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Data.ByteString.Lazy | Portability | portable | Stability | experimental | Maintainer | dons@galois.com |
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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 Data.Array.Unboxed.UArray by Simon Marlow.
Rewritten to support slices and use Foreign.ForeignPtr.ForeignPtr
by David Roundy.
Polished and extended by Don Stewart.
Lazy variant by Duncan Coutts and Don Stewart.
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Synopsis |
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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 () | | join :: ByteString -> [ByteString] -> ByteString |
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The ByteString type
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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
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Introducing and eliminating ByteStrings
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O(1) The empty ByteString
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O(1) Convert a Word8 into a ByteString
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O(n) Convert a '[Word8]' into a ByteString.
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O(n) Converts a ByteString to a '[Word8]'.
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O(c) Convert a list of strict ByteString into a lazy ByteString
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O(n) Convert a lazy ByteString into a list of strict ByteString
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Basic interface
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O(1) cons is analogous to '(:)' for lists.
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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.
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O(n\c)/ Append a byte to the end of a ByteString
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O(n\c)/ Append two ByteStrings
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O(1) Extract the first element of a ByteString, which must be non-empty.
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O(1) Extract the head and tail of a ByteString, returning Nothing
if it is empty.
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O(n\c)/ Extract the last element of a ByteString, which must be finite
and non-empty.
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O(1) Extract the elements after the head of a ByteString, which must be
non-empty.
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O(n\c)/ Return all the elements of a ByteString except the last one.
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O(1) Test whether a ByteString is empty.
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O(n\c)/ length returns the length of a ByteString as an Int64
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Transforming ByteStrings
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O(n) map f xs is the ByteString obtained by applying f to each
element of xs.
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O(n) reverse xs returns the elements of xs in reverse order.
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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.
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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.
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The transpose function transposes the rows and columns of its
ByteString argument.
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Reducing ByteStrings (folds)
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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.
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'foldl\'' is like foldl, but strict in the accumulator.
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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.
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'foldl1\'' is like foldl1, but strict in the accumulator.
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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.
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foldr1 is a variant of foldr that has no starting value argument,
and thus must be applied to non-empty ByteStrings
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Special folds
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O(n) Concatenate a list of ByteStrings.
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Map a function over a ByteString and concatenate the results
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O(n) Applied to a predicate and a ByteString, any determines if
any element of the ByteString satisfies the predicate.
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O(n) Applied to a predicate and a ByteString, all determines
if all elements of the ByteString satisfy the predicate.
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O(n) maximum returns the maximum value from a ByteString
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O(n) minimum returns the minimum value from a ByteString
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Building ByteStrings
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Scans
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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.
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Accumulating maps
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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.
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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.
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O(n) map Word8 functions, provided with the index at each position
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Infinite ByteStrings
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repeat x is an infinite ByteString, with x the value of every
element.
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O(n) replicate n x is a ByteString of length n with x
the value of every element.
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cycle ties a finite ByteString into a circular one, or equivalently,
the infinite repetition of the original ByteString.
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iterate f x returns an infinite ByteString of repeated applications
of f to x:
iterate f x == [x, f x, f (f x), ...]
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Unfolding ByteStrings
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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.
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Substrings
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Breaking strings
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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.
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O(n\c)/ drop n xs returns the suffix of xs after the first n
elements, or [] if n > length xs.
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O(n\c)/ splitAt n xs is equivalent to (take n xs, drop n xs).
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takeWhile, applied to a predicate p and a ByteString xs,
returns the longest prefix (possibly empty) of xs of elements that
satisfy p.
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dropWhile p xs returns the suffix remaining after takeWhile p xs.
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span p xs breaks the ByteString into two segments. It is
equivalent to (takeWhile p xs, dropWhile p xs)
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break p is equivalent to span (not . p).
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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.
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The groupBy function is the non-overloaded version of group.
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O(n) Return all initial segments of the given ByteString, shortest first.
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O(n) Return all final segments of the given ByteString, longest first.
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Breaking into many substrings
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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.
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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') [] == []
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Predicates
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O(n) The isPrefixOf function takes two ByteStrings and returns True
iff the first is a prefix of the second.
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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
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Search for arbitrary substrings
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Searching ByteStrings
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Searching by equality
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O(n) elem is the ByteString membership predicate.
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O(n) notElem is the inverse of elem
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Searching with a predicate
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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
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O(n) filter, applied to a predicate and a ByteString,
returns a ByteString containing those characters that satisfy the
predicate.
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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)
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Indexing ByteStrings
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O(c) ByteString index (subscript) operator, starting from 0.
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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).
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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).
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The findIndex function takes a predicate and a ByteString and
returns the index of the first element in the ByteString
satisfying the predicate.
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The findIndices function extends findIndex, by returning the
indices of all elements satisfying the predicate, in ascending order.
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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.
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Zipping and unzipping ByteStrings
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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.
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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.
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O(n) unzip transforms a list of pairs of bytes into a pair of
ByteStrings. Note that this performs two pack operations.
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Ordered ByteStrings
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Low level conversions
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Copying ByteStrings
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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.
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I/O with ByteStrings
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Standard input and output
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getContents. Equivalent to hGetContents stdin. Will read lazily
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Write a ByteString to stdout
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Write a ByteString to stdout, appending a newline byte
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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.
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Files
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Read an entire file lazily into a ByteString.
The Handle will be held open until EOF is encountered.
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Write a ByteString to a file.
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Append a ByteString to a file.
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I/O with Handles
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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.
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Read n bytes into a ByteString, directly from the specified Handle.
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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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Outputs a ByteString to the specified Handle.
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A synonym for hPut, for compatibility
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Produced by Haddock version 2.1.0 |