https://twitter.com/gabegundacker/status/969323494092701697?s=21

coinstar.clj

(ns coinstar
  (:import [java.time LocalDate]))

(def working? (constantly false))

(defn go
  "Provided a `who` and `when`, returns the state of 
  a coinstar `when` the `who` goes to it.

  Example:
   (coinstar/go :i (LocalDate/now)) => false"
  [who when]
  {:pre [(and (= who :i)
              (instance? java.time.LocalDate when))]}
  (working?))