Either "GHCi as a daemon" or "GHC + a bit of an IDE". A very simple Haskell development tool which shows you the errors in your project and updates them whenever you save. Run ghcid --topmost --command=ghci, where --topmost makes the window on top of all others (Windows only) and --command is the command to start GHCi on your project (defaults to ghci if you have a .ghci file, or else to cabal repl).