Hi all, I have just uploaded ghc-mod v3.0.0 to Hackage. In this version, ghc-mod supports the sandbox feature of "cabal-install". Instead, it stopped supporting "cabal-dev". If you want to use ghc-mod v3.0.0, I would recommand to install cabal-install 1.18. The sandbox in your package is automatically detected by ghc-mod if exists. --Kazu