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I'm surprised no one has mentioned geiser. It sounds like exactly what you want for racket. http://nongnu.org/geiser/geiser_3.html

There is also racket-mode (available on MELPA): https://github.com/greghendershott/racket-mode

This is what I use. I find it quite comfortable / very easy to get going.

Geiser is fine. However, we can’t compare it with SLIME. The integration of the latter is much better.