As of May, 25th 2022, this project is officially unmaintained. If you would like to take over, drop a message to @lierdakil.
If you're looking for a decent editor support for Haskell, consider using VSCode with Haskell extensions.
Autocomplete-haskell provides autocompletion facilities for your Haskell
hacking.
It relies on scope names provided by language-haskell and haskell-completion-backend service, provided by haskell-ghc-mod
You can show auto-completions for hole _. This will try to find replacements
based on type. It’s no magic though, so if hole has some crazy type, it won’t
find anything. You can also refine hole completions based on name by using named holes, e.g. _from
Sadly, it does not pick up types and/or other symbols defined in current file (ghc-mod seems to be incapable of this feat), so for this you have to rely on default autocomplete-plus SymbolProvider.