ghc-mod

Namely, you want the ghc-mod plugin since it provides the hooks into the compiler to query type information.

With ghc-mod and vim/emacs configured, you'll be notified upon saving if you blew up something in the current file.

This also affected other things that used a GHCi-like code path like Template Haskell and the GHC APIs used by ghc-mod/hdevtools.

That ghc-mod happens to be a command-line application is utterly irrelevant to the end-user unless they want to go poking around.

Haskell has some alternatives like ghc-mod[9] and scion[10], but I've never been able to get them to work.

I recently installed ghc-mod [1] and configured it in Emacs; red squiggly lines appear when I have an error.

What I get from that is my code is checked for style/compile errors everytime I save with ghc-mod and hlint.

Note that you need ghc-mod installed for syntastic to take effect though.

Libraries like haskell-suite and command-line tooling like ghc-mod have succeeded in that.

I think the existence of ghc-mod for incremental compiling and the interpreter repl really don't make compile times a big deal.

You'll note that it's not actually a command-line app like ghc-mod.

When I wrote it, ghc-mod and scion only supported show-type-at-point when the file typechecks, which is more or less useless when refactoring.

I use ghc-mod because it's "simple" and easily inspectable/dumpable for it's output at the terminal.

Nix is great but you have to take some time to set it up and learn it - sandboxes are pretty standard and work as you would expect with ghc-mod (not that Nix doesn't I just had more time invested in getting it and the tooling setup to use it as a "dev environment" - cabal sandboxes are much simpler).