#+TITLE: Purescript layer

#+TAGS: general|js|layer|multi-paradigm|programming

[[file:img/purescript-logo.png]]

* Table of Contents                     :TOC_5_gh:noexport:
- [[#description][Description]]
  - [[#features][Features:]]
- [[#install][Install]]
- [[#configuration][Configuration]]
  - [[#add-import-on-completion][Add import on completion]]
  - [[#node-modules][Node Modules]]
  - [[#error-popup][Error popup]]
  - [[#lsp][LSP]]
- [[#key-bindings][Key bindings]]
  - [[#purescript][Purescript]]
    - [[#imports][Imports]]
    - [[#psc-ide][psc-ide]]
  - [[#repl][REPL]]

* Description
This layer provides basic Purescript editing support for spacemacs.

** Features:
- Syntax highlighting through [[https://github.com/dysinger/purescript-mode][purescript-mode]]
- Automatic insert of imports through [[https://github.com/epost/psc-ide-emacs][psc-ide-emacs]]
- REPL through [[https://github.com/ardumont/emacs-psci][psci]]
- Syntax checking through flycheck
- Autocompletion through company

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

You'll also need to make sure the PureScript compiler and its associated
binaries (psc-ide-server, psci,...) are on your path. Installation instructions
can be found [[https://github.com/purescript/documentation/blob/master/guides/Getting-Started.md][here]].

* Configuration
** Add import on completion
Set =purescript-add-import-on-completion= to nil to make =psc-ide= stop adding
imports on completion. Default value is =t=.

** Node Modules
If you would like =node_modules/.bin= to be automatically added to the buffer
local =exec_path=, e.g. to support project local purs/pulp installations, set the
=node-add-modules-path= variable in the =purescript= config section. Note that
doing this [[https://stackoverflow.com/questions/9679932#comment33532258_9683472][introduces a security risk]]:

#+BEGIN_SRC elisp
  (setq-default dotspacemacs-configuration-layers
    '((purescript :variables node-add-modules-path t)))
#+END_SRC

** Error popup
If you set =purescript-enable-rebuild-on-save= to non-nil, you will get a popup
buffer showing you your current warnings/errors one at a time. This is primarily
meant as an alternative to using flycheck. Default value is nil.

** 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 purescript 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
  (purescript :variables
          purescript-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 i -g purescript-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.

* Key bindings
** Purescript
*** Imports

| Key binding | Description                                                   |
|-------------+---------------------------------------------------------------|
| ~SPC m i =~ | Format imports                                                |
| ~SPC m i \~ | Return to where you were editing before navigating to imports |
| ~SPC m i a~ | Align imports                                                 |
| ~SPC m i n~ | Navigate to the imports                                       |

*** psc-ide

| Key binding   | Description                                                               |
|---------------+---------------------------------------------------------------------------|
| ~SPC m m s~   | Start psc-ide-server                                                      |
| ~SPC m m q~   | Quit the current psc-ide-server                                           |
| ~SPC m m l~   | Load definitions for the modules inside your project                      |
| ~SPC m m b~   | Rebuilds the current file and displays any warnings or errors             |
| ~SPC m m t~   | Add a new clause for the function signature at point                      |
| ~SPC m m c~   | Casesplits on the identifier at the current cursor position               |
| ~SPC m m L~   | Load a specific module (This is mostly used for troubleshooting)          |
| ~SPC m m i a~ | Add an import for the identifier at the current cursor position           |
| ~SPC m m i s~ | Inserts a suggestion for the warning/error at the current cursor position |
| ~SPC m h t~   | Show type at point                                                        |
| ~SPC m g g~   | Goto definition for identifier at point                                   |

** REPL
[[https://github.com/ardumont/emacs-psci][psci]] provides a very basic REPL for purescript. The following key
bindings are available:

| Key binding | Description                                                                      |
|-------------+----------------------------------------------------------------------------------|
| ~SPC m s b~ | Equivalent of =:m /path/to/current/module/file.purs= - Load <file> for importing |
| ~SPC m s i~ | Launch a psci console buffer                                                     |
| ~SPC m s m~ | Equivalent of =:i your.current.module.name= - Import <module> for use in PSCI    |
| ~SPC m s p~ | Load or reload files defined in the project file .psci                           |
