, try to avoid converting back and forth between strict and lazy bytestrings.
fromChunks :: [ByteString] -> ByteString #
O(c) Convert a list of strict ByteString into a lazy ByteString
toChunks :: ByteString -> [ByteString] #
O(c) Convert a lazy ByteString into a list of strict ByteString
foldrChunks :: (ByteString -> a -> a) -> a -> ByteString -> a #
Consume the chunks of a lazy ByteString with a natural right fold.
foldlChunks :: (a -> ByteString -> a) -> a -> ByteString -> a #
Consume the chunks of a lazy ByteString with a strict, tail-recursive, accumulating left fold.
Basic interface
cons :: Word8 -> ByteString -> ByteString infixr 5 #
cons' :: Word8 -> ByteString -> ByteString infixr 5 #
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 #
O(n/c) Append a byte to the end of a ByteString
append :: ByteString -> ByteString -> ByteString #
O(n/c) Append two ByteStrings
head :: ByteString -> Word8 #
O(1) Extract the first element of a ByteString, which must be non-empty.
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) #
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.
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 returns the elements of xs in reverse order.
intersperse :: Word8 -> ByteString -> ByteString #
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 #
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.
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 ByteStrings
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 #
Accumulating maps
mapAccumL :: (acc -> Word8 -> (acc, Word8)) -> acc -> ByteString -> (acc, ByteString) #
mapAccumR :: (acc -> Word8 -> (acc, Word8)) -> acc -> ByteString -> (acc, ByteString) #
Infinite ByteStrings
repeat :: Word8 -> ByteString #
repeat xx the value of every
 element.
replicate :: Int64 -> Word8 -> ByteString #
O(n) replicate n xn 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 xf to x:
iterate f x == [x, f x, f (f x), ...]
Unfolding ByteStrings
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 #
drop :: Int64 -> ByteString -> ByteString #
splitAt :: Int64 -> ByteString -> (ByteString, ByteString) #
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 #
span :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString) #
break :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString) #
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] #
inits :: ByteString -> [ByteString] #
O(n) Return all initial segments of the given ByteString, shortest first.
tails :: ByteString -> [ByteString] #
O(n) Return all final segments of the given ByteString, longest first.
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: bytestring-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
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 (==97) [] == []
Predicates
isPrefixOf :: ByteString -> ByteString -> Bool #
O(n) The isPrefixOf function takes two ByteStrings and returns True
 iff the first is a prefix of the second.
isSuffixOf :: ByteString -> ByteString -> Bool #
O(n) The isSuffixOf function takes two ByteStrings and returns True
 iff the first is a suffix of the second.
The following holds:
isSuffixOf x y == reverse x `isPrefixOf` reverse y
Search for arbitrary substrings
Searching ByteStrings
Searching by equality
elem :: Word8 -> ByteString -> Bool #
O(n) elem is the ByteString membership predicate.
Searching with a predicate
filter :: (Word8 -> Bool) -> ByteString -> ByteString #
O(n) filter, applied to a predicate and a ByteString,
 returns a ByteString containing those characters that satisfy the
 predicate.
partition :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString) #
O(n) The partition function takes a predicate a ByteString and returns
 the pair of ByteStrings with elements which do and do not satisfy the
 predicate, respectively; i.e.,
partition p bs == (filter p xs, filter (not . p) xs)
Indexing ByteStrings
index :: ByteString -> 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).
elemIndexEnd :: Word8 -> ByteString -> Maybe Int64 #
O(n) The elemIndexEnd function returns the last index of the
 element in the given ByteString which is equal to the query
 element, or Nothing if there is no such element. The following
 holds:
elemIndexEnd c xs == (-) (length xs - 1) `fmap` elemIndex c (reverse xs)
Since: bytestring-0.10.6.0
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.
findIndexEnd :: (Word8 -> Bool) -> ByteString -> Maybe Int64 #
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] #
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)] #
zipWith :: (Word8 -> Word8 -> a) -> ByteString -> ByteString -> [a] #
unzip :: [(Word8, Word8)] -> (ByteString, ByteString) #
Ordered ByteStrings
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.
I/O with ByteStrings
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 () #
Deprecated: Use Data.ByteString.Lazy.Char8.putStrLn instead. (Functions that rely on ASCII encodings belong in Data.ByteString.Lazy.Char8)
Write a ByteString to stdout, appending a newline byte
interact :: (ByteString -> ByteString) -> IO () #
The interact function takes a function of type ByteString -> ByteString
 as its argument. The entire input from the standard input device is passed
 to this function as its argument, and the resulting string is output on the
 standard output device.
Files
readFile :: FilePath -> IO ByteString #
Read an entire file lazily into a ByteString.
 The Handle will be held open until EOF is encountered.
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.
Once EOF is encountered, the Handle is closed.
Note: the Handle should be placed in binary mode with
 hSetBinaryMode for hGetContents to
 work correctly.
hGet :: Handle -> Int -> IO ByteString #
Read n bytes into a ByteString, directly from 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.  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. The chunks will be
 written one at a time. Other threads might write to the Handle between the
 writes, and hence hPut alone might not be suitable for concurrent writes.
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