bytestring-0.9.0.1: Fast, packed, strict and lazy byte arrays with a list interfaceContentsIndex
Data.ByteString.Lazy
Portabilityportable
Stabilityexperimental
Maintainerdons@cse.unsw.edu.au
Contents
The ByteString type
Introducing and eliminating ByteStrings
Basic interface
Transforming ByteStrings
Reducing ByteStrings (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 ByteStrings
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
data ByteString
empty :: ByteString
singleton :: Word8 -> ByteString
pack :: [Word8] -> ByteString
unpack :: ByteString -> [Word8]
fromChunks :: [ByteString] -> ByteString
toChunks :: ByteString -> [ByteString]
cons :: Word8 -> ByteString -> ByteString
cons' :: Word8 -> ByteString -> ByteString
snoc :: ByteString -> Word8 -> ByteString
append :: ByteString -> ByteString -> ByteString
head :: ByteString -> Word8
uncons :: ByteString -> Maybe (Word8, ByteString)
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)
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]
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
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]
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 ()
hPutStr :: Handle -> ByteString -> IO ()
The ByteString type
data ByteString

A space-efficient representation of a Word8 vector, supporting many efficient operations. A ByteString contains 8-bit characters only.

Instances of Eq, Ord, Read, Show, Data, Typeable

show/hide 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]'.
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.
cons' :: Word8 -> ByteString -> ByteString

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
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.
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
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
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 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

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.
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.
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 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
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) Return all initial segments of the given ByteString, shortest first.
tails :: ByteString -> [ByteString]
O(n) Return all final segments of the given ByteString, longest first.
Breaking into many substrings
split :: Word8 -> ByteString -> [ByteString]

O(n) Break a ByteString into pieces separated by the byte argument, consuming the delimiter. I.e.

 split '\n' "a\nb\nd\ne" == ["a","b","d","e"]
 split 'a'  "aXaXaXa"    == ["","X","X","X",""]
 split 'x'  "x"          == ["",""]

and

 intercalate [c] . split c == id
 split == splitWith . (==)

As for all splitting functions in this library, this function does not copy the substrings, it just constructs new ByteStrings that are slices of the original.

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

O(n) Splits a ByteString into components delimited by separators, where the predicate returns True for a separator element. The resulting components do not contain the separators. Two adjacent separators result in an empty component in the output. eg.

 splitWith (=='a') "aabbaca" == ["","","bb","c",""]
 splitWith (=='a') []        == []
Predicates
isPrefixOf :: ByteString -> ByteString -> Bool
O(n) The isPrefixOf function takes two ByteStrings and returns True iff the first is a prefix of the second.
isSuffixOf :: ByteString -> ByteString -> Bool

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

The following holds:

 isSuffixOf x y == reverse x `isPrefixOf` reverse y
Search for arbitrary substrings
Searching ByteStrings
Searching by equality
elem :: Word8 -> ByteString -> Bool
O(n) elem is the ByteString membership predicate.
notElem :: Word8 -> ByteString -> Bool
O(n) notElem is the inverse of elem
Searching with a predicate
find :: (Word8 -> Bool) -> ByteString -> Maybe Word8

O(n) The find function takes a predicate and a ByteString, and returns the first element in matching the predicate, or Nothing if there is no such element.

 find f p = case findIndex f p of Just n -> Just (p ! n) ; _ -> Nothing
filter :: (Word8 -> Bool) -> ByteString -> ByteString
O(n) filter, applied to a predicate and a ByteString, returns a ByteString containing those characters that satisfy the predicate.
partition :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString)

O(n) The partition function takes a predicate a ByteString and returns the pair of ByteStrings with elements which do and do not satisfy the predicate, respectively; i.e.,

 partition p bs == (filter p xs, filter (not . p) xs)
Indexing ByteStrings
index :: ByteString -> 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) zip takes two ByteStrings and returns a list of corresponding pairs of bytes. If one input ByteString is short, excess elements of the longer ByteString are discarded. This is equivalent to a pair of unpack operations.
zipWith :: (Word8 -> Word8 -> a) -> ByteString -> ByteString -> [a]
zipWith generalises zip by zipping with the function given as the first argument, instead of a tupling function. For example, zipWith (+) is applied to two ByteStrings to produce the list of corresponding sums.
unzip :: [(Word8, Word8)] -> (ByteString, ByteString)
O(n) unzip transforms a list of pairs of bytes into a pair of ByteStrings. Note that this performs two pack operations.
Ordered ByteStrings
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 ()
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.
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.
hPut :: Handle -> ByteString -> IO ()
Outputs a ByteString to the specified Handle.
hPutStr :: Handle -> ByteString -> IO ()
A synonym for hPut, for compatibility
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