Here’s how to get started with vim and ReasonML.

Start by installing bs-platofrm.

npm install -g bs-platform

For syntax highlighting, install vim-reason-plus.

Plugin 'reasonml-editor/vim-reason-plus'

For type hints and autocompletion, you can use vim-lsp.

Plugin 'prabirshrestha/async.vim'
Plugin 'prabirshrestha/vim-lsp'
Plugin 'prabirshrestha/asyncomplete.vim'
Plugin 'prabirshrestha/asyncomplete-lsp.vim'

Next, install the ocaml-language-server. This requires Merlin, which you can install using another set of tools, reason-cli.

npm install -g reason-cli@latest-linux
npm install -g ocaml-language-server

Lastly, add the following to your .vimrc.

if executable('ocaml-language-server')
    au User lsp_setup call lsp#register_server({
      \ 'name': 'ocaml-language-server',
      \ 'cmd': {server_info->[&shell, &shellcmdflag, 'ocaml-language-server --stdio']},
      \ 'whitelist': ['reason', 'ocaml'],
      \ })
endif