You should use Emacs to edit Racket code; Dr. Racket, which ships with
Racket, is a bit too limited an editor for the number of files and
complexity of Herbie. You’ll want to use the quack and geiser Emacs
packages to give you Racket-specific highlighting and a Racket REPL.
The easiest way to install these is to run
(require 'package)
(add-to-list 'package-archives
'("marmalade" . "http://marmalade-repo.org/packages/"))
(package-initialize)
(mapcar #'package-install '(quack geiser))
This needs to be done once. You can now open a Racket file, like
herbie/main.rkt, and the mode-line will read Scheme Racket/A,
indicating that Quack, the Scheme mode, is running.
If you hit C-c C-a in a Racket buffer, you’ll open up a REPL and
“enter” that module, allowing you to refer to definitions in it. The
same C-c C-a binding reloads the file, while C-M-x reloads
individual definitions and C-c C-e executes individual
S-expressions.