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 with either the trunk or dev version. Note that the trunk branch is updated infrequently and is currently almost two years behind!

Building and Running Hazel

Short version

If you already have ocaml version 5.0.0 and least version 2.0 of opam installed, you can build Hazel by running the following commands.

• git clone [email protected]:hazelgrove/hazel.git
• cd hazel
• make deps
• make dev

To view Hazel, you have to serve it, on localhost for development (you can't run it from a file:/// URL due to browser restrictions on web workers.)

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

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

Long Version

If you are unfamiliar with ocaml or opam, do not have them installed, or just get stuck, we recommend you follow the step-by-step installation instructions contained in INSTALL.md.

Contributing

From OCaml to ReasonML

This link lets you type OCaml and see what the corresponding ReasonML syntax is: https://reasonml.github.io/en/try.

This is useful if you are trying to figure out the ReasonML syntax for something that you know the OCaml syntax for.

Suggested Extensions for VS Code

Most of our team uses VisualStudio Code to write code. If you use VS Code, here are a few extensions that might be helpful.

• This extension provides full support for editing ReasonML source code and relevant tools:

  • ocaml-platform

• Due to Reason's poor parse errors, unbalanced parentheses can be difficult to find. The following extensions help with that.

  • Bracket Pair Colorizer 2
  • Indenticator
  • indent-rainbow

In addition to these extensions, enabling the breadcrumbs bar can make navigating a large code base easier. There are multiple ways to make the breadcrumbs bar visible:

• Click View / Show Breadcrumbs from the menu bar.
• Press Ctrl+Shift+P (macOS: Cmd+Shift+P), start typing breadcrumbs, and select View: Toggle Breadcrumbs from the dropdown menu to toggle breadcrumbs on and off.
• Press Ctrl+Shift+. to start breadcrumbs navigation.

Suggested Setup for NeoVim

If you enjoy your Vim binding and Vim setup, the following may help you set up your Reason IDE in NeoVim.

If you use vim, I recommend you to switch to NeoVim since it has a better support for multi-thread, and thus less likely to block you when you are programming.

To set up the LSP(Language Server Protocal), you need to set up your Language Client for Neovim and Language Server for ocaml.

• ocaml-language-server
• LanguageClient-neovim

After installing the previous two, you may want to copy the following to your neovim config file. (assuming npm have ocaml-language-server installed under /usr/bin)

let g:LanguageClient_serverCommands = {
    \ 'ocaml': ['/usr/bin/ocaml-language-server', '--stdio'],
    \ 'reason': ['/usr/bin/ocaml-language-server', '--stdio']
    \ }
" LanguageClient-neovim
nnoremap <F5> :call LanguageClient_contextMenu()<CR>
" Or map each action separately
nnoremap <silent> K :call LanguageClient#textDocument_hover()<CR>
nnoremap <silent> gd :call LanguageClient#textDocument_definition()<CR>
nnoremap <silent> gr :call LanguageClient#textDocument_references()<CR>
nnoremap <silent> gf :call LanguageClient#textDocument_formatting()<cr>
nnoremap <silent> <F2> :call LanguageClient#textDocument_rename()<CR>

Build System Details

Hazel is implemented in Reason (a dialect of OCaml) and is compiled to Javascript for the web browser via the js_of_ocaml compiler.

Though make targets are provided as a convenience, they mostly translate to dune commands.

Invoking make by itself is equivalent to invoking make dev. With these commands we pass additional flags to js_of_ocaml that cause the insertion of comments that map locations in the generated JS to locations in the source files. This is useful for debugging purposes.

make dev also auto-formats Reason source files using refmt (this is what the @src/fmt alias is for). This ensures code from all contributors follows the same style.

The make dev and make release commands do three things:

1. Generate some internal parsers using menhir.
2. Compile the Reason code to OCaml bytecode using the OCaml compiler.
3. Compile the OCaml bytecode to JavaScript (_build/default/src/hazelweb/www/hazel.js) using js_of_ocaml.

For a smoother dev experience, use make watch to automatically watch for file changes. This will require installing fswatch (see INSTALL.md). You can also run make watch-release to continuously build the release build (takes longer per build).

Clean Build

To obtain an clean build, you may need to:

• Clone the repository (if you have not), and enter the project root of your cloned Hazel project.

  git clone [email protected]:hazelgrove/hazel.git
  cd hazel

• Setup a local OCaml environment specific to the project, and compile. If you have setup a local OCaml environment (there is a directory called _opam), you may want to first remove it.

  # opam switch remove ./
  opam switch create ./ 5.0.0
  eval $(opam env)
  make deps
  make

This sets up a standalone OCaml environment in the cloned project, independent of the one you sent in your home directory. This allow you to alternate dependencies, or test dependencies changes, without affect existing OCaml projects.

Debugging

Printing

You can print to the browser console using the standard print_endline function. This is probably the easiest method right now.

Source Maps

js_of_ocaml does support source maps and has some other flags that might be useful. If you experiment with those and get them to work, please update this README with some notes.

Debug Mode

If Hazel is hanging on load or when you perform certain actions, you can load into Debug Mode by appending #debug to the URL and reloading. From there, you have some buttons that will change settings or reset local storage. Refresh without the #debug flag and hopefully you can resolve the situation from there.

Testing

You can run all of the unit tests located in src/hazelcore/test by running make test.

Unit tests are written using ppx_expect and ppx_inline_tests. If you would like to adjust your expect tests to assert for the output that was last printed, run make fix-test-answers.

If the inline test runner causes problems for you, you can likely resolve the issue by running opam update then opam upgrade.

Continuous Integration

When you push your branch to the main hazelgrove/hazel repository, we have a GitHub Action setup (see .github/workflows/deploy_branches.yml) that will build that branch (in release mode) and deploy it to the URL https://hazel.org/build/<branch name>, assuming the build succeeds.

It usually takes about 2 minutes if the build environment cache hits, or 20+ minutes if not. You can view the status of the build in the Actions tab on Github.