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Data.ByteString.Lazy.Char8

Contents

The `ByteString` type
Introducing and eliminating `ByteString`s
Basic interface
Transformating ByteStrings
Reducing `ByteString`s (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 `ByteString`s
  Standard input and output
  Files
  I/O with Handles

Description

Manipulate lazy `ByteString`s 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 `ByteString`s
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 `ByteString`s (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 `ByteString`s
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 `ByteString`s 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 `ByteString`s
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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