Your example isn't a very functional code style though so I don't know that I'd consider it to be idiomatic. Generally code written in a functional style ends up indented many layers deep. Below is a quick (and quite tame) example from one of the introductory guides for Racket. My code often ends up much deeper. Consider what it would look like if one of the cond branches contained a nested cond.

  (define (start request)
    (define a-blog
      (cond [(can-parse-post? (request-bindings request))
             (cons (parse-post (request-bindings request))
                   BLOG)]
            [else
             BLOG]))
    (render-blog-page a-blog request))

https://docs.racket-lang.org/continue/index.html