Setting Up Merlin in Neovim

My OCaml development environment in Debian has been working well since I set it up.   In this post I talk about setting up Merlin in vim and neovim.  See this discussion for other well-liked OCaml environment set up.   I’ve been using neovim and I like it so I’ll stick with this for now.

Setting Up Merlin in Vim

First, Merlin has to be installed.  Installing Merlin using OPAM was smooth and easy.  I just ran

opam install merlin

and it worked.  Then, because I want to use it in vim, I need to put the following in vimrc to add Merlin to the runtime path (see this guide):

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

Run :so .vimrc in your home directory (or wherever your vimrc is) in vim to make vim see the .vimrc changes.  After this, Merlin works in vim!  I can call Merlin commands like :MerlinErrorCheck in vim!

Setting Up Merlin in Neovim

However, it only works in plain vim but not neovim.  I prefer neovim to vim because, among other reasons, it has a cleaner code base than vim.  To get Merlin working in neovim, I need the python-neovim and python3-neovim packages.  The problem is, neither of the python packages are in Debian Stretch (stable), the version of Debian I’m in.  However, they are in Debian Buster (testing).

So I proceed by following this link.  I temporarily told my Debian to grab software from the testing version source list:

1.  Edit the “etc/apt/sources.list” file, changing the source from stable to testing.
2.  Run apt update to get the new source list.
3.  Grab the python-neovim and python3-neovim packages using apt.  (Run apt install python-neovim python3-neovim)
4.  Revert the “etc/apt/sources.list” file, changing the source from testing back to stable.
5.  Run apt update again to get the source list from stable again.

The next thing I know, I couldn’t log back into my computer after I came back from lunch!  Apparently I uninstalled my display manager and window manager in the above process!  What happened was that when I installed the python packages, apt, working on the assumption that I was on testing, noticed some packages were no longer needed.  I ran apt autoremove to remove them, and removed packages that I needed!  I should have been more careful about removing packages.

Anyway, I’m now on Debian Buster, with Merlin working in my neovim!  I hope the testing version of Debian is not too unstable for me.  I’ll let you know!