elm-format

elm-format is still in alpha. If you run into any problems, please report them.

The format produced by elm-format may change significantly before the 1.0.0 release. If this will cause problems for you, please refrain from using elm-format during the alpha- and beta-test periods.

elm-format formats Elm source code according to a standard set of rules. It is inspired by the popular gofmt.

The benefits of elm-format:

• It makes code easier to write, because you never have to worry about minor formatting concerns while powering out new code.
• It makes code easier to read, because there are no longer distracting minor stylistic differences between different code bases. As such, your brain can map more efficiently from source to mental model.
• It makes code easier to maintain, because you can no longer have diffs related only to formatting; every diff necessarily involves a material change.
• It saves your team time debating how to format things, because there is a standard tool that formats everything the same way.

Usage

elm-format Main.elm  # Format a single file
elm-format Main.elm --yes  # Overwrite the file without prompting
elm-format src/  # Format all *.elm files in a directory
elm-format --stdin  # Format input from stdin and write to stdout
elm-format --stdin --output Main.elm  # Format input from stdin and write to file
elm-format --help  # See other command line options

Installation

elm-format is still in alpha. If you run into any problems, please report them.

The format produced by elm-format may change significantly before the 1.0.0 release. If this will cause problems for you, please refrain from using elm-format during the alpha- and beta-test periods.

You will need to download the version appropriate for your OS, unzip it, and place elm-format or elm-format.exe (windows) on your PATH. Simpler installation options will be available once there is a stable release of elm-format.

If you need PGP signatures, see the releases page.

For Elm 0.17

(Using this version with Elm 0.16 files will migrate them to Elm 0.17 syntax.)

• Mac: download
• Linux: download
• Windows: download

For Elm 0.16

• Mac: download
• Linux: download
• Windows: download

Editor integration

Find your editor in the table below. The recommended plugin for each editor is indicated with 🏆 (trophy emoji).

Editor	Plugin	Installation	Formatting	Format on save	Configuration	Error handling
Atom	🏆 atom-elm-format	✅ 2 steps	❔ TBD	✅	❔ TBD	❔ TBD
	atom-beautify	⚠️ 3 steps	❔ TBD	⚠️ requires configuration	❔ TBD	❔ TBD
Light Table	🏆 elm-light	⚠️ 3 steps	❔ TBD	⚠️ requires configuration	❔ TBD	❔ TBD
Vim	🏆 elm-vim	❌ 4 steps	❔ TBD	⚠️ requires configuration	❔ TBD	❔ TBD
Emacs	🏆 elm-mode	⚠️ 3 steps	❔ TBD	⚠️ requires configuration	❔ TBD	❔ TBD
Visual Studio Code	🏆 Elm Language Support	⚠️ 3 steps	❔ TBD	❌	❔ TBD	❔ TBD
	VSCode Elm Format	⚠️ 3 steps	❔ TBD	⚠️ requires configuration	❔ TBD	❔ TBD
Sublime Text	🏆 Elm Language Support	✅ 2 steps	❔ TBD	✅	❔ TBD	❔ TBD

Detailed instructions

If you can simplify or improve the installation instructions or add instructions for another editor, please make a pull request. The default behavior of elm-format-approved plugins is to format Elm files on save.

atom-elm-format installation

1. Install elm-format

2. Install atom-elm-format

   apm install atom-elm-format
   

or use the Atom package manager in Atom's settings

atom-beautify installation

1. Install elm-format

2. Install atom-beautify

   apm install atom-beautify
   

or use the Atom package manager in Atom's settings

1. Use ^⌥B (CTRL-ALT-B) to format a file

elm-light installation

1. Install elm-format
2. Install the elm-light plugin using the Light Table plugin manager
3. Add the following to your user keymap:

[:editor.elm "ctrl-s" :save :elm-format :elm.lint]

This step needs improvement to be understandable by novice Light Table users: how does one edit the user keymap?

elm-mode installation

1. Install elm-format

2. Install elm-mode (official instructions)

   If your Emacs has package.el (which is automatically the case for Emacs >= 24), you can install elm-mode from the package in MELPA.

   This step needs improvement to be understandable by novice Emacs users: how does one install a package from MELPA?

3. Use C-c C-f to format buffers (when in elm-mode)

4. Set or customize elm-format-on-save to t to apply elm-format on the current buffer on every save

   This step needs improvement to be understandable by novice Emacs users: how does one customize the elm-format-on-save setting?

See also the respective section about elm-format at elm-mode

elm-vim installation

1. Install elm-format

2. Install vim-plug (official instructions)

   curl -fLo ~/.vim/autoload/plug.vim --create-dirs \
       https://raw.githubusercontent.com/junegunn/vim-plug/master/plug.vim

3. Install elm-vim (official instructions)

   Add Plug 'elmcast/elm-vim to your plugin section

   This step needs improvement to be understandable by novice Vim users: where is the plugin section?

4. Add the following to your .vimrc file:

let g:elm_format_autosave = 1

Visual Studio Code installation

1. Install elm-format

2. Install Elm tools for VSCode

   ext install elm

3. SHIFT-ALT-F will format the current file

VSCode Elm Format installation

1. Install elm-format

2. Install VSCode Elm Format

   ext install elm-format

3. You can run elm-format by using the Elm: Format command

4. You can also run elm-format whenever you save the file by enabling the `formatOnSave' option

   This step needs improvement to be understandable by novice Visual Studio Code users: how does one enable the formatOnSave option?

Sublime Text installation

1. Install elm-format
2. Install the Elm Language Support package.

Development info

Building from source

git clone https://github.com/avh4/elm-format.git
cd elm-format
cabal sandbox init
cabal install --only-dependencies --enable-tests
cabal build
./dist/build/elm-format-0.17/elm-format-0.17 --help

Running tests

brew install shellcheck
cabal configure --enable-tests
./tests/run-tests.sh