# `streamly-bytestring`
Library for streamly and bytestring interoperation.
## Description
This package provides `Streamly.External.ByteString` and
`Streamly.External.ByteString.Lazy`.
### Strict ByteString
`Streamly.External.ByteString` provides functions to for
interoperation between streamly and strict bytestring.
`fromArray` and `toArray` are used to efficiently convert between
streamly's pinned array type (`Streamly.Memory.Array`) and bytestring.
`read`, `writeN` and `write` are `Unfold`s & `Fold`s provided by streamly
that are used to create and consume a stream of `Word8`. `writeN` is more
efficient than `write` and should be preferred over `write` when possible.
### Lazy Bytestring
`Streamly.External.ByteString.Lazy` provides functions to for
interoperation between streamly and lazy bytestring.
`readChunks` and `read` are `Unfold`s. `unfold` from `Streamly.Prelude` can be
used to create a stream of `Array Word8` or a stream of `Word8` from a
lazy `ByteString`.
`toChunks` is defined as `unfold readChunks`. `fromChunks` can be used to create a
lazy `ByteString` from a stream of `Array Word8` chunks.
## Usage
This is a dumb program that counts the number of bytes in a file.
```
import Streamly
import qualified Streamly.Prelude as S
import qualified Data.ByteString as BS
import qualified Data.ByteString.Lazy as BSL
import qualified Streamly.External.ByteString as Strict
import qualified Streamly.External.ByteString.Lazy as Lazy
import System.IO (FilePath)
strictByteStringSize :: BS.ByteString -> IO Int
strictByteStringSize bs = S.length $ S.unfold Strict.read bs
lazyByteStringSize :: BSL.ByteString -> IO Int
lazyByteStringSize bsl = S.foldl' (+) 0
$ S.mapM strictByteStringSize
$ S.map Strict.fromArray
$ Lazy.toChunks bsl
fileSize :: FilePath -> IO Int
fileSize path = do
bsl <- BSL.readFile path
lazyByteStringSize bsl
```