Snap: A Haskell Web Framework (core interfaces and types)

Version on this page:
LTS Haskell 8.6:
Stackage Nightly 2017-03-28:
Latest on Hackage:
BSD3 licensed by Snap Framework Authors (see CONTRIBUTORS)
Maintained by

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Snap Framework Core

Build Status

Snap is a web framework for Haskell. For more information about Snap, read the or visit the Snap project website at

Library contents

This is the snap-core library, which contains:

  • primitive types and functions for HTTP (requests, responses, cookies, post/query parameters, etc).

  • a "Snap" monad interface for programming web handlers, which allows:

    • stateful access to the HTTP request and response objects.

    • monadic failure (i.e. MonadPlus/Alternative instances) for declining to handle requests and chaining handlers together.

    • early termination of the computation if you know early what you want to return and want to prevent further monadic processing.

  • useful utilities for web handlers, like file serving and gzip/zlib compression.

Building snap-core

The snap-core library is built using Cabal and Hackage. Just run

cabal install

from the snap-core toplevel directory.

Building the Haddock Documentation

The haddock documentation can be built using the supplied shell script:


The docs get put in dist/doc/html/.

Building the testsuite

Snap aims for 100% test coverage, and we're trying hard to stick to that.

To build the test suite, configure with --enable-tests:

$ cabal configure --enable-tests
$ cabal build

From here you can invoke the testsuite by running:

$ ./

The testsuite generates an hpc test coverage report in dist/hpc.

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