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GHC 10.0.0.20260917 · lts/ghc-10.0.x · 8fef28d · 2026-11-02

Modulerio-0.1.25.0Haskell2010

RIO.ByteString.Lazy

Lazy ByteString. Import as:

import qualified RIO.ByteString.Lazy as BL

This module does not export any partial functions. For those, see RIO.ByteString.Lazy.Partial

Contents
  1. The ByteString type
  2. Introducing and eliminating ByteStrings
  3. Basic interface
  4. Transforming ByteStrings
  5. Reducing ByteStrings (folds)
  6. Special folds
  7. Building ByteStrings
  8. Scans
  9. Accumulating maps
  10. Infinite ByteStrings
  11. Unfolding ByteStrings
  12. Substrings
  13. Breaking strings
  14. Breaking into many substrings
  15. Predicates
  16. Search ByteStrings
  17. Searching by equality
  18. Searching with a predicate
  19. Indexing ByteStrings
  20. Zipping and unzipping ByteStrings
  21. Low level conversions
  22. Copying ByteStrings
  23. I/O with ByteStrings
  24. Standard input and output
  25. Files
  26. I/O with Handles
Synopsis
  • Packagerio-0.1.25.0
  • Exports85
  • LanguageHaskell2010
  • LicenceMIT
  • SourceLazy.hs

The ByteString type

datadata ByteString

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

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

Instances14IsList, Eq, Data, Ord, Read, Show, …
  • IsList ByteStringDefined in bytestring-0.12.2.0 · Data.ByteString.Lazy.Internal
  • Eq ByteStringDefined in bytestring-0.12.2.0 · Data.ByteString.Lazy.Internal
  • Data ByteStringDefined in bytestring-0.12.2.0 · Data.ByteString.Lazy.Internal
  • Ord ByteStringDefined in bytestring-0.12.2.0 · Data.ByteString.Lazy.Internal
  • Read ByteStringDefined in bytestring-0.12.2.0 · Data.ByteString.Lazy.Internal
  • Show ByteStringDefined in bytestring-0.12.2.0 · Data.ByteString.Lazy.Internal
  • IsString ByteStringDefined in bytestring-0.12.2.0 · Data.ByteString.Lazy.Internal

    Beware: fromString truncates multi-byte characters to octets. e.g. "枯朶に烏のとまりけり秋の暮" becomes �6k�nh~�Q��n�

  • Semigroup ByteStringDefined in bytestring-0.12.2.0 · Data.ByteString.Lazy.Internal
  • Monoid ByteStringDefined in bytestring-0.12.2.0 · Data.ByteString.Lazy.Internal
  • NFData ByteStringDefined in bytestring-0.12.2.0 · Data.ByteString.Lazy.Internal
  • Binary ByteStringDefined in binary-0.8.9.3 · Data.Binary.Class
  • Hashable ByteStringDefined in hashable-1.5.1.0 · Data.Hashable.Class
  • Lift ByteStringDefined in bytestring-0.12.2.0 · Data.ByteString.Lazy.Internal
  • type Item ByteString = Word8Defined in bytestring-0.12.2.0 · Data.ByteString.Lazy.Internal

Introducing and eliminating ByteStrings

Basic interface

O(1) Unlike cons, cons' is strict in the ByteString that we are consing onto. More precisely, it forces the head and the first chunk. It does this because, for space efficiency, it may coalesce the new byte onto the first 'chunk' rather than starting a new 'chunk'.

So that means you can't use a lazy recursive contruction like this:

let xs = cons' c xs in xs

You can however use cons, as well as repeat and cycle, to build infinite lazy ByteStrings.

Transforming ByteStrings

Reducing ByteStrings (folds)

valuefoldl :: (a -> Word8 -> 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.

valuefoldr :: (Word8 -> a -> a) -> a -> ByteString -> a

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.

Special folds

Building ByteStrings

Scans

valuescanl
  1. :: (Word8 -> Word8 -> Word8)

    accumulator -> element -> new accumulator

  2. -> Word8

    starting value of accumulator

  3. -> ByteString

    input of length n

  4. -> ByteString

    output of length n+1

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

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

Accumulating maps

valuemapAccumL
  1. :: acc -> Word8 -> (acc, Word8)
  2. -> acc
  3. -> ByteString
  4. -> (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 ByteString.

valuemapAccumR
  1. :: acc -> Word8 -> (acc, Word8)
  2. -> acc
  3. -> ByteString
  4. -> (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.

Infinite ByteStrings

Unfolding ByteStrings

valueunfoldr :: (a -> Maybe (Word8, a)) -> a -> ByteString

O(n) 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 a prepending to the ByteString and b is used as the next element in a recursive call.

Substrings

Breaking strings

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.

Breaking into many substrings

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

split 10  "a\nb\nd\ne" == ["a","b","d","e"]   -- fromEnum '\n' == 10
split 97  "aXaXaXa"    == ["","X","X","X",""] -- fromEnum 'a' == 97
split 120 "x"          == ["",""]             -- fromEnum 'x' == 120
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.

valuesplitWith :: (Word8 -> 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 (==97) "aabbaca" == ["","","bb","c",""] -- fromEnum 'a' == 97
splitWith undefined ""     == []                  -- and not [""]

Predicates

Search ByteStrings

Searching by equality

Searching with a predicate

valuefind :: (Word8 -> Bool) -> ByteString -> Maybe Word8

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

Indexing ByteStrings

valuecount :: Word8 -> ByteString -> Int64

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.

Zipping and unzipping ByteStrings

valuezip :: ByteString -> ByteString -> [(Word8, Word8)]

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.

Low level conversions

Copying ByteStrings

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.

I/O with ByteStrings

Standard input and output

Files

I/O with Handles