io-streams: Simple, composable, and easy-to-use stream I/O

[ bsd3, data, io-streams, library, network ] [ Propose Tags ]


The io-streams library contains simple and easy-to-use primitives for I/O using streams. Most users will want to import the top-level convenience module System.IO.Streams, which re-exports most of the library:

import           System.IO.Streams (InputStream, OutputStream)
import qualified System.IO.Streams as Streams

For first-time users, io-streams comes with an included tutorial, which can be found in the System.IO.Streams.Tutorial module.


The io-streams user API has two basic types: InputStream a and OutputStream a, and three fundamental I/O primitives:

-- read an item from an input stream :: InputStream a -> IO (Maybe a)

-- push an item back to an input stream
Streams.unRead :: a -> InputStream a -> IO ()

-- write to an output stream
Streams.write :: Maybe a -> OutputStream a -> IO ()

Streams can be transformed by composition and hooked together with provided combinators:

ghci> Streams.fromList [1,2,3::Int] >>= (*10) >>= Streams.toList

Stream composition leaves the original stream accessible:

ghci> input <- Streams.fromByteString "long string"
ghci> wrapped <- Streams.takeBytes 4 input
ghci> wrapped
Just "long"
ghci> wrapped
ghci> input
Just " string"

Simple types and operations in the IO monad mean straightforward and simple exception handling and resource cleanup using Haskell standard library facilities like Control.Exception.bracket.

io-streams comes with:

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Change log
Dependencies attoparsec (>=0.10 && <0.13), base (==4.*), blaze-builder (>=0.3.1 && <0.4), bytestring (>=0.9 && <0.11), network (>=2.3 && <2.7), primitive (>=0.2 && <0.6), process (>=1.1 && <1.3), text (>=0.10 && <1.3), time (>=1.2 && <1.6), transformers (>=0.2 && <0.5), vector (>=0.7 && <0.11), zlib-bindings (==0.1.*) [details]
License BSD-3-Clause
Maintainer Gregory Collins <>
Revised Revision 1 made by HerbertValerioRiedel at Thu Jan 1 09:29:15 UTC 2015
Category Data, Network, IO-Streams
Bug tracker
Source repo head: git clone
Uploaded by GregoryCollins at Sat Dec 6 20:41:43 UTC 2014
Distributions Arch:, Debian:, Fedora:, LTSHaskell:, NixOS:, Stackage:
Downloads 36010 total (648 in the last 30 days)
Rating 2.5 (votes: 3) [estimated by rule of succession]
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Status Docs uploaded by user
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Readme for io-streams-

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The io-streams library contains simple and easy to use primitives for I/O using streams. Based on simple types with one type parameter (InputStream a and OutputStream a), io-streams provides a basic interface to side-effecting input and output in IO monad with the following features:

  • three fundamental I/O primitives that anyone can understand: read :: InputStream a -> IO (Maybe a), unRead :: a -> InputStream a -> IO (), and write :: Maybe a -> OutputStream a -> IO ().

  • simple types and side-effecting IO operations mean straightforward and simple exception handling and resource cleanup using standard Haskell facilities like bracket.

  • code to transform files, handles, and sockets to streams

  • a variety of combinators for wrapping and transforming streams, including compression and decompression using zlib, controlling precisely how many bytes are read to or written from a socket, buffering output using blaze-builder, etc.

  • support for parsing from streams using attoparsec.