To delete a directory recursively in Clojure.

delete-recursively.clj

(defn delete-recursively [fname]
  (let [func (fn [func f]
               (when (.isDirectory f)
                 (doseq [f2 (.listFiles f)]
                   (func func f2)))
               (clojure.java.io/delete-file f))]
    (func func (clojure.java.io/file fname))))

Just for fun, here's one that is tail recursive. The fs arg will act as the stack instead of the thread stack, growing as it traverses the file structure in a depth-first post-order search:

(defn tail-recursive-delete
  [& fs]
  (when-let [f (first fs)]
    (if-let [cs (seq (.listFiles (io/file f)))]
      (recur (concat cs fs))
      (do (io/delete-file f)
          (recur (rest fs))))))