Data.ByteString.Char8

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 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 of groupBy, which allows the programmer to supply their own equality test. It is about 40% faster than groupBy (==)

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.

Applied to a predicate and a ByteString, all determines if all elements of the ByteString satisfy the predicate.

Applied to a predicate and a ByteString, any determines if any element of the ByteString satisfies the predicate.

O(n) Concatenate a list of ByteStrings.

Map a function over a ByteString and concatenate the results

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.

O(n) notElem is the inverse of elem

dropWhileEnd p xs returns the prefix remaining after takeWhileEnd p xs.

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.

O(n) The elemIndices function extends elemIndex, by returning the indices of all elements equal to the query element, in ascending order.

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.

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

O(n) Returns 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 Char and a ByteString and `intersperses' that Char between the elements of the ByteString. It is analogous to the intersperse function on Lists.

Check whether one string is a substring of another.

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

lines breaks a ByteString up into a list of ByteStrings at newline Chars ('\n'). The resulting strings do not contain newlines.

Note that it does not regard CR ('\r') as a newline character.

O(1) Convert a Char into a ByteString

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

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.

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

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

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 character in the string, and b is the seed value for further production.

Examples:

unfoldr (\x -> if x <= '9' then Just (x, succ x) else Nothing) '0' == "0123456789"

unlines joins lines, appending a terminating newline after each.

Equivalent to concat . Data.List.concatMap (\x -> [x, singleton '\n']).

The unwords function is analogous to the unlines function, on words.

words breaks a ByteString up into a list of words, which were delimited by Chars representing white space.

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.

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.

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

0 <= n < length bs

break p is equivalent to span (not . p).

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

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

A strict version of foldl1

O(1) Extract the first element of a ByteString, which must be non-empty.

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

This is a partial function, consider using unsnoc instead.

O(1) Extract the last element of a packed string, which must be non-empty.

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 implementation 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:

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:

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.

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

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

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.

This is a partial function, consider using uncons instead.

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.

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

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

unzip transforms a list of pairs of Chars into a pair of ByteStrings. Note that this performs two pack 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.

Try to read a signed Int value from the ByteString, returning Just (val, str) on success, where val is the value read and str is the rest of the input string. If the sequence of digits decodes to a value larger than can be represented by an Int, the returned value will be Nothing.

readInt does not ignore leading whitespace, the value must start immediately at the beginning of the input string.

Examples

>>> readInt "-1729 sum of cubes"Just (-1729," sum of cubes")>>> readInt "+1: readInt also accepts a leading '+'"Just (1, ": readInt also accepts a leading '+'")>>> readInt "not a decimal number"Nothing>>> readInt "12345678901234567890 overflows maxBound"Nothing>>> readInt "-12345678901234567890 underflows minBound"Nothing

Append a ByteString to a file.

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

Read a line from stdin.

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.

Write a ByteString to stdout.

Write a ByteString to stdout, appending a newline byte.

Unlike putStr, this is not atomic: other threads might write to stdout between writing of the bytestring and the newline.

Read an entire file strictly into a ByteString.

Write a ByteString to a file.

O(1) The empty ByteString

O(n) elem is the ByteString membership predicate. This implementation uses memchr(3).

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 like foldl, but strict in the accumulator.

foldl1 is a variant of foldl that has no starting value argument, and thus must be applied to non-empty ByteStrings.

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.

foldr' is a strict variant of foldr

foldr1 is a variant of foldr that has no starting value argument, and thus must be applied to non-empty ByteStrings

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

maximum returns the maximum value from a ByteString

minimum returns the minimum value from a ByteString

O(1) Test whether a ByteString is empty.

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

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

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

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

Outputs a ByteString to the specified Handle.

O(n) Converts a ByteString to a String.

O(n) Append two ByteStrings

O(n) Convert a String into a ByteString

For applications with large numbers of string literals, pack can be a bottleneck.

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:

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

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

O(n) Append a Char to the end of a ByteString. Similar to cons, this function performs a memcpy.

count returns the number of times its argument appears in the ByteString

count = length . elemIndices

Also

count '\n' == length . lines

But more efficiently than using length on the intermediate list.

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.

O(1) dropEnd n xs is equivalent to take (length xs - n) xs. Drops n elements from end of bytestring.

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

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

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"          == ["",""]
split undefined ""      == []  -- and not [""]

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.

Remove leading and trailing white space from a ByteString.

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) Returns all final segments of the given ByteString, longest first.

O(1) takeEnd n xs is equivalent to drop (length xs - n) xs. Takes n elements from end of bytestring.

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

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

O(1) Convert a StrictByteString into a LazyByteString.

O(n) Convert a LazyByteString into a StrictByteString.

Note that this is an expensive operation that forces the whole LazyByteString into memory and then copies all the data. If possible, try to avoid converting back and forth between strict and lazy bytestrings.

A strict variant of foldr1

breakEnd behaves like break but from the end of the ByteString

breakEnd p == spanEnd (not.p)

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(1) ByteString index, starting from 0, that returns Just if:

0 <= n < length bs

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.

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)

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 undefined ""      == []  -- and not [""]

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.

Beware that this function is not required to add a terminating NUL byte at the end of the CStringLen it provides. If you need to construct a pointer to a null-terminated sequence, use useAsCString (and measure length independently if desired).

Read a handle's entire contents strictly into a ByteString.

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 using readFile in this case.

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

Read a line from a handle

A synonym for hPut, for compatibility

Write a ByteString to a handle, appending a newline byte.

Unlike hPutStr, this is not atomic: other threads might write to the handle between writing of the bytestring and the newline.

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

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

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 empty if EOF has been reached.

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.

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. If there is no data available to be read, hGetNonBlocking returns empty.

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

Like hGet, except that a shorter ByteString 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.

Similar to hPut except that it will never block. Instead it returns any tail that did not get written. This tail may be empty 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 to hPut.

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

dropSpace efficiently returns the ByteString argument with white space Chars removed from the front. It is more efficient than calling dropWhile for removing whitespace. I.e.

dropWhile isSpace == dropSpace

A variant of readInt specialised to Int16.

A variant of readInt specialised to Int32.

A variant of readInt specialised to Int64.

A variant of readInt specialised to Int8.

Try to read a Word value from the ByteString, returning Just (val, str) on success, where val is the value read and str is the rest of the input string. If the sequence of digits decodes to a value larger than can be represented by a Word, the returned value will be Nothing.

readWord does not ignore leading whitespace, the value must start with a decimal digit immediately at the beginning of the input string. Leading + signs are not accepted.

Examples

>>> readWord "1729 sum of cubes"Just (1729," sum of cubes")>>> readWord "+1729 has an explicit sign"Nothing>>> readWord "not a decimal number"Nothing>>> readWord "98765432109876543210 overflows maxBound"Nothing

A variant of readWord specialised to Word16.

A variant of readWord specialised to Word32.

A variant of readWord specialised to Word64.

A variant of readWord specialised to Word8.

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 Integer read, and the rest of the string.

readInteger does not ignore leading whitespace, the value must start immediately at the beginning of the input string.

Examples

>>> readInteger "-000111222333444555666777888999 all done"Just (-111222333444555666777888999," all done")>>> readInteger "+1: readInteger also accepts a leading '+'"Just (1, ": readInteger also accepts a leading '+'")>>> readInteger "not a decimal number"Nothing

readNatural reads a Natural number from the beginning of the ByteString. If there is no Natural number at the beginning of the string, it returns Nothing, otherwise it just returns the number read, and the rest of the string.

readNatural does not ignore leading whitespace, the value must start with a decimal digit immediately at the beginning of the input string. Leading + signs are not accepted.

Examples

>>> readNatural "000111222333444555666777888999 all done"Just (111222333444555666777888999," all done")>>> readNatural "+000111222333444555666777888999 explicit sign"Nothing>>> readNatural "not a decimal number"Nothing