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Data.ByteString.Lazy.Char8
Contents
The ByteString type
Introducing and eliminating ByteStrings
Basic interface
Transformating ByteStrings
Reducing ByteStrings (folds)
Special folds
Building ByteStrings
Scans
Accumulating maps
Infinite ByteStrings
Unfolding
Substrings
Breaking strings
Breaking into many substrings
Breaking into lines and words
Joining strings
Predicates
Searching ByteStrings
Searching by equality
Searching with a predicate
Indexing ByteStrings
Zipping and unzipping ByteStrings
Ordered ByteStrings
Reading from ByteStrings
I/O with ByteStrings
Standard input and output
Files
I/O with Handles
Description

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
Synopsis
type ByteString = LazyByteString
empty :: ByteString
singleton :: Char -> ByteString
pack :: [Char] -> ByteString
unpack :: ByteString -> [Char]
fromChunks :: [ByteString] -> ByteString
toChunks :: ByteString -> [ByteString]
cons :: Char -> ByteString -> ByteString
snoc :: ByteString -> Char -> ByteString
append :: ByteString -> ByteString -> ByteString
head :: ByteString -> Char
last :: ByteString -> Char
tail :: ByteString -> ByteString
init :: ByteString -> ByteString
null :: ByteString -> Bool
length :: ByteString -> Int64
map :: (Char -> Char) -> ByteString -> ByteString
reverse :: ByteString -> ByteString
transpose :: [ByteString] -> [ByteString]
foldl :: (a -> Char -> a) -> a -> ByteString -> a
foldl' :: (a -> Char -> a) -> a -> ByteString -> a
foldl1 :: (Char -> Char -> Char) -> ByteString -> Char
foldl1' :: (Char -> Char -> Char) -> ByteString -> Char
foldr :: (Char -> a -> a) -> a -> ByteString -> a
foldr1 :: (Char -> Char -> Char) -> ByteString -> Char
concat :: [ByteString] -> ByteString
concatMap :: (Char -> ByteString) -> ByteString -> ByteString
any :: (Char -> Bool) -> ByteString -> Bool
all :: (Char -> Bool) -> ByteString -> Bool
maximum :: ByteString -> Char
minimum :: ByteString -> Char
scanl :: (Char -> Char -> Char) -> Char -> ByteString -> ByteString
mapAccumL :: (acc -> Char -> (acc, Char)) -> acc -> ByteString -> (acc, ByteString)
mapIndexed :: (Int -> Char -> Char) -> ByteString -> ByteString
repeat :: Char -> ByteString
replicate :: Int64 -> Char -> ByteString
cycle :: [a] -> [a]
iterate :: (Char -> Char) -> Char -> ByteString
unfoldr :: (a -> Maybe (Char, a)) -> a -> ByteString
take :: Int64 -> ByteString -> ByteString
drop :: Int64 -> ByteString -> ByteString
splitAt :: Int64 -> ByteString -> (ByteString, ByteString)
takeWhile :: (Char -> Bool) -> ByteString -> ByteString
dropWhile :: (Char -> Bool) -> ByteString -> ByteString
span :: (Char -> Bool) -> ByteString -> (ByteString, ByteString)
break :: (Char -> Bool) -> ByteString -> (ByteString, ByteString)
group :: ByteString -> [ByteString]
groupBy :: (Char -> Char -> Bool) -> ByteString -> [ByteString]
inits :: ByteString -> [ByteString]
tails :: ByteString -> [ByteString]
split :: Char -> ByteString -> [ByteString]
splitWith :: (Char -> Bool) -> ByteString -> [ByteString]
lines :: ByteString -> [ByteString]
words :: ByteString -> [ByteString]
unlines :: [ByteString] -> ByteString
unwords :: [ByteString] -> ByteString
join :: ByteString -> [ByteString] -> ByteString
isPrefixOf :: ByteString -> ByteString -> Bool
elem :: Char -> ByteString -> Bool
notElem :: Char -> ByteString -> Bool
find :: (Char -> Bool) -> ByteString -> Maybe Char
filter :: (Char -> Bool) -> ByteString -> ByteString
index :: ByteString -> Int64 -> Char
elemIndex :: Char -> ByteString -> Maybe Int64
elemIndices :: Char -> ByteString -> [Int64]
findIndex :: (Char -> Bool) -> ByteString -> Maybe Int64
findIndices :: (Char -> Bool) -> ByteString -> [Int64]
count :: Char -> ByteString -> Int64
zip :: ByteString -> ByteString -> [(Char, Char)]
zipWith :: (Char -> Char -> a) -> ByteString -> ByteString -> [a]
copy :: ByteString -> ByteString
readInt :: ByteString -> Maybe (Int, ByteString)
readInteger :: ByteString -> Maybe (Integer, 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 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(n) Convert a lazy ByteString into a list of strict ByteString
Basic interface
cons :: Char -> ByteString -> ByteString
O(n) cons is analogous to (:) for lists, but of different complexity, as it requires a memcpy.
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) Append two ByteStrings
head :: ByteString -> Char
O(1) Extract the first element of a ByteString, which must be non-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.
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 :: (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 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 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.
mapIndexed :: (Int -> Char -> Char) -> ByteString -> ByteString
O(n) map Char functions, provided with the index at each position
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 :: [a] -> [a]
cycle ties a finite list into a circular one, or equivalently, the infinite repetition of the original list. It is the identity on infinite lists.
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
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) 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 :: 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

 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 :: (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.
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.
Joining strings
join :: ByteString -> [ByteString] -> ByteString
O(n) The join function takes a ByteString and a list of ByteStrings 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 :: 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
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
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. Use 'text mode' on Windows to interpret newlines
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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