I tried using ale with mix only but couldn’t get it working. I also couldn’t see where to start to make it work with elixir-ls. Then I found vim-elixirls which helps integrating ale with elixir-ls. It even provides a Vim command to download and compile elixir-ls. From my initial testing it seems to work very well. I like that it’s compatible with the original Vim and doesn’t require to install Node.js.
Thank you all for sharing your knowledge and letting me embrace the power of LSP 
