ByteString

A space-efficient representation of a Word8 vector, supporting many efficient operations.

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

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

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

Convert a bitvector into a lower-case ASCII hexadecimal string. This is helpful for visualizing raw binary data, rather than for parsing as such.

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

breakAfter pattern target splits target behind the first occurrence of pattern. An empty second component means that either the pattern does not occur in the target or the first occurrence of pattern is at the very end of target. To discriminate between those cases, use e.g. isSuffixOf.

  uncurry append . breakAfter pattern = id

breakEnd behaves like break but from the end of the ByteString

breakEnd p == spanEnd (not.p)

breakOn pattern target splits target at the first occurrence of pattern. If the pattern does not occur in the target, the second component of the result is empty, otherwise it starts with pattern. If the pattern is empty, the first component is empty.

  uncurry append . breakOn pattern = id

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)

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

O(n) Concatenate a list of ByteStrings.

Map a function over a ByteString and concatenate the results

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.

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(1) drop n xs returns the suffix of xs after the first n elements, or [] if n > length xs.

dropWhile p xs returns the suffix remaining after takeWhile p xs.

O(n) elem is the ByteString membership predicate.

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).

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)

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).

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

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

The findIndex function takes a predicate and a ByteString and returns the index of the first element in the ByteString satisfying the predicate.

The findIndices function extends findIndex, by returning the indices of all elements satisfying the predicate, in ascending order.

foldl' is like foldl, but strict in the accumulator.

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.

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 (==)

The groupBy function is the non-overloaded version of group.

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

indices finds the starting indices of all possibly overlapping occurrences of the pattern in the target string. If the pattern is empty, the result is [0 .. length target].

In general, not . null $ indices pat target is a much more efficient version of isInfixOf.

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

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.

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.

Check whether one string is a substring of another. isInfixOf p s is equivalent to not (null (findSubstrings p s)).

O(n) The isPrefixOf function takes two ByteStrings and returns True if the first is a prefix of the second.

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..

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

O(n) map f xs is the ByteString obtained by applying f to each element of xs.

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.

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.

nonOverlappingIndices finds the starting indices of all non-overlapping occurrences of the pattern in the target string. It is more efficient than removing indices from the list produced by indices.

O(n) notElem is the inverse of elem

O(1) Test whether a ByteString is empty.

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).

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.

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.

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)

Generate a random bytestring of length n. The PRNG is seeded from the system randomness source.

ioProperty $ ((fromIntegral n ===) . B.length) <$> random n

n > 4 ==> ioProperty $ (/=) <$> random n <*> random n

replace pat sub text replaces all (non-overlapping) occurrences of pat in text with sub. If occurrences of pat overlap, the first occurrence that does not overlap with a replaced previous occurrence is substituted. Occurrences of pat arising from a substitution will not be substituted. For example:

  replace "ana" "olog" "banana" = "bologna"
  replace "ana" "o" "bananana" = "bono"
  replace "aab" "abaa" "aaabb" = "aabaab"

The result is a lazy ByteString, which is lazily produced, without copying. Equality of pattern and substitution is not checked, but

  (concat . toChunks $ replace pat pat text) == text

holds. If the pattern is empty but not the substitution, the result is equivalent to (were they Strings) cycle sub.

For non-empty pat and sub a strict ByteString,

  fromChunks . intersperse sub . split pat = replace pat sub

and analogous relations hold for other types of sub.

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)

O(n) reverse xs efficiently returns the elements of xs in reverse order.

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.

scanl1 is a variant of scanl that has no starting value argument. This function will fuse.

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

scanr is the right-to-left dual of scanl.

scanr1 is a variant of scanr that has no starting value argument.

O(1) Convert a Word8 into a ByteString

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

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

span p xs breaks the ByteString into two segments. It is equivalent to (takeWhile p xs, dropWhile p xs)

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)

split pattern target splits target at each (non-overlapping) occurrence of pattern, removing pattern. If pattern is empty, the result is an infinite list of empty ByteStrings, if target is empty but not pattern, the result is an empty list, otherwise the following relations hold:

  concat . intersperse pat . split pat = id,
  length (split pattern target) ==
              length (nonOverlappingIndices pattern target) + 1,

no fragment in the result contains an occurrence of pattern.

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

splitKeepEnd pattern target splits target after each (non-overlapping) occurrence of pattern. If pattern is empty, the result is an infinite list of empty ByteStrings, otherwise the following relations hold:

  concat . splitKeepEnd pattern = id,

all fragments in the result except possibly the last end with pattern, no fragment contains more than one occurrence of pattern.

splitKeepFront is like splitKeepEnd, except that target is split before each occurrence of pattern and hence all fragments with the possible exception of the first begin with pattern. No fragment contains more than one non-overlapping occurrence of pattern.

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') []        == []

O(n) The stripPrefix function takes two ByteStrings and returns Just the remainder of the second iff the first is its prefix, and otherwise Nothing.

Since: bytestring-0.10.8.0

O(n) The stripSuffix function takes two ByteStrings and returns Just the remainder of the second iff the first is its suffix, and otherwise Nothing.

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

O(1) take n, applied to a ByteString xs, returns the prefix of xs of length n, or xs itself if n > length xs.

takeWhile, applied to a predicate p and a ByteString xs, returns the longest prefix (possibly empty) of xs of elements that satisfy p.

The transpose function transposes the rows and columns of its ByteString argument.

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

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]

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:

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

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

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

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

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

O(n) construction Use a ByteString with a function requiring a CStringLen. As for useAsCString this function makes a copy of the original ByteString. It must not be stored or used after the subcomputation finishes.

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.

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.

Traverse each Word8 in a strict or lazy ByteString

This Traversal walks each strict ByteString chunk in a tree-like fashion enable zippers to seek to locations more quickly and accelerate many monoidal queries, but up to associativity (and constant factors) it is equivalent to the much slower:

bytes ≡ unpackedBytes . traversed

anyOf bytes (== 0x80) :: ByteString -> Bool

pack (or unpack) a list of bytes into a strict or lazy ByteString.

pack x ≡ x ^. packedBytes
unpack x ≡ x ^. from packedBytes
packedBytes ≡ from unpackedBytes

unpack (or pack) a ByteString into a list of bytes

unpackedBytes ≡ from packedBytes
unpack x ≡ x ^. unpackedBytes
pack x ≡  x ^. from unpackedBytes

unpackedBytes :: Iso' ByteString [Word8]
unpackedBytes :: Iso' ByteString [Word8]