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Data.ByteString | Portability | portable | Stability | experimental | Maintainer | dons@cse.unsw.edu.au |
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Description |
A time and space-efficient implementation of byte vectors using
packed Word8 arrays, suitable for high performance use, both in terms
of large data quantities, or high speed requirements. Byte vectors
are encoded as strict Word8 arrays of bytes, held in a ForeignPtr,
and can be passed between C and Haskell with little effort.
This module is intended to be imported qualified, to avoid name
clashes with Prelude functions. eg.
import qualified Data.ByteString 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 ForeignPtr by David Roundy.
Polished and extended by Don Stewart.
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Synopsis |
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data ByteString | | empty :: ByteString | | singleton :: Word8 -> ByteString | | pack :: [Word8] -> ByteString | | unpack :: ByteString -> [Word8] | | 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 -> Int | | 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 | | foldr' :: (Word8 -> a -> a) -> a -> ByteString -> a | | foldr1 :: (Word8 -> Word8 -> Word8) -> ByteString -> Word8 | | 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 | | scanl1 :: (Word8 -> Word8 -> Word8) -> ByteString -> ByteString | | scanr :: (Word8 -> Word8 -> Word8) -> Word8 -> ByteString -> ByteString | | scanr1 :: (Word8 -> Word8 -> Word8) -> ByteString -> ByteString | | mapAccumL :: (acc -> Word8 -> (acc, Word8)) -> acc -> ByteString -> (acc, ByteString) | | mapAccumR :: (acc -> Word8 -> (acc, Word8)) -> acc -> ByteString -> (acc, ByteString) | | replicate :: Int -> Word8 -> ByteString | | unfoldr :: (a -> Maybe (Word8, a)) -> a -> ByteString | | unfoldrN :: Int -> (a -> Maybe (Word8, a)) -> a -> (ByteString, Maybe a) | | take :: Int -> ByteString -> ByteString | | drop :: Int -> ByteString -> ByteString | | splitAt :: Int -> ByteString -> (ByteString, ByteString) | | takeWhile :: (Word8 -> Bool) -> ByteString -> ByteString | | dropWhile :: (Word8 -> Bool) -> ByteString -> ByteString | | span :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString) | | spanEnd :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString) | | break :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString) | | breakEnd :: (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 | | isInfixOf :: ByteString -> ByteString -> Bool | | breakSubstring :: ByteString -> ByteString -> (ByteString, ByteString) | | findSubstring :: ByteString -> ByteString -> Maybe Int | | findSubstrings :: ByteString -> ByteString -> [Int] | | 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 -> Int -> Word8 | | elemIndex :: Word8 -> ByteString -> Maybe Int | | elemIndices :: Word8 -> ByteString -> [Int] | | elemIndexEnd :: Word8 -> ByteString -> Maybe Int | | findIndex :: (Word8 -> Bool) -> ByteString -> Maybe Int | | findIndices :: (Word8 -> Bool) -> ByteString -> [Int] | | count :: Word8 -> ByteString -> Int | | zip :: ByteString -> ByteString -> [(Word8, Word8)] | | zipWith :: (Word8 -> Word8 -> a) -> ByteString -> ByteString -> [a] | | unzip :: [(Word8, Word8)] -> (ByteString, ByteString) | | sort :: ByteString -> ByteString | | copy :: ByteString -> ByteString | | packCString :: CString -> IO ByteString | | packCStringLen :: CStringLen -> IO ByteString | | useAsCString :: ByteString -> (CString -> IO a) -> IO a | | useAsCStringLen :: ByteString -> (CStringLen -> IO a) -> IO a | | getLine :: IO 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 () | | hGetLine :: Handle -> IO ByteString | | hGetContents :: Handle -> IO ByteString | | hGet :: Handle -> Int -> IO ByteString | | hGetNonBlocking :: Handle -> Int -> IO ByteString | | hPut :: Handle -> ByteString -> IO () | | hPutStr :: Handle -> ByteString -> IO () | | hPutStrLn :: Handle -> ByteString -> IO () | | breakByte :: Word8 -> 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
| Instances | |
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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.
For applications with large numbers of string literals, pack can be a
bottleneck. In such cases, consider using packAddress (GHC only).
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O(n) Converts a ByteString to a '[Word8]'.
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Basic interface
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O(n) cons is analogous to (:) for lists, but of different
complexity, as it requires a memcpy.
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O(n) Append a byte to the end of a ByteString
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O(n) Append two ByteStrings
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O(1) Extract the first element of a ByteString, which must be non-empty.
An exception will be thrown in the case of an empty ByteString.
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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(1) Extract the last element of a ByteString, which must be finite and non-empty.
An exception will be thrown in the case of an empty ByteString.
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O(1) Extract the elements after the head of a ByteString, which must be non-empty.
An exception will be thrown in the case of an empty ByteString.
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O(1) Return all the elements of a ByteString except the last one.
An exception will be thrown in the case of an empty ByteString.
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O(1) Test whether a ByteString is empty.
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O(1) length returns the length of a ByteString as an Int.
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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. This function is subject to array fusion.
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O(n) reverse xs efficiently returns the elements of xs in reverse order.
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O(n) 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.
This function is subject to array fusion.
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'foldl\'' is like foldl, but strict in the accumulator.
However, for ByteStrings, all left folds are 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.
An exception will be thrown in the case of an empty ByteString.
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'foldl1\'' is like foldl1, but strict in the accumulator.
An exception will be thrown in the case of an empty ByteString.
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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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'foldr\'' is like foldr, but strict in the accumulator.
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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
An exception will be thrown in the case of an empty ByteString.
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'foldr1\'' is a variant of foldr1, but is strict in the
accumulator.
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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
This function will fuse.
An exception will be thrown in the case of an empty ByteString.
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O(n) minimum returns the minimum value from a ByteString
This function will fuse.
An exception will be thrown in the case of an empty 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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scanl1 is a variant of scanl that has no starting value argument.
This function will fuse.
scanl1 f [x1, x2, ...] == [x1, x1 `f` x2, ...]
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scanr is the right-to-left dual of scanl.
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scanr1 is a variant of scanr that has no starting value argument.
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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 list.
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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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Generating and unfolding ByteStrings
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O(n) replicate n x is a ByteString of length n with x
the value of every element. The following holds:
replicate w c = unfoldr w (\u -> Just (u,u)) c
This implemenation uses memset(3)
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O(n), where n is the length of the result. 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 the next byte in the string,
and b is the seed value for further production.
Examples:
unfoldr (\x -> if x <= 5 then Just (x, x + 1) else Nothing) 0
== pack [0, 1, 2, 3, 4, 5]
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O(n) Like unfoldr, unfoldrN builds a ByteString from a seed
value. However, the length of the result is limited by the first
argument to unfoldrN. This function is more efficient than unfoldr
when the maximum length of the result is known.
The following equation relates unfoldrN and unfoldr:
snd (unfoldrN n f s) == take n (unfoldr f s)
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Substrings
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Breaking strings
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O(1) 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(1) drop n xs returns the suffix of xs after the first n
elements, or [] if n > length xs.
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O(1) 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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spanEnd behaves like span but from the end of the ByteString.
We have
spanEnd (not.isSpace) "x y z" == ("x y ","z")
and
spanEnd (not . isSpace) ps
==
let (x,y) = span (not.isSpace) (reverse ps) in (reverse y, reverse x)
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break p is equivalent to span (not . p).
Under GHC, a rewrite rule will transform break (==) into a
call to the specialised breakByte:
break ((==) x) = breakByte x
break (==x) = breakByte x
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breakEnd behaves like break but from the end of the ByteString
breakEnd p == spanEnd (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. It is about 40% faster than
groupBy (==)
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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
However, the real implemenation uses memcmp to compare the end of the
string only, with no reverse required..
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Check whether one string is a substring of another. isInfixOf
p s is equivalent to not (null (findSubstrings p s)).
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Search for arbitrary substrings
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:: ByteString | String to search for
| -> ByteString | String to search in
| -> (ByteString, ByteString) | Head and tail of string broken at substring
| Break a string on a substring, returning a pair of the part of the
string prior to the match, and the rest of the string.
The following relationships hold:
break (== c) l == breakSubstring (singleton c) l
and:
findSubstring s l ==
if null s then Just 0
else case breakSubstring s l of
(x,y) | null y -> Nothing
| otherwise -> Just (length x)
For example, to tokenise a string, dropping delimiters:
tokenise x y = h : if null t then [] else tokenise x (drop (length x) t)
where (h,t) = breakSubstring x y
To skip to the first occurence of a string:
snd (breakSubstring x y)
To take the parts of a string before a delimiter:
fst (breakSubstring x y)
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:: ByteString | String to search for.
| -> ByteString | String to seach in.
| -> Maybe Int | | Get the first index of a substring in another string,
or Nothing if the string is not found.
findSubstring p s is equivalent to listToMaybe (findSubstrings p s).
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:: ByteString | String to search for.
| -> ByteString | String to seach in.
| -> [Int] | | Find the indexes of all (possibly overlapping) occurances of a
substring in a string.
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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. This function is subject to array fusion.
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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(1) 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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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)
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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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O(n) Sort a ByteString efficiently, using counting sort.
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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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Packing CStrings and pointers
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O(n). Construct a new ByteString from a CString. The
resulting ByteString is an immutable copy of the original
CString, and is managed on the Haskell heap. The original
CString must be null terminated.
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O(n). Construct a new ByteString from a CStringLen. The
resulting ByteString is an immutable copy of the original CStringLen.
The ByteString is a normal Haskell value and will be managed on the
Haskell heap.
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Using ByteStrings as CStrings
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O(n) construction Use a ByteString with a function requiring a
null-terminated CString. The CString will be freed
automatically. This is a memcpy(3).
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O(n) construction Use a ByteString with a function requiring a CStringLen.
As for useAsCString this function makes a copy of the original ByteString.
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I/O with ByteStrings
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Standard input and output
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Read a line from stdin.
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getContents. Read stdin strictly. Equivalent to hGetContents stdin
The Handle is closed after the contents have been read.
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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 strictly into a ByteString. This is far more
efficient than reading the characters into a String and then using
pack. It also may be more efficient than opening the file and
reading it using hGet. Files are read using 'binary mode' on Windows,
for 'text mode' use the Char8 version of this function.
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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 a line from a handle
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Read entire handle contents strictly into a ByteString.
This function reads chunks at a time, doubling the chunksize on each
read. The final buffer is then realloced to the appropriate size. For
files > half of available memory, this may lead to memory exhaustion.
Consider using readFile in this case.
As with hGet, the string representation in the file is assumed to
be ISO-8859-1.
The Handle is closed once the contents have been read,
or if an exception is thrown.
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Read a ByteString directly from the specified Handle. This
is far more efficient than reading the characters into a String
and then using pack. First argument is the Handle to read from,
and the second is the number of bytes to read. It returns the bytes
read, up to n, or null if EOF has been reached.
If there is any data to read, then hGet will not block, instead
it will return whatever data is available without blocking. It
only blocks if there is no data available to read.
hGet is implemented in terms of hGetBuf.
If the handle is a pipe or socket, and the writing end
is closed, hGet will behave as if EOF was reached.
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hGetNonBlocking is identical to hGet, except that it will never
block waiting for data to become available. If there is no data
available to be read, hGetNonBlocking returns null.
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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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Write a ByteString to a handle, appending a newline byte
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breakByte breaks its ByteString argument at the first occurence
of the specified byte. It is more efficient than break as it is
implemented with memchr(3). I.e.
break (=='c') "abcd" == breakByte 'c' "abcd"
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Produced by Haddock version 2.6.1 |