#+TITLE: Elm layer

#+TAGS: general|layer|programming|pure

[[file:img/elm.png]]

* Table of Contents                     :TOC_5_gh:noexport:
- [[#description][Description]]
  - [[#features][Features:]]
- [[#install][Install]]
  - [[#layer][Layer]]
  - [[#elm-platform][Elm Platform]]
    - [[#macos-and-windows-installers][macOS and Windows installers]]
    - [[#universal-installer-using-npm][Universal installer using npm]]
    - [[#source-code][Source code]]
  - [[#elm-format][elm-format]]
  - [[#elm-test][elm-test]]
- [[#configuration][Configuration]]
  - [[#choosing-a-backend][Choosing a backend]]
    - [[#company-elm][Company-elm]]
      - [[#elm-oracle][elm-oracle]]
    - [[#lsp][LSP]]
- [[#basic-usage-tips][Basic usage tips]]
  - [[#compilation][Compilation]]
  - [[#reactor][Reactor]]
  - [[#on-save-usage][On save usage]]
    - [[#imports-sort][Imports sort]]
    - [[#file-format][File format]]
  - [[#indentation][Indentation]]
  - [[#test-runner-settings][Test runner settings]]
- [[#key-bindings][Key bindings]]
  - [[#elm-make][elm-make]]
  - [[#elm-repl][elm-repl]]
  - [[#elm-reactor][elm-reactor]]
  - [[#elm-test-runner][elm-test-runner]]
  - [[#elm-package][elm-package]]
    - [[#package-list-buffer][package list buffer]]
  - [[#elm-oracle-1][elm-oracle]]
  - [[#elm-format-1][elm-format]]
  - [[#refactoring][Refactoring]]

* Description
This layer adds support for [[http://elm-lang.org][Elm]].

It relies on [[https://github.com/jcollard/elm-mode][elm-mode]] and [[https://github.com/bsermons/flycheck-elm][flycheck-elm]].

** Features:
- Syntax highlighting.
- Intelligent indentation
- Auto-completion integration for company (default) or auto-complete modes
- Syntax checking support using flycheck
- Integration with elm-make
- Integration with elm-repl
- Integration with elm-reactor
- Integration with elm-package

* Install
** Layer
To use this configuration layer, add it to your =~/.spacemacs=. You will need to
add =elm= to the existing =dotspacemacs-configuration-layers= list in this
file.

** Elm Platform
The =elm-platform= is a bundle of tools, including the =elm-compiler=,
=elm-make=, =elm-reactor=, =elm-repl= and =elm-package=.

Depending on the method of installation, the =elm-mode= package would need to be
able to access commands such as =elm-reactor= or =elm-make=.

*** macOS and Windows installers
Official installers for these operating systems are available from:
[[https://guide.elm-lang.org/install.html][https://guide.elm-lang.org/install.html]]

*** Universal installer using npm
A npm based installer is available to, and provides pre-compiled binaries for
certain operating system and architectures.

#+BEGIN_SRC sh
  npm install --global elm
#+END_SRC

Also, note that you might need to set the =ELM_HOME= environment variables to
the corresponding directory created by the installer.

If you are facing problems with previewing a buffer with =elm-reactor= ensure
that the absolute path of the npm global bin file is on your path within emacs

MacOS users facing problems with =elm-reactor= failing to properly install or
run, see this issue [[https://github.com/kevva/elm-bin/issues/28][https://github.com/kevva/elm-bin/issues/28]].

*** Source code
To build from source, see instructions here:
[[https://github.com/elm-lang/elm-platform][https://github.com/elm-lang/elm-platform]]

** elm-format
=elm-format= can be used to format elm code according to a standard set of
rules.

To install =elm-format= run below command:

#+BEGIN_SRC sh
  npm install --global elm-format
#+END_SRC

If this does not work for you please check [[https://github.com/avh4/elm-format][here]].

Also, note that if you use homebrew to install =elm-format= the installed exe
has a version suffix, the installed command name can be set in your
=~/spacemacs=:

#+BEGIN_SRC emacs-lisp
  (elm :variables
       elm-format-command "elm-format-0.17")
#+END_SRC

** elm-test
=elm-test= can be used to run unit tests.

To install =elm-test= run below command:

#+BEGIN_SRC sh
  npm install --global elm-test
#+END_SRC

* Configuration
All layer configurations can be done by setting layer variables in your dotfile.
No custom user config lines are necessary

** Choosing a backend
This layer provides two alternative backends to choose from.

*** Company-elm
This is the default choice if nothing is set and no lsp layer
is loaded in your dotfile. This mode only provides very
limited IDE capabilities. Used best if only small programs
are edited. To set explicitly set the following in your
dotfile:

#+BEGIN_SRC emacs-lisp
  (elm :variables elm-backend 'company-elm)
#+END_SRC

**** elm-oracle
=elm-oracle= can be used to show type signatures and docs for tokens under the
cursor and provide support for auto-completion, but it is not part of the
standard elm-platform.

Both the "company" and "auto-complete" backends are supported, but this layer
is configured with company.

To install =elm-oracle=, install =node.js= and =npm=, then
run this command:

#+BEGIN_SRC sh
  npm install -g elm-oracle
#+END_SRC

*** LSP
For proper IDE support this backend should be used. It is
based on an external server which will be started automatically
by emacs, once an elm file is opened. The key bindings are
the same for all lsp modes so if you are already familiar with
one you should be able to work the same in all modes.

To set explicitly do the following in your dotfile:

#+BEGIN_SRC emacs-lisp
  (elm :variables
          elm-backend 'lsp)
#+END_SRC

For this to work you will also need to install
the lsp server and separate dependencies with below
command:

#+BEGIN_SRC sh
  npm install -g elm-analyse @elm-tooling/elm-language-server
#+END_SRC

NOTE: Key bindings for LSP are defined in the
LSP layer. Also it is advisable to have a look
at the autocomplete layer for an optimal
intellisense config for LSP.

* Basic usage tips
** Compilation
To control the name of the compiled JavaScript file, use ~SPC m c B~ instead of
~SPC m c b~. This will overwrite the =--output= parameter of =elm-make= to
=[buffer-name].js= instead of the default.

** Reactor
=elm-reactor= is an interactive development tool, used to develop and debug Elm
programs. It will automatically compile an Elm program, and run it in the
browser, with editor agnostic support for hot-swapping and time-travel
debugging.

To preview =Main.elm=, press ~C-c C-m~ (or ~SPC m R m~).
Alternatively, to preview from buffer, press ~C-u C-c C-n~ (or ~SPC m R
n~). To preview in debug mode, prefix with ~C-u~ (or ~SPC u~).

By default, =elm-reactor= with launch with its own generated index.html. To use
a custom html, you'd need to load the debuger excplictly and use an http daemon
to serve your custom file.

If needed, default values for host and port used by for the elm-reactor server
can be controlled by passing in these variables in your =~/.spacemacs=:

#+BEGIN_SRC emacs-lisp
  (elm :variables
       elm-reactor-port "3000"          ; default 8000
       elm-reactor-address "0.0.0.0") ; default 127.0.0.1
#+END_SRC

** On save usage
*** Imports sort
Set =elm-sort-imports-on-save= to =t= to sort the imports in the current file on
every save.

#+BEGIN_SRC emacs-lisp
  (elm :variables elm-sort-imports-on-save t)
#+END_SRC

*** File format
Set =elm-format-on-save= to =t= to format current file on every save.

#+BEGIN_SRC emacs-lisp
  (elm :variables elm-format-on-save t)
#+END_SRC

** Indentation
elm-mode indentation is based on cycling: every time you insert a new line there
will be one or more indentation levels available for you to choose from. The
exact number is printed in the minibuffer either as Sole indentation or Indent
cycle (n)... where n is the number of available indentations to choose from. If
the automatic indentation level was not the one you expected simply hit TAB to
cycle through the list (note that hitting any other key will cancel the cycle).

** Test runner settings
You may want to customize the default suffix for test files. For example, if you
prefer to put your tests in =HelloSpec.elm= instead of =HelloTest.elm=, set the
following variable:

#+BEGIN_SRC emacs-lisp
  (elm :variables
       elm-test-runner-preferred-test-suffix "Spec")
#+END_SRC

Take a look [[https://github.com/juanedi/elm-test-runner#customization][here]] for more settings, and remember that this can be set by project
using a =dir-locals.el= file.

* Key bindings
** elm-make

| Key binding | Description                                  |
|-------------+----------------------------------------------|
| ~SPC m c b~ | elm-compile-buffer                           |
| ~SPC m c B~ | spacemacs/elm-compile-buffer-override-output |
| ~SPC m c m~ | elm-compile-main                             |

** elm-repl

| Key binding | Description                                                |
|-------------+------------------------------------------------------------|
| ~SPC m s i~ | elm-repl-load                                              |
| ~SPC m s f~ | send current function to REPL                              |
| ~SPC m s F~ | send current function to REPL and focus it in insert state |
| ~SPC m s r~ | send current region to REPL                                |
| ~SPC m s R~ | send current region to REPL and focus it in insert state   |

** elm-reactor

| Key binding | Description        |
|-------------+--------------------|
| ~SPC m R n~ | elm-preview-buffer |
| ~SPC m R m~ | elm-preview-main   |

** elm-test-runner

| Key binding   | Description                            |
|---------------+----------------------------------------|
| ~SPC m t b~   | elm-test-runner-run                    |
| ~SPC m t d~   | elm-test-runner-run-directory          |
| ~SPC m t p~   | elm-test-runner-run-project            |
| ~SPC m t r~   | elm-test-runner-rerun                  |
| ~SPC m t w~   | elm-test-runner-watch                  |
| ~SPC m t TAB~ | elm-test-runner-toggle-test-and-target |

** elm-package

| Key binding | Description              |
|-------------+--------------------------|
| ~SPC m p i~ | elm-import               |
| ~SPC m p c~ | elm-package-catalog      |
| ~SPC m p d~ | elm-documentation-lookup |

*** package list buffer

| Key binding | Description         |
|-------------+---------------------|
| ~g~         | elm-package-refresh |
| ~v~         | elm-package-view    |
| ~m~         | elm-package-mark    |
| ~u~         | elm-package-unmark  |
| ~x~         | elm-package-install |
| ~q~         | quit-window         |

** elm-oracle

| Key binding | Description              |
|-------------+--------------------------|
| ~SPC m h h~ | elm-oracle-doc-at-point  |
| ~SPC m h t~ | elm-oracle-type-at-point |

** elm-format

| Key binding | Description            |
| ~SPC m = b~ | elm-mode-format-buffer |

** Refactoring

| Key binding | Description      |
|-------------+------------------|
| ~SPC m r i~ | elm-sort-imports |
