This part of the guide is specifically for maintainers, and outlines the development process and in particular, the branching strategy. We also point out Cloud Haskell’s various bits of infrastructure as they stand at the moment.

Perhaps the most important thing to do as a maintainer, is to make other developers aware of what you’re working on by assigning the github issue to yourself!


All releases are published to hackage. At some point we may start to make nightly builds available on this website. We need some help setting that up though.


We keep in touch through the parallel-haskell mailing list, and once you’ve joined the group, by posting to the mailing list address: This is a group for all things related to concurrent and parallel Haskell. There is also a maintainer/developer centric cloud-haskell-developers mailing list, which is more for in-depth questions about contributing to or maintaining Cloud Haskell.

You might also find some of us hanging out at #haskell-distributed on freenode from time to time.

We have a twitter account! @CloudHaskell will be used to make announcements (of new releases, etc) on a regular basis.

Bug/Issue Tracking and Continuous Integration

We report issues for each project in github. You can browse all issues without logging in, however to report new issues/bugs you will need to provide an email address and create an account.

If you have any difficulties doing so, please post an email to the parallel-haskell mailing list at

We currently use travis-ci for continuous integration. We do however, have an open source license for Atlassian Bamboo, which we will be migrating to over time - this process is quite involved so we don’t have a picture of the timescales yet.

Branching/Merging Policy

The master branch is the active development branch. Small changes can be committed directly to master, or committed to a branche before getting merged. When we’re ready to release, the project is tagged using the format vX.Y.Z once it has been published. Each release then gets its own release-x.y.z branch, created from the tagged commit. These can be used to produce interim/bug-fix releases if necessary.

A release tag should be of the form x.y.z and should not be prefixed with the repository name. Older tags use the latter form as they date from a time when all the Cloud Haskell source code lived under one git repository.

Patches should be made against master unless they represent an interim bug-fix to a given release-x-y-z branch. The latter should be created against the branch they intend to fix.

Development Branches

Development should usually take place on a feature-X or bugfix-Y branch. The old development branch is defunct and will be removed at some point in the future.

Interim and bug-fix only releases

The complexity around interim releases is necessary to deal with situations where we need to patch a release, but master has already moved on, making the patch irrelevant for the next major release. For example, assuming a project is at version 1.2.3 and we find a bug in module Foo.hs. Users who’re on v1.2.3 will want the fix asap for any production deployments, yet Foo.hs has been completely re-written/replaced on master and the bugfix isn’t needed there. To support user’s who do not wish to wait for v2.0.0 to be released, we create a release-1.2.4 branch and merge the bugfix into that, but we do not merge this back into master, since the patch won’t apply. This way, subsequent bug fixes to the 1.2.x series can also continue in parallel with changes to master if necessary.

What happens if we have a patch for release-1.2.3 that is applicable to master, but won’t apply cleanly due to changes since the release was tagged? In this situation, we create a bug-fix release branch as usual, into which the patch is merged. A maintainer will then have to retro-fit the patch so that it can be applied to master. This is a somewhat ugly, since if we wish to create subsequent bug-fixes and create another 1.2.5 branch (viz the example above), we’ll may have to manually transplant some changes from master in the process.

Keeping History

Try to make only clean commits, so that bisect will continue to work. At the same time, it can be helpful to avoid making destructive updates. If you’re planning on doing lots of squashes, then work in a branch and don’t commit directly to master until you’re finished and ready to QA and merge.

Committing without triggering CI builds

Whilst we’re on travis-ci, you can do this by putting the text [ci skip] anywhere in the commit message. Please, please do not put this on the first line of the commit message.

Once we migrate to Bamboo, this may change.

Follow the Contributing guidelines

What’s good for the goose…

Making API documentation available on the website

There is an open ticket to set up nightly builds, which will update the HEAD haddocks (on the website) and produce an ‘sdist’ bundle and add that to the website too.

See for details.

Release Process

First of all, a few prior warnings. Do not tag any projects until after you’ve finished and uploaded the release. If you build and tag three projects, only to find that a subsequent dependent package needs a bit of last minute surgery, you’ll be sorry you didn’t wait. With that in mind….

Before releasing any source code, make sure that all the github tickets added to the release are either resolved or remove them from the release if you’ve decided to exclude them.

First, make sure all the version numbers and dependencies are aligned.

  • bump the version numbers for each project that is being released
  • bump the dependency versions across each project if needed
  • make sure you’ve run a complete integration build and everything still installs ok
  • bump the dependency version numbers in the cloud-haskell meta package

Now you’ll want to go and update the change log and release notes for each project. Change logs are stored in the individual project’s git repository, whilst release notes are stored on the wiki. This is easy to forget, as I discovered! Change logs should be more concise than full blown release notes.

Generate the packages with cabal sdist and test them all locally, then upload them to hackage. Don’t forget to upload the cloud-haskell meta-package too!

After the release

Now you should tag all the projects with the relevant version number. Since moving to individual git repositories, the tagging scheme is now x.y.z and not <project>-x.y.z. Once you’ve tagged the release, create a branch named release-x.y.z and push both the newly created tag(s) and the branch(es).

Once the release is out, you should go to github and close all the tickets for the release.

After that, it’s time to tweet about the release, post to the parallel-haskell mailing list, blog etc. Spread the word.