Developing Hy

Contributor Guidelines

Contributions are welcome and greatly appreciated. Every little bit helps in making Hy better. Potential contributions include:

  • Reporting and fixing bugs.

  • Requesting features.

  • Adding features.

  • Writing tests for outstanding bugs or untested features.

    • You can mark tests that Hy can’t pass yet as xfail.

  • Cleaning up the code.

  • Improving the documentation.

  • Answering questions on the Github Discussions page or Stack Overflow.

  • Evangelizing for Hy in your organization, user group, conference, or bus stop.


In order to report bugs or request features, search the issue tracker to check for a duplicate. (If you’re reporting a bug, make sure you can reproduce it with the very latest, bleeding-edge version of Hy from the master branch on GitHub. Bugs in stable versions of Hy are fixed on master before the fix makes it into a new stable release.) If there aren’t any duplicates, then you can make a new issue.

It’s totally acceptable to create an issue when you’re unsure whether something is a bug or not. We’ll help you figure it out.

Use the same issue tracker to report problems with the documentation.

Pull requests

Submit proposed changes to the code or documentation as pull requests (PRs) on GitHub. Git can be intimidating and confusing to the uninitiated. This getting-started guide may be helpful. However, if you’re overwhelmed by Git, GitHub, or the rules below, don’t sweat it. We want to keep the barrier to contribution low, so we’re happy to help you with these finicky things or do them for you if necessary.

Deciding what to do

If you’re proposing a major change to the Hy language, or you’re unsure of the proposed change, create an issue to discuss it before you write any code. This will allow others to give feedback on your idea, and it can avoid wasted work.

Commit formatting

Many PRs are small enough that only one commit is necessary, but bigger ones should be organized into logical units as separate commits. PRs should be free of merge commits and commits that fix or revert other commits in the same PR (git rebase is your friend).

Avoid committing spurious whitespace changes.

Don’t commit comments tagged with things like “FIXME”, “TODO”, or “XXX”. Ideas for how the code or documentation should change go in the issues list, not the code or documentation itself.

The first line of a commit message should describe the overall change in 50 characters or less. If you wish to add more information, separate it from the first line with a blank line.


Tests can be run by executing pytest in the root of this repository.

New features and bug fixes should be tested. If you’ve caused an xfail test to start passing, remove the xfail mark. If you’re testing a bug that has a GitHub issue, include a comment with the URL of the issue.

No PR may be merged if it causes any tests to fail. The byte-compiled versions of the test files can be purged using git clean -dfx tests/. If you want to run the tests while skipping the slow ones in, use pytest --ignore=tests/


Generally, new features deserve coverage in the manual, either by editing the manual files directly or by changing docstrings that get included in the manual. To render the manual, install its dependencies with pip install -r requirements-dev.txt and then use the command cd docs; sphinx-build . _build -b html.


If you’re making user-visible changes to the code, add one or more items describing it to the NEWS file.

Finally, add yourself to the AUTHORS file (as a separate commit): you deserve it. :)

The PR itself

PRs should ask to merge a new branch that you created for the PR into hylang/hy’s master branch, and they should have as their origin the most recent commit possible.

If the PR fulfills one or more issues, then the body text of the PR (or the commit message for any of its commits) should say “Fixes #123” or “Closes #123” for each affected issue number. Use this exact (case-insensitive) wording, because when a PR containing such text is merged, GitHub automatically closes the mentioned issues, which is handy. Conversely, avoid this exact language if you want to mention an issue without closing it (because e.g. you’ve partly but not entirely fixed a bug).

There are two situations in which a PR is allowed to be merged:

  1. When it is approved by two members of Hy’s core team other than the PR’s author. Changes to the documentation, or trivial changes to code, need only one approving member.

  2. When the PR is at least three days old and no member of the Hy core team has expressed disapproval of the PR in its current state.

Anybody on the Hy core team may perform the merge. Merging should create a merge commit (don’t squash unnecessarily, because that would remove separation between logically separate commits, and don’t fast-forward, because that would throw away the history of the commits as a separate branch), which should include the PR number in the commit message. The typical workflow for this is to run the following commands on your own machine, then press the merge button on GitHub.

$ git checkout master
$ git pull
$ git checkout $PR_BRANCH
$ git fetch
$ get reset --hard $REMOTE/$PR_BRANCH
$ git rebase master
$ git push -f

Contributor Code of Conduct

As contributors and maintainers of this project, we pledge to respect all people who contribute through reporting issues, posting feature requests, updating documentation, submitting pull requests or patches, and other activities.

We are committed to making participation in this project a harassment-free experience for everyone, regardless of level of experience, gender, gender identity and expression, sexual orientation, disability, personal appearance, body size, race, ethnicity, age, or religion.

Examples of unacceptable behavior by participants include the use of sexual language or imagery, derogatory comments or personal attacks, trolling, public or private harassment, insults, or other unprofessional conduct.

Project maintainers have the right and responsibility to remove, edit, or reject comments, commits, code, wiki edits, issues, and other contributions that are not aligned to this Code of Conduct. Project maintainers who do not follow the Code of Conduct may be removed from the project team.

This code of conduct applies both within project spaces and in public spaces when an individual is representing the project or its community.

Instances of abusive, harassing, or otherwise unacceptable behavior may be reported by opening an issue or contacting one or more of the project maintainers.

This Code of Conduct is adapted from the Contributor Covenant, version 1.1.0, available at

Core Team

Hy’s core development team consists of the following people: