import qualified Data.ByteString.Lazy as B

The ByteString type

data ByteString Source

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.

Introducing and eliminating ByteStrings

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 :: ByteString -> ByteString Source

O(1) Convert a strict ByteString into a lazy ByteString.

toStrict :: ByteString -> ByteString Source

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 Source

O(c) Convert a list of strict ByteString into a lazy ByteString

toChunks :: ByteString -> [ByteString] Source

O(c) Convert a lazy ByteString into a list of strict ByteString

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

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

foldlChunks :: (a -> ByteString -> 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 :: ByteString -> Word8 Source

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

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 :: ByteString -> Word8 Source

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

tail :: ByteString -> ByteString Source

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

init :: ByteString -> ByteString Source

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

null :: ByteString -> Bool Source

O(1) Test whether a ByteString is empty.

length :: ByteString -> Int64 Source

O(n/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 ByteStrings 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 ByteStrings (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 :: (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 ByteStrings.

foldl1' :: (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.

foldr1 :: (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 ByteStrings

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 :: ByteString -> Word8 Source

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

minimum :: ByteString -> Word8 Source

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

Building ByteStrings

Scans

scanl :: (Word8 -> Word8 -> Word8) -> Word8 -> ByteString -> ByteString Source

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) 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 :: 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.

drop :: Int64 -> ByteString -> ByteString Source

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) Source

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

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

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 Source

dropWhile p xs returns the suffix remaining after takeWhile p xs.

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

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) Source

break p is equivalent to span (not . p).

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 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] Source

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

inits :: ByteString -> [ByteString] Source

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

tails :: ByteString -> [ByteString] Source

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

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 '\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] 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 (=='a') "aabbaca" == ["","","bb","c",""]
splitWith (=='a') []        == []

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 :: ByteString -> Int64 -> Word8 Source

O(c) ByteString index (subscript) operator, starting from 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 ==
(-) (length xs - 1) `fmap` elemIndex c (reverse xs)

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.

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.

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 ByteStrings

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

putStrLn :: ByteString -> IO () Source

Write a ByteString to stdout, appending a newline byte

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.

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.

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 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.

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