(defn- ^File path-cat
  "Concatenate a path onto a file, with the same semantics as 'file."
  [f p]
  {:pre [f, p], :post [(cast File %)]}
  (let [f2 (io/file p)]
    (if (.isAbsolute f2) (io/file p) (io/file f p))))

(defn ^File file
  "Concatenate one or more paths. Absolute paths overrule all previous paths.
Concatenating a/b/c with /d/e/f results in /d/e/f."
  [path & more]
  {:pre [path], :post [(cast File %)]}
  (let [f (io/file path)]
    (if (empty? more) (io/file f) (reduce path-cat f more))))