A space-efficient representation of aWord8 vector, supporting many efficient operations.

AByteString contains 8-bit bytes, or by using the operations fromData.ByteString.Char8 it can be interpreted as containing 8-bit characters.

Instances

Type synonym for the strict flavour ofByteString.

Since: 0.11.2.0

O(1) The emptyByteString

O(1) Convert aWord8 into aByteString

O(n) Convert a[Word8] into aByteString.

For applications with large numbers of string literals,pack can be a bottleneck. In such cases, consider usingunsafePackAddress (GHC only).

O(n) Converts aByteString to a[Word8].

O(1) Convert a strictByteString into a lazyByteString.

O(n) Convert a lazyByteString into a strictByteString.

Note that this is anexpensive 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.

Convert aFilePath to aByteString.

TheFilePath type is expected to use the file system encoding as reported bygetFileSystemEncoding. This encoding allows for round-tripping of arbitrary data on platforms that allow arbitrary bytes in their paths. This conversion function does the same thing thatopenFile would do when decoding theFilePath.

This function is inIO because the file system encoding can be changed. If the encoding can be assumed to be constant in your use case, you may invoke this function viaunsafePerformIO.

Since: 0.11.2.0

Convert aByteString to aFilePath.

This function uses the file system encoding, and resultingFilePaths can be safely used with standard IO functions and will reference the correct path in the presence of arbitrary non-UTF-8 encoded paths.

This function is inIO because the file system encoding can be changed. If the encoding can be assumed to be constant in your use case, you may invoke this function viaunsafePerformIO.

Since: 0.11.2.0

O(n)cons is analogous to (:) for lists, but of different complexity, as it requires making a copy.

O(n) Append a byte to the end of aByteString

O(n) Append two ByteStrings

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.

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

O(1) Extract theinit andlast of a ByteString, returning Nothing if it is empty.

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.

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.

O(1) Return all the elements of aByteString except the last one. An exception will be thrown in the case of an empty ByteString.

O(1) Test whether a ByteString is empty.

O(1)length returns the length of a ByteString as anInt.

O(n)mapf xs is the ByteString obtained by applyingf to each element ofxs.

O(n)reversexs efficiently returns the elements ofxs in reverse order.

O(n) Theintersperse function takes aWord8 and aByteString and `intersperses' that byte between the elements of theByteString. It is analogous to the intersperse function on Lists.

O(n) Theintercalate function takes aByteString and a list ofByteStrings and concatenates the list after interspersing the first argument between each element of the list.

Thetranspose function transposes the rows and columns of itsByteString argument.

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' is likefoldl, but strict in the accumulator.

foldl1 is a variant offoldl that has no starting value argument, and thus must be applied to non-emptyByteStrings. An exception will be thrown in the case of an empty ByteString.

foldl1' is likefoldl1, but strict in the accumulator. An exception will be thrown in the case of an empty ByteString.

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.

foldr' is likefoldr, but strict in the accumulator.

foldr1 is a variant offoldr that has no starting value argument, and thus must be applied to non-emptyByteStrings An exception will be thrown in the case of an empty ByteString.

foldr1' is a variant offoldr1, but is strict in the accumulator.

O(n) Concatenate a list of ByteStrings.

Map a function over aByteString and concatenate the results

O(n) Applied to a predicate and a ByteString,any determines if any element of theByteString satisfies the predicate.

O(n) Applied to a predicate and aByteString,all determines if all elements of theByteString satisfy the predicate.

O(n)maximum returns the maximum value from aByteString An exception will be thrown in the case of an empty ByteString.

O(n)minimum returns the minimum value from aByteString An exception will be thrown in the case of an empty ByteString.

Arguments

scanl is similar tofoldl, but returns a list of successive reduced values from the left.

scanl f z [x1, x2, ...] == [z, z `f` x1, (z `f` x1) `f` x2, ...]

Note that

head (scanl f z xs) == zlast (scanl f z xs) == foldl f z xs

scanl1 is a variant ofscanl that has no starting value argument.

scanl1 f [x1, x2, ...] == [x1, x1 `f` x2, ...]

Arguments

scanr is similar tofoldr, but returns a list of successive reduced values from the right.

scanr f z [..., x{n-1}, xn] == [..., x{n-1} `f` (xn `f` z), xn `f` z, z]

Note that

head (scanr f z xs) == foldr f z xslast (scanr f z xs) == z

scanr1 is a variant ofscanr that has no starting value argument.

ThemapAccumL function behaves like a combination ofmap andfoldl; 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.

ThemapAccumR function behaves like a combination ofmap andfoldr; 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.

O(n)replicaten x is a ByteString of lengthn withx the value of every element. The following holds:

replicate w c = unfoldr w (\u -> Just (u,u)) c

This implementation usesmemset(3)

O(n), wheren is the length of the result. Theunfoldr function is analogous to the List 'unfoldr'.unfoldr builds a ByteString from a seed value. The function takes the element and returnsNothing if it is done producing the ByteString or returnsJust(a,b), in which case,a is the next byte in the string, andb 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]

O(n) Likeunfoldr,unfoldrN builds a ByteString from a seed value. However, the length of the result is limited by the first argument tounfoldrN. This function is more efficient thanunfoldr when the maximum length of the result is known.

The following equation relatesunfoldrN andunfoldr:

fst (unfoldrN n f s) == take n (unfoldr f s)

O(1)taken, applied to a ByteStringxs, returns the prefix ofxs of lengthn, orxs itself ifn >length xs.

O(1)takeEnd n xs is equivalent todrop (length xs - n) xs. Takesn elements from end of bytestring.

>>>takeEnd 3 "abcdefg""efg">>>takeEnd 0 "abcdefg""">>>takeEnd 4 "abc""abc"

Since: 0.11.1.0

O(1)dropn xs returns the suffix ofxs after the firstn elements, orempty ifn >length xs.

O(1)dropEnd n xs is equivalent totake (length xs - n) xs. Dropsn elements from end of bytestring.

>>>dropEnd 3 "abcdefg""abcd">>>dropEnd 0 "abcdefg""abcdefg">>>dropEnd 4 "abc"""

Since: 0.11.1.0

O(1)splitAtn xs is equivalent to(take n xs,drop n xs).

Similar totakeWhile, returns the longest (possibly empty) prefix of elements satisfying the predicate.

Returns the longest (possibly empty) suffix of elements satisfying the predicate.

takeWhileEnd p is equivalent toreverse .takeWhile p .reverse.

Since: 0.10.12.0

Similar todropWhile, drops the longest (possibly empty) prefix of elements satisfying the predicate and returns the remainder.

Similar todropWhileEnd, drops the longest (possibly empty) suffix of elements satisfying the predicate and returns the remainder.

dropWhileEnd p is equivalent toreverse .dropWhile p .reverse.

Since: 0.10.12.0

Similar tospan, returns the longest (possibly empty) prefix of elements satisfying the predicate and the remainder of the string.

spanp is equivalent tobreak (not . p) and to(takeWhile p &&&dropWhile p).

Returns the longest (possibly empty) suffix of elements satisfying the predicate and the remainder of the string.

spanEndp is equivalent tobreakEnd (not . p) and to(takeWhileEnd p &&&dropWhileEnd p).

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)

Similar tobreak, returns the longest (possibly empty) prefix of elements whichdo not satisfy the predicate and the remainder of the string.

breakp is equivalent tospan (not . p) and to(takeWhile (not . p) &&&dropWhile (not . p)).

Under GHC, a rewrite rule will transform break (==) into a call to the specialised breakByte:

break ((==) x) = breakByte xbreak (==x) = breakByte x

Returns the longest (possibly empty) suffix of elements whichdo not satisfy the predicate and the remainder of the string.

breakEndp is equivalent tospanEnd (not . p) and to(takeWhileEnd (not . p) &&&dropWhileEnd (not . p)).

Thegroup function takes a ByteString and returns a list of ByteStrings such that the concatenation of the result is equal to the argument. Moreover, each string in the result contains only equal elements. For example,

group "Mississippi" = ["M","i","ss","i","ss","i","pp","i"]

It is a special case ofgroupBy, which allows the programmer to supply their own equality test. It is about 40% faster thangroupBy (==)

ThegroupBy function is the non-overloaded version ofgroup.

O(n) Return all initial segments of the givenByteString, shortest first.

O(n) Return all final segments of the givenByteString, longest first.

O(n) ThestripPrefix function takes two ByteStrings and returnsJust the remainder of the second iff the first is its prefix, and otherwiseNothing.

Since: 0.10.8.0

O(n) ThestripSuffix function takes two ByteStrings and returnsJust the remainder of the second iff the first is its suffix, and otherwiseNothing.

O(n) Break aByteString into pieces separated by the byte argument, consuming the delimiter. I.e.

split 10  "a\nb\nd\ne" == ["a","b","d","e"]   -- fromEnum '\n' == 10split 97  "aXaXaXa"    == ["","X","X","X",""] -- fromEnum 'a' == 97split 120 "x"          == ["",""]             -- fromEnum 'x' == 120split undefined ""     == []                  -- and not [""]

and

intercalate [c] . split c == idsplit == splitWith . (==)

As for all splitting functions in this library, this function does not copy the substrings, it just constructs newByteStrings that are slices of the original.

O(n) Splits aByteString 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 (==97) "aabbaca" == ["","","bb","c",""] -- fromEnum 'a' == 97splitWith undefined ""     == []                  -- and not [""]

O(n) TheisPrefixOf function takes two ByteStrings and returnsTrue if the first is a prefix of the second.

O(n) TheisSuffixOf function takes two ByteStrings and returnsTrue iff the first is a suffix of the second.

The following holds:

isSuffixOf x y == reverse x `isPrefixOf` reverse y

However, the real implementation uses memcmp to compare the end of the string only, with no reverse required..

Check whether one string is a substring of another.

O(n) Check whether aByteString represents valid UTF-8.

Since: 0.11.2.0

Arguments

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

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 occurrence of a string:

snd (breakSubstring x y)

To take the parts of a string before a delimiter:

fst (breakSubstring x y)

Note that calling `breakSubstring x` does some preprocessing work, so you should avoid unnecessarily duplicating breakSubstring calls with the same pattern.

O(n)elem is theByteString membership predicate.

O(n)notElem is the inverse ofelem

O(n) Thefind function takes a predicate and a ByteString, and returns the first element in matching the predicate, orNothing if there is no such element.

find f p = case findIndex f p of Just n -> Just (p ! n) ; _ -> Nothing

O(n)filter, applied to a predicate and a ByteString, returns a ByteString containing those characters that satisfy the predicate.

O(n) Thepartition 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)

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

O(1)ByteString index, starting from 0, that returnsJust if:

0 <= n < length bs

Since: 0.11.0.0

O(1)ByteString index, starting from 0, that returnsJust if:

0 <= n < length bs

Since: 0.11.0.0

O(n) TheelemIndex function returns the index of the first element in the givenByteString which is equal to the query element, orNothing if there is no such element. This implementation uses memchr(3).

O(n) TheelemIndices function extendselemIndex, by returning the indices of all elements equal to the query element, in ascending order. This implementation uses memchr(3).

O(n) TheelemIndexEnd function returns the last index of the element in the givenByteString which is equal to the query element, orNothing if there is no such element. The following holds:

elemIndexEnd c xs = case elemIndex c (reverse xs) of  Nothing -> Nothing  Just i  -> Just (length xs - 1 - i)

O(n) ThefindIndex function takes a predicate and aByteString and returns the index of the first element in the ByteString satisfying the predicate.

O(n) ThefindIndices function extendsfindIndex, by returning the indices of all elements satisfying the predicate, in ascending order.

O(n) ThefindIndexEnd function takes a predicate and aByteString and returns the index of the last element in the ByteString satisfying the predicate.

Since: 0.10.12.0

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.

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 ofunpack operations.

zipWith generaliseszip 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.

A specialised version ofzipWith for the common case of a simultaneous map over two ByteStrings, to build a 3rd.

Since: 0.11.1.0

O(n)unzip transforms a list of pairs of bytes into a pair of ByteStrings. Note that this performs twopack operations.

O(n) Sort a ByteString efficiently, using counting sort.

O(n) Make a copy of theByteString with its own storage. This is mainly useful to allow the rest of the data pointed to by theByteString 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.

O(n). Construct a newByteString from aCString. The resultingByteString is an immutable copy of the originalCString, and is managed on the Haskell heap. The originalCString must be null terminated.

O(n). Construct a newByteString from aCStringLen. The resultingByteString is an immutable copy of the originalCStringLen. TheByteString is a normal Haskell value and will be managed on the Haskell heap.

O(n) construction Use aByteString with a function requiring a null-terminatedCString. TheCString is a copy and will be freed automatically; it must not be stored or used after the subcomputation finishes.

O(n) construction Use aByteString with a function requiring aCStringLen. As foruseAsCString this function makes a copy of the originalByteString. It must not be stored or used after the subcomputation finishes.

Read a line from stdin.

getContents. Read stdin strictly. Equivalent to hGetContents stdin TheHandle is closed after the contents have been read.

Write a ByteString to stdout

The interact function takes a function of typeByteString -> 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.

Read an entire file strictly into aByteString.

Write aByteString to a file.

Append aByteString to a file.

Read a line from a handle

Read a handle's entire contents strictly into aByteString.

This function reads chunks at a time, increasing the chunk size on each read. The final string is then reallocated to the appropriate size. For files > half of available memory, this may lead to memory exhaustion. Consider usingreadFile in this case.

The Handle is closed once the contents have been read, or if an exception is thrown.

Read aByteString directly from the specifiedHandle. This is far more efficient than reading the characters into aString and then usingpack. 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, orempty if EOF has been reached.

hGet is implemented in terms ofhGetBuf.

If the handle is a pipe or socket, and the writing end is closed,hGet will behave as if EOF was reached.

LikehGet, except that a shorterByteString may be returned if there are not enough bytes immediately available to satisfy the whole request.hGetSome only blocks if there is no data available, and EOF has not yet been reached.

hGetNonBlocking is similar tohGet, 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 returnsempty.

Note: on Windows and with Haskell implementation other than GHC, this function does not work correctly; it behaves identically tohGet.

Outputs aByteString to the specifiedHandle.

Similar tohPut except that it will never block. Instead it returns any tail that did not get written. This tail may beempty 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 tohPut.

A synonym forhPut, for compatibility