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Documenting everything about OCaml


Editor Setup

Merlin is the tool used for code completion, type querying, locating definitions etc for OCaml. Regardless of which editor you use, you’ll want to install Merlin for your ocaml compiler with opam install merlin.

Visual Studio Code

This is the easiest editor to set up for OCaml. Just install the OCaml Platform extension (see README for instructions).

Vim or Neovim

Vim and neovim are relatively complex tools, and their configuration requires editing their .vimrc file (in the case of Neovim, it’s .config/nvim/init.vim on Linux). If you use neovim, you can either use Merlin, which is OCaml’s main code-information tool, or ocaml-lsp, which is a language server protocol wrapper on top of Merlin.

Merlin Plugin

In order to just have basic Merlin support, all you need is to add this snippet to enable Merlin’s VIM plugin:

if executable('opam')
  let g:opamshare=substitute(system('opam var share'),'\n$','','''')
  if isdirectory(g:opamshare."/merlin/vim")
    execute "set rtp+=" . g:opamshare."/merlin/vim"

This approach has the advantage of loading the same plugin version as is available in Merlin via OPAM, preventing any mismatches.

Use :help merlin to find out the keybindings. A completion engine, like Ale, is recommended as well.


Neovim supports LSP servers natively. To add LSP support to Vim, you’ll need an extra addon. To run Neovim with LSP support, the easiest way is to install nvim-lspconfig and configure the necessary lines for ocaml-lsp support. Make sure to install ocaml-lsp via opam and you’re done.


Install tooling libraries and the user-setup assitant with

opam install user-setup merlin tuareg ocamlformat ocp-indent

Then run the user-setup installation

opam user-setup install