A Haskell library for efficient, concurrent, and concise data access.


Version on this page:
LTS Haskell 14.27:
Stackage Nightly 2019-09-21:
Latest on Hackage:

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LicenseRef-OtherLicense licensed by Facebook, Inc.
Maintained by The Haxl Team
This version can be pinned in stack with:haxl-,3157

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Haxl is a Haskell library that simplifies access to remote data, such as databases or web-based services. Haxl can automatically

  • batch multiple requests to the same data source,
  • request data from multiple data sources concurrently,
  • cache previous requests.

Having all this handled for you behind the scenes means that your data-fetching code can be much cleaner and clearer than it would otherwise be if it had to worry about optimizing data-fetching. We’ll give some examples of how this works in the pages linked below.

There are two Haskell packages here:

  • haxl: The core Haxl framework
  • haxl-facebook (in example/facebook): An (incomplete) example data source for accessing the Facebook Graph API

To use Haxl in your own application, you will likely need to build one or more data sources: the thin layer between Haxl and the data that you want to fetch, be it a database, a web API, a cloud service, or whatever. The haxl-facebook package shows how we might build a Haxl data source based on the existing fb package for talking to the Facebook Graph API.

Where to go next?

Build Status


Changes in version

  • ‘pAnd’ and ‘pOr’ were added
  • ‘asyncFetchAcquireRelease’ was added
  • ‘cacheResultWithShow’ was exposed
  • GHC 8.2.1 compatibility

Changes in version

  • Rename ‘Show1’ to ‘ShowP’ (#62)

Changes in version

  • Some performance improvements, including avoiding quadratic slowdown with left-associated binds.

  • Documentation cleanup; Haxl.Core is the single entry point for the core and engine docs.

  • (>>) is now defined to be (*>), and therefore no longer forces sequencing. This can have surprising consequences if you are using Haxl with side-effecting data sources, so watch out!

  • New function withEnv, for running a sub-computation in a local Env

  • Add a higher-level memoization API, see ‘memo’

  • Show is no longer required for keys in cachedComputation

  • Exceptions now have Eq instances