This package is only useful in combination with a language server for Haskell. The only implementation so far (Nov '18) is the haskell-ide-engine (hie): https://github.com/haskell/haskell-ide-engine Its packaging is blocked on having it uploaded to hackage first: https://github.com/haskell/haskell-ide-engine/issues/626 Thus you need to git clone hie and build it yourself. To troubleshoot problems inspect the buffer *lsp-haskell stderr*. -- Thomas Koch , Tue, 27 Nov 2018 18:38:07 +0000