bytestring-0.10.0.2: Fast, compact, strict and lazy byte strings with a list interface

Portability | portable
Stability | stable
Maintainer | dons00@gmail.com, duncan@community.haskell.org
Safe Haskell | Trustworthy

Data.ByteString.Char8

Contents

- The `ByteString` type
- Introducing and eliminating `ByteString`s
- Basic interface
- Transformating ByteStrings
- Reducing `ByteString`s (folds)
  - Special folds
- Building ByteStrings
  - Scans
  - Accumulating maps
  - Generating and unfolding ByteStrings
- Substrings
  - Breaking strings
  - Breaking into many substrings
  - Breaking into lines and words
- Predicates
  - Search for arbitrary substrings
- Searching ByteStrings
  - Searching by equality
  - Searching with a predicate
- Indexing ByteStrings
- Zipping and unzipping ByteStrings
- Ordered ByteStrings
- Reading from ByteStrings
- Low level CString conversions
  - Copying ByteStrings
  - Packing CStrings and pointers
  - Using ByteStrings as CStrings
- I/O with `ByteString`s
  - Standard input and output
  - Files
  - I/O with Handles

Description

Manipulate `ByteString`s using `Char` operations. All Chars will be truncated to 8 bits. It can be expected that these functions will run at identical speeds to their `Word8` equivalents in Data.ByteString.

More specifically these byte strings are taken to be in the subset of Unicode covered by code points 0-255. This covers Unicode Basic Latin, Latin-1 Supplement and C0+C1 Controls.

See:

- http://www.unicode.org/charts/
- http://www.unicode.org/charts/PDF/U0000.pdf
- http://www.unicode.org/charts/PDF/U0080.pdf

This module is intended to be imported `qualified`, to avoid name clashes with Prelude functions. eg.

     import qualified Data.ByteString.Char8 as C

The Char8 interface to bytestrings provides an instance of IsString for the ByteString type, enabling you to use string literals, and have them implicitly packed to ByteStrings. Use `{-# LANGUAGE OverloadedStrings #-}` to enable this.

Synopsis

- data ByteString
- empty :: ByteString
- singleton :: Char -> ByteString
- pack :: String -> ByteString
- unpack :: ByteString -> [Char]
- cons :: Char -> ByteString -> ByteString
- snoc :: ByteString -> Char -> ByteString
- append :: ByteString -> ByteString -> ByteString
- head :: ByteString -> Char
- uncons :: ByteString -> Maybe (Char, ByteString)
- last :: ByteString -> Char
- tail :: ByteString -> ByteString
- init :: ByteString -> ByteString
- null :: ByteString -> Bool
- length :: ByteString -> Int
- map :: (Char -> Char) -> ByteString -> ByteString
- reverse :: ByteString -> ByteString
- intersperse :: Char -> ByteString -> ByteString
- intercalate :: ByteString -> [ByteString] -> ByteString
- transpose :: [ByteString] -> [ByteString]
- foldl :: (a -> Char -> a) -> a -> ByteString -> a
- foldl' :: (a -> Char -> a) -> a -> ByteString -> a
- foldl1 :: (Char -> Char -> Char) -> ByteString -> Char
- foldl1' :: (Char -> Char -> Char) -> ByteString -> Char
- foldr :: (Char -> a -> a) -> a -> ByteString -> a
- foldr' :: (Char -> a -> a) -> a -> ByteString -> a
- foldr1 :: (Char -> Char -> Char) -> ByteString -> Char
- foldr1' :: (Char -> Char -> Char) -> ByteString -> Char
- concat :: [ByteString] -> ByteString
- concatMap :: (Char -> ByteString) -> ByteString -> ByteString
- any :: (Char -> Bool) -> ByteString -> Bool
- all :: (Char -> Bool) -> ByteString -> Bool
- maximum :: ByteString -> Char
- minimum :: ByteString -> Char
- scanl :: (Char -> Char -> Char) -> Char -> ByteString -> ByteString
- scanl1 :: (Char -> Char -> Char) -> ByteString -> ByteString
- scanr :: (Char -> Char -> Char) -> Char -> ByteString -> ByteString
- scanr1 :: (Char -> Char -> Char) -> ByteString -> ByteString
- mapAccumL :: (acc -> Char -> (acc, Char)) -> acc -> ByteString -> (acc, ByteString)
- mapAccumR :: (acc -> Char -> (acc, Char)) -> acc -> ByteString -> (acc, ByteString)
- replicate :: Int -> Char -> ByteString
- unfoldr :: (a -> Maybe (Char, a)) -> a -> ByteString
- unfoldrN :: Int -> (a -> Maybe (Char, a)) -> a -> (ByteString, Maybe a)
- take :: Int -> ByteString -> ByteString
- drop :: Int -> ByteString -> ByteString
- splitAt :: Int -> ByteString -> (ByteString, ByteString)
- takeWhile :: (Char -> Bool) -> ByteString -> ByteString
- dropWhile :: (Char -> Bool) -> ByteString -> ByteString
- span :: (Char -> Bool) -> ByteString -> (ByteString, ByteString)
- spanEnd :: (Char -> Bool) -> ByteString -> (ByteString, ByteString)
- break :: (Char -> Bool) -> ByteString -> (ByteString, ByteString)
- breakEnd :: (Char -> Bool) -> ByteString -> (ByteString, ByteString)
- group :: ByteString -> [ByteString]
- groupBy :: (Char -> Char -> Bool) -> ByteString -> [ByteString]
- inits :: ByteString -> [ByteString]
- tails :: ByteString -> [ByteString]
- split :: Char -> ByteString -> [ByteString]
- splitWith :: (Char -> Bool) -> ByteString -> [ByteString]
- lines :: ByteString -> [ByteString]
- words :: ByteString -> [ByteString]
- unlines :: [ByteString] -> ByteString
- unwords :: [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 :: Char -> ByteString -> Bool
- notElem :: Char -> ByteString -> Bool
- find :: (Char -> Bool) -> ByteString -> Maybe Char
- filter :: (Char -> Bool) -> ByteString -> ByteString
- index :: ByteString -> Int -> Char
- elemIndex :: Char -> ByteString -> Maybe Int
- elemIndices :: Char -> ByteString -> [Int]
- elemIndexEnd :: Char -> ByteString -> Maybe Int
- findIndex :: (Char -> Bool) -> ByteString -> Maybe Int
- findIndices :: (Char -> Bool) -> ByteString -> [Int]
- count :: Char -> ByteString -> Int
- zip :: ByteString -> ByteString -> [(Char, Char)]
- zipWith :: (Char -> Char -> a) -> ByteString -> ByteString -> [a]
- unzip :: [(Char, Char)] -> (ByteString, ByteString)
- sort :: ByteString -> ByteString
- readInt :: ByteString -> Maybe (Int, ByteString)
- readInteger :: ByteString -> Maybe (Integer, 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 ()
- hPutNonBlocking :: Handle -> ByteString -> IO ByteString
- hPutStr :: Handle -> ByteString -> IO ()
- hPutStrLn :: Handle -> ByteString -> IO ()

# The `ByteString` type

data ByteString

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

Eq ByteString |
Data ByteString |
Ord ByteString |
Read ByteString |
Show ByteString |
Typeable ByteString |
IsString ByteString |
Monoid ByteString |
NFData ByteString |

# Introducing and eliminating `ByteString`s

empty :: ByteString

O(1) The empty `ByteString`

singleton :: Char -> ByteString

O(1) Convert a `Char` into a `ByteString`

pack :: String -> ByteString

O(n) Convert a `String` into a `ByteString`

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

unpack :: ByteString -> [Char]

O(n) Converts a `ByteString` to a `String`.

# Basic interface

cons :: Char -> ByteString -> ByteString

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

snoc :: ByteString -> Char -> ByteString

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

append :: ByteString -> ByteString -> ByteString

O(n) Append two ByteStrings

head :: ByteString -> Char

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

uncons :: ByteString -> Maybe (Char, ByteString)

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

last :: ByteString -> Char

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

tail :: ByteString -> 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.

init :: ByteString -> ByteString

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.

null :: ByteString -> Bool

O(1) Test whether a ByteString is empty.

length :: ByteString -> Int

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

# Transformating ByteStrings

map :: (Char -> Char) -> ByteString -> ByteString

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

reverse :: ByteString -> ByteString

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

intersperse :: Char -> ByteString -> ByteString

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.

intercalate :: ByteString -> [ByteString] -> ByteString

O(n) The `intercalate` function takes a `ByteString` and a list of `ByteString`s and concatenates the list after interspersing the first argument between each element of the list.

transpose :: [ByteString] -> [ByteString]

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

# Reducing `ByteString`s (folds)

foldl :: (a -> Char -> a) -> a -> ByteString -> a

`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' :: (a -> Char -> a) -> a -> ByteString -> a

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

foldl1 :: (Char -> Char -> Char) -> ByteString -> Char

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

foldl1' :: (Char -> Char -> Char) -> ByteString -> Char

A strict version of `foldl1`

foldr :: (Char -> a -> a) -> a -> ByteString -> a

`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' :: (Char -> a -> a) -> a -> ByteString -> a

'foldr\'' is a strict variant of foldr

foldr1 :: (Char -> Char -> Char) -> ByteString -> Char

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

foldr1' :: (Char -> Char -> Char) -> ByteString -> Char

A strict variant of foldr1

## Special folds

concat :: [ByteString] -> ByteString

O(n) Concatenate a list of ByteStrings.

concatMap :: (Char -> ByteString) -> ByteString -> ByteString

Map a function over a `ByteString` and concatenate the results

any :: (Char -> Bool) -> ByteString -> Bool

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

all :: (Char -> Bool) -> ByteString -> Bool

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

maximum :: ByteString -> Char

`maximum` returns the maximum value from a `ByteString`

minimum :: ByteString -> Char

`minimum` returns the minimum value from a `ByteString`

# Building ByteStrings

## Scans

scanl :: (Char -> Char -> Char) -> Char -> ByteString -> ByteString

`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 :: (Char -> Char -> Char) -> ByteString -> ByteString

`scanl1` is a variant of `scanl` that has no starting value argument:

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

scanr :: (Char -> Char -> Char) -> Char -> ByteString -> ByteString

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

scanr1 :: (Char -> Char -> Char) -> ByteString -> ByteString

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

## Accumulating maps

mapAccumL :: (acc -> Char -> (acc, Char)) -> acc -> ByteString -> (acc, ByteString)

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.

mapAccumR :: (acc -> Char -> (acc, Char)) -> acc -> ByteString -> (acc, 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.

## Generating and unfolding ByteStrings

replicate :: Int -> Char -> ByteString

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)`

unfoldr :: (a -> Maybe (Char, a)) -> a -> ByteString

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"

unfoldrN :: Int -> (a -> Maybe (Char, a)) -> a -> (ByteString, Maybe a)

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)

# Substrings

## Breaking strings

take :: Int -> ByteString -> ByteString

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

drop :: Int -> ByteString -> ByteString

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

splitAt :: Int -> ByteString -> (ByteString, ByteString)

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

takeWhile :: (Char -> Bool) -> ByteString -> ByteString

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

dropWhile :: (Char -> Bool) -> ByteString -> ByteString

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

span :: (Char -> Bool) -> ByteString -> (ByteString, ByteString)

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

spanEnd :: (Char -> Bool) -> ByteString -> (ByteString, ByteString)

`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)

break :: (Char -> Bool) -> ByteString -> (ByteString, ByteString)

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

breakEnd :: (Char -> Bool) -> ByteString -> (ByteString, ByteString)

`breakEnd` behaves like `break` but from the end of the `ByteString`

breakEnd p == spanEnd (not.p)

group :: ByteString -> [ByteString]

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 (==)

groupBy :: (Char -> Char -> Bool) -> ByteString -> [ByteString]

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

inits :: ByteString -> [ByteString]

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

tails :: ByteString -> [ByteString]

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

## Breaking into many substrings

split :: Char -> ByteString -> [ByteString]

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.

splitWith :: (Char -> Bool) -> ByteString -> [ByteString]

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",""]

## Breaking into lines and words

lines :: ByteString -> [ByteString]

`lines` breaks a ByteString up into a list of ByteStrings at newline Chars. The resulting strings do not contain newlines.

words :: ByteString -> [ByteString]

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

unlines :: [ByteString] -> ByteString

`unlines` is an inverse operation to `lines`. It joins lines, after appending a terminating newline to each.

unwords :: [ByteString] -> ByteString

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

# Predicates

isPrefixOf :: ByteString -> ByteString -> Bool

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

isSuffixOf :: ByteString -> ByteString -> Bool

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..

isInfixOf :: ByteString -> ByteString -> Bool

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

## Search for arbitrary substrings

breakSubstring

Arguments

:: 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)

findSubstring

Arguments

:: ByteString | String to search for.
-> ByteString | String to seach in.
-> Maybe Int |

Deprecated: findSubstring is deprecated in favour of breakSubstring.

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)`.

findSubstrings

Arguments

:: ByteString | String to search for.
-> ByteString | String to seach in.
-> [Int] |

Deprecated: findSubstrings is deprecated in favour of breakSubstring.

Find the indexes of all (possibly overlapping) occurances of a substring in a string.

# Searching ByteStrings

## Searching by equality

elem :: Char -> ByteString -> Bool

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

notElem :: Char -> ByteString -> Bool

O(n) `notElem` is the inverse of `elem`

## Searching with a predicate

find :: (Char -> Bool) -> ByteString -> Maybe Char

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.

filter :: (Char -> Bool) -> ByteString -> ByteString

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

# Indexing ByteStrings

index :: ByteString -> Int -> Char

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

elemIndex :: Char -> ByteString -> Maybe Int

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.

elemIndices :: Char -> ByteString -> [Int]

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

elemIndexEnd :: Char -> ByteString -> Maybe Int

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)

findIndex :: (Char -> Bool) -> ByteString -> Maybe Int

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

findIndices :: (Char -> Bool) -> ByteString -> [Int]

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

count :: Char -> ByteString -> Int

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.

# Zipping and unzipping ByteStrings

zip :: ByteString -> ByteString -> [(Char, Char)]

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

zipWith :: (Char -> Char -> a) -> ByteString -> ByteString -> [a]

`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.

unzip :: [(Char, Char)] -> (ByteString, ByteString)

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

# Ordered ByteStrings

sort :: ByteString -> ByteString

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

# Reading from ByteStrings

readInt :: ByteString -> Maybe (Int, ByteString)

readInt reads an Int 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 int read, and the rest of the string.

readInteger :: ByteString -> Maybe (Integer, ByteString)

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 int read, and the rest of the string.

# Low level CString conversions

## Copying ByteStrings

copy :: ByteString -> ByteString

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.

## Packing CStrings and pointers

packCString :: CString -> IO ByteString

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.

packCStringLen :: CStringLen -> IO ByteString

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.

## Using ByteStrings as CStrings

useAsCString :: ByteString -> (CString -> IO a) -> IO a

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).

useAsCStringLen :: ByteString -> (CStringLen -> IO a) -> IO a

O(n) construction Use a `ByteString` with a function requiring a `CStringLen`. As for `useAsCString` this function makes a copy of the original `ByteString`.

# I/O with `ByteString`s

ByteString I/O uses binary mode, without any character decoding or newline conversion. The fact that it does not respect the Handle newline mode is considered a flaw and may be changed in a future version.

## Standard input and output

getLine :: IO ByteString

Read a line from stdin.

getContents :: IO ByteString

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

putStr :: ByteString -> IO ()

Write a ByteString to stdout

putStrLn :: ByteString -> IO ()

Write a ByteString to stdout, appending a newline byte

interact :: (ByteString -> ByteString) -> IO ()

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.

## Files

readFile :: FilePath -> IO ByteString

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.

writeFile :: FilePath -> ByteString -> IO ()

Write a `ByteString` to a file.

appendFile :: FilePath -> ByteString -> IO ()

Append a `ByteString` to a file.

## I/O with Handles

hGetLine :: Handle -> IO ByteString

Read a line from a handle

hGetContents :: Handle -> IO ByteString

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.

hGet :: Handle -> Int -> IO ByteString

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.

`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 :: Handle -> Int -> IO ByteString

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`.

hPut :: Handle -> ByteString -> IO ()

Outputs a `ByteString` to the specified `Handle`.

hPutNonBlocking :: Handle -> ByteString -> IO ByteString

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`.

hPutStr :: Handle -> ByteString -> IO ()

A synonym for `hPut`, for compatibility

hPutStrLn :: Handle -> ByteString -> IO ()

Write a ByteString to a handle, appending a newline byte