Contributing to Happy

Source Code Repository

Happy is hosted on GitHub. As previously discussed in `bug-reports`_, we use the built-in GitHub issue tracker for Happy. We also use GitHub pull requests for managing changes; feel free to submit them!

Repo Layout

  • src: The source code for the Happy executable itself

  • packages/*: The various packages that make up Happy behind the scenes, and are available for reuse for other purposes.

  • doc: The documentation

    This is in reStructured Text format as is common for many Haskell tools’ documentation. To build the documentation, use [Sphinx](

  • examples: Various examples of using Happy

Build Instructions

Happy is normal Cabal-packaged Haskell executable, except for the fact that a pre-built Happy is required to build the full version of Happy, which is the default.

  • If you do have an existing Happy executable on the PATH or in the default installation location (~/.cabal/bin for example), do regular

    $ cabal build

    like with any other project.

  • If you do not have an existing Happy executable, instead do

    $ cabal build -f -bootstrap
  • If you install that minimial, non-bootstrapped happy

    $ cabal install -f -bootstrap

    you can then build normally (with the bootstrap flag enabled).

We’re sorry the bootstrap process is a bit tedious right now; we hope to improve it in the future. The ideal fix would be to make cabal-installer’s cycle detector to be less pessimistic, per `<>`_, so that the build tool dependency can be properly expressed and everything works automatically.