Hazel

Hazel is a live functional programming environment rooted in the principles of type theory. You can find the relevant papers and more motivation at the Hazel website.

You can try Hazel online: the dev branch is the main branch at the moment. Every other branch that has been pushed to GitHub and successfully builds can also be accessed at:

https://hazel.org/build/<branch_name>

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Building Hazel

Short version

If you already have ocaml version 5.2.0, at least version 2.0 of opam, and a recent version of npm installed, and you have your GitHub SSH keys set up, you can build Hazel by running the following commands.

• git clone git@github.com:hazelgrove/hazel.git
• cd hazel
• make deps
• make dev

Long Version

If the above pre-requisites don't apply, please follow the step-by-step installation instructions contained in INSTALL.md.

Build Warnings

You may see the following harmless warnings when building.

Ezjs_idb

Warning 58 [no-cmx-file]: no cmx file was found in path for module Ezjs_idb, and its interface was not compiled with -opaque

This is due to an upstream library issue and can be ignored.

joo_global_object

'joo_global_object' is being deprecated, please use `globalThis` instead

This is due various upstream library issues and can be ignored.

Running Hazel

Locally

To run Hazel, you have to serve it on localhost or at some other non-file URL (you can't run it from a file:/// URL due to browser restrictions e.g. on web workers.)

If you have python3 on your path, you can use the built in Python server via make serve, then navigate to http://0.0.0.0:8000/ in your browser.

Alternatively, if you would live hot reloading, you can use make hot instead of make serve.

Otherwise, run make echo-html-dir which will echo the directory that needs to be served using some other server of your choice.

Build Server

Every branch that has been pushed to GitHub and successfully builds can also be accessed at the following URL (once the GitHub action is finished building and deploying it):

https://hazel.org/build/<branch_name>

Hazel CLI

Although Hazel is primarily designed as an integrated development environment, we do have a Hazel CLI executable called hazel available for basic tasks at the terminal. Further information is available in the CLI README.

Running Tests

You can run Hazel's unit tests with make test. Further details on testing are in the test README.

Contributing to Hazel

We welcome open source contributions to Hazel! If you are planning to contribute, please review the information in CONTRIBUTING.md, which details how to run tests. You may also want to contact Cyrus Omar (comar@umich.edu) about your plans. We have a team Slack that might be helpful for you to join if you are planning to make non-trivial contributions and are happy to invite (and assist) external contributors!