Fast combinator parsing for bytestrings and text

Version on this page:
LTS Haskell 20.23:0.14.4@rev:3
Stackage Nightly 2023-06-04:0.14.4@rev:3
Latest on Hackage:0.14.4@rev:3

See all snapshots attoparsec appears in

BSD-3-Clause licensed and maintained by Bryan O'Sullivan
This version can be pinned in stack with:attoparsec-,3979

Module documentation for

  • Data
    • Data.Attoparsec
      • Data.Attoparsec.ByteString
        • Data.Attoparsec.ByteString.Char8
        • Data.Attoparsec.ByteString.Lazy
      • Data.Attoparsec.Char8
      • Data.Attoparsec.Combinator
      • Data.Attoparsec.Lazy
      • Data.Attoparsec.Number
      • Data.Attoparsec.Text
        • Data.Attoparsec.Text.Lazy
      • Data.Attoparsec.Types
      • Data.Attoparsec.Zepto

Welcome to attoparsec

attoparsec is a fast Haskell parser combinator library, aimed particularly at dealing efficiently with network protocols and complicated text/binary file formats.

Join in!

I’m happy to receive bug reports, fixes, documentation enhancements, and other improvements.

Please report bugs via the github issue tracker.

Master git repository:

  • git clone git://

There’s also a Mercurial mirror:

  • hg clone

(You can create and contribute changes using either Mercurial or git.)


This library is written and maintained by Bryan O’Sullivan,


  • Now compatible with GHC 7.9

  • Reintroduced the Chunk class, used by the parsers package

  • A new internal representation makes almost all real-world parsers faster, sometimes by big margins. For example, parsing JSON data with aeson is now up to 70% faster. These performance improvements also come with reduced memory consumption and some new capabilities.

  • The new match combinator gives both the result of a parse and the input that it matched.

  • The test suite has doubled in size. This made it possible to switch to the new internal representation with a decent degree of confidence that everything was more or less working.

  • The benchmark suite now contains a small family of benchmarks taken from real-world uses of attoparsec.

  • A few types that ought to have been private now are.

  • A few obsolete modules and functions have been marked as deprecated. They will be removed from the next major release.

  • The new Chunk typeclass allows for some code sharing with Ed Kmett’s parsers package:

  • New function runScanner generalises scan to return the final state of the scanner as well as the input consumed.

  • New dependency: the scientific package. This allows us to parse numbers much more efficiently.

  • peekWord8’, peekChar’: new primitive parsers that allow single-character lookahead.