Data.ByteString.Lazy.Char8

Manipulate lazy ByteStrings using Char operations. All Chars will be truncated to 8 bits. It can be expected that these functions will run at identical speeds to their Word8 equivalents in Data.ByteString.Lazy.

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

 import qualified Data.ByteString.Lazy.Char8 as C

The Char8 interface to bytestrings provides an instance of IsString for the ByteString type, enabling you to use string literals, and have them implicitly packed to ByteStrings. Use {-# LANGUAGE OverloadedStrings #-} to enable this.

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

Eq ByteString

Data ByteString

Ord ByteString

Read ByteString

Show ByteString

Typeable ByteString

IsString ByteString

Monoid ByteString

NFData ByteString

Introducing and eliminating ByteStrings

empty :: ByteString

O(1) The empty ByteString

singleton :: Char -> ByteString

O(1) Convert a Char into a ByteString

pack :: [Char] -> ByteString

O(n) Convert a String into a ByteString.

unpack :: ByteString -> [Char]

O(n) Converts a ByteString to a String.

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

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.

Basic interface

cons :: Char -> ByteString -> ByteString

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

cons' :: Char -> 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 -> Char -> ByteString

O(n) Append a Char to the end of a ByteString. Similar to cons, this function performs a memcpy.

append :: ByteString -> ByteString -> ByteString

O(n\c)/ Append two ByteStrings

head :: ByteString -> Char

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

uncons :: ByteString -> Maybe (Char, ByteString)

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

last :: ByteString -> Char

O(1) Extract the last element of a packed string, which must be non-empty.

tail :: ByteString -> ByteString

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

unsnoc :: ByteString -> Maybe (ByteString, Char)

O(n\c)/ Extract the init and last of a ByteString, returning Nothing if it is 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 :: (Char -> Char) -> 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 :: Char -> ByteString -> ByteString

O(n) The intersperse function takes a Char and a ByteString and `intersperses' that Char 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 -> Char -> 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 -> Char -> a) -> a -> ByteString -> a

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

foldl1 :: (Char -> Char -> Char) -> ByteString -> Char

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

foldl1' :: (Char -> Char -> Char) -> ByteString -> Char

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

foldr :: (Char -> a -> a) -> a -> ByteString -> a

foldr, applied to a binary operator, a starting value (typically the right-identity of the operator), and a packed string, reduces the packed string using the binary operator, from right to left.

foldr1 :: (Char -> Char -> Char) -> ByteString -> Char

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 :: (Char -> ByteString) -> ByteString -> ByteString

Map a function over a ByteString and concatenate the results

any :: (Char -> Bool) -> ByteString -> Bool

Applied to a predicate and a ByteString, any determines if any element of the ByteString satisfies the predicate.

all :: (Char -> Bool) -> ByteString -> Bool

Applied to a predicate and a ByteString, all determines if all elements of the ByteString satisfy the predicate.

maximum :: ByteString -> Char

maximum returns the maximum value from a ByteString

minimum :: ByteString -> Char

minimum returns the minimum value from a ByteString

Building ByteStrings

Scans

scanl :: (Char -> Char -> Char) -> Char -> 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 -> Char -> (acc, Char)) -> 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 -> Char -> (acc, Char)) -> 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.

Infinite ByteStrings

repeat :: Char -> ByteString

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

replicate :: Int64 -> Char -> 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 :: (Char -> Char) -> Char -> 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 (Char, 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 :: (Char -> 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 :: (Char -> Bool) -> ByteString -> ByteString

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

span :: (Char -> Bool) -> ByteString -> (ByteString, ByteString)

span p xs breaks the ByteString into two segments. It is equivalent to (takeWhile p xs, dropWhile p xs)

break :: (Char -> 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 :: (Char -> Char -> 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 :: Char -> 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 :: (Char -> 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",""]

Breaking into lines and words

lines :: ByteString -> [ByteString]

lines breaks a ByteString up into a list of ByteStrings at newline Chars. The resulting strings do not contain newlines.

As of bytestring 0.9.0.3, this function is stricter than its list cousin.

words :: ByteString -> [ByteString]

words breaks a ByteString up into a list of words, which were delimited by Chars representing white space. And

 tokens isSpace = words

unlines :: [ByteString] -> ByteString

unlines is an inverse operation to lines. It joins lines, after appending a terminating newline to each.

unwords :: [ByteString] -> ByteString

The unwords function is analogous to the unlines function, on words.

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 :: Char -> ByteString -> Bool

O(n) elem is the ByteString membership predicate. This implementation uses memchr(3).

notElem :: Char -> ByteString -> Bool

O(n) notElem is the inverse of elem

Searching with a predicate

find :: (Char -> Bool) -> ByteString -> Maybe Char

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.

filter :: (Char -> 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 -> Char

O(1) ByteString index (subscript) operator, starting from 0.

elemIndex :: Char -> ByteString -> Maybe Int64

O(n) The elemIndex function returns the index of the first element in the given ByteString which is equal (by memchr) to the query element, or Nothing if there is no such element.

elemIndices :: Char -> ByteString -> [Int64]

O(n) The elemIndices function extends elemIndex, by returning the indices of all elements equal to the query element, in ascending order.

findIndex :: (Char -> 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 :: (Char -> Bool) -> ByteString -> [Int64]

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

count :: Char -> ByteString -> Int64

count returns the number of times its argument appears in the ByteString

 count      == length . elemIndices
 count '\n' == length . lines

But more efficiently than using length on the intermediate list.

Zipping and unzipping ByteStrings

zip :: ByteString -> ByteString -> [(Char, Char)]

O(n) zip takes two ByteStrings and returns a list of corresponding pairs of Chars. If one input ByteString is short, excess elements of the longer ByteString are discarded. This is equivalent to a pair of unpack operations, and so space usage may be large for multi-megabyte ByteStrings

zipWith :: (Char -> Char -> 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

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.

Reading from ByteStrings

readInt :: ByteString -> Maybe (Int, ByteString)

readInt reads an Int from the beginning of the ByteString. If there is no integer at the beginning of the string, it returns Nothing, otherwise it just returns the int read, and the rest of the string.

readInteger :: ByteString -> Maybe (Integer, ByteString)

readInteger reads an Integer from the beginning of the ByteString. If there is no integer at the beginning of the string, it returns Nothing, otherwise it just returns the int read, and the rest of the string.

I/O with ByteStrings

ByteString I/O uses binary mode, without any character decoding or newline conversion. The fact that it does not respect the Handle newline mode is considered a flaw and may be changed in a future version.

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.

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.

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.

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

hPutStrLn :: Handle -> ByteString -> IO ()

Write a ByteString to a handle, appending a newline byte