NecoGhc combined with Deoplete are a way better solution to get code completion running for neovim. Please give it a try!
This plugin offers GhcMod support for Neovim. It's still in a very early stage.
GhcModCaseSplit: split the pattern variable under the cursor (saves current file)GhcModAddDecl: inserting function declaration based on type signature under the cursor (saves current file)GhcModRefine: prompts for an expression and refines the hole under the cursor (saves current file)
This feature requires ghc-modi.
You can configure an explicit path to your ghc-modi binary if needed by setting g:ghc_modi_executable.