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@).