I’d like to second racket-mode with Emacs. If you want a ton of IDE-like smarts, fire up racket-xp-mode (racket eXPlore mode, comes bundled with racket-mode). Pairs nicely with other good things in the Emacs ecosystem.
Just a note in case someone goes looking for racket-xp-mode explicitly. It's just an ancillary mode included with racket-mode. You'll pretty much always want it turned on. I'm sure there's some reason to turn it off sometime, but I've never done it.
