This post is part of a series. Related posts:

Creating a ReasonML Native App: What We Are Building
Creating a ReasonML Native App: Building and Running
Creating a ReasonML Native App: Command Line Arguments
Creating a ReasonML Native App: Configuration Files
Creating a ReasonML Native App: Curses Terminal Interface
Creating a ReasonML Native App: Python Plugins
Creating a ReasonML Native App: Files I/Os
Creating a ReasonML Native App: Native Promises
Creating a ReasonML Native App: Web Requests
Creating a ReasonML Native App: Shell Commands
Creating a ReasonML Native App: Handling CSV Files
Creating a ReasonML Native App: Native JSON Handling
Creating a ReasonML Native App: Memoizing DNS queries

Installing Reason

First, we will need OCaml. This is because our Reason code will be compiled to OCaml, then, using the OCaml compiler, to native code.

I would strongly recommend installing opam, rather than directly installing any distribution-native flavor of OCaml. The simplest way is using this bootstrap script:

wget https://raw.github.com/ocaml/opam/master/shell/opam_installer.sh -O - | sh -s /usr/local/bin

You can now simply update and install the desired version of OCaml. Right now, Reason works best with versions ~ 4.05:

opam update && opam switch 4.05.0

And finally reason and merlin, its completion tool:

opam install reason merlin

Configuring our favorite editor

If you happen to be in love with VSCode, you’are almost there. It’s definitely the editor that Reason’s authors seem to favor.

If you are more interested in the nitty gritty of a proper, clean install for native code, let’s have a look at my vim setup…

Our favorite editor is vim (today, anyway)

Note: recently, support for Reason was baked into OniVim. This makes it a very easy starting point! Check it out

First, you need to install the OCaml language server. I know a language server specific to Reason also exists, but again, that plugin may not perform as well w/r/t native OCaml integrations.

npm install -g ocaml-language-server

Yes,I know: Node, again, totally inescapable!

Now, let’s install our vim plugins: Language Support Client and vim-reason-plus – if you are using Vim-Plug (my favorite plugin manager) simply add these lines to your ~/.vimrc

Plug 'reasonml-editor/vim-reason-plus'
Plug 'autozimu/LanguageClient-neovim', {
\ 'branch': 'next',
\ 'do': 'bash install.sh',
\ }
...
autocmd BufReadPost *.re setlocal filetype=reason
...
let g:LanguageClient_loggingLevel = 'DEBUG'

let g:LanguageClient_serverCommands = {
    \ 'reason': ['ocaml-language-server', '--stdio'],
    \ 'ocaml': ['ocaml-language-server', '--stdio'],
    \ }
let g:LanguageClient_autoStart = 1

nnoremap <silent> gd :call LanguageClient_textDocument_definition()<cr>
nnoremap <silent> gf :call LanguageClient_textDocument_formatting()<cr>
nnoremap <silent> <cr> :call LanguageClient_textDocument_hover()<cr>

After opening a Reason project directory (dumb way: vim src/*.re) you may find that the first file is not properly highlighted: you may need to issue a :e command. Worse: if you open all the files together (vim -p src/*.re) you will have to repeat this for every buffer. Hit me up if you figure out what I’ve done wrong!

At this point, I recommend that you clone ‘reasonable fidelity’ so that you can follow along:

git clone git@github.com:Fusion/reasonable-fidelity.git

Of particular interest: src/jbuild – we are going to list all our libraries in this file to provide some helpful hints to editors and builder:

(jbuild_version 1)

(executable
 ((name main)
  (public_name reasonable-fidelity)
  (libraries (lwt cohttp cohttp-lwt-unix yojson str config-file extlib lymp diff curses))))

You can use the same list, almost verbatim, to manually install the required libraries:

opam install lwt cohttp cohttp-lwt-unix yojson str config-file extlib lymp diff curses

We are now ready to get to work…