hustodemon

(defn compute-next [[cur-pos cur-depth :as current] [dir quant :as instructions]]
  (case dir
    :forward [(+ cur-pos quant) cur-depth]
    :down    [cur-pos (+ cur-depth quant)]
    :up      [cur-pos (- cur-depth quant)]))

(defn compute-pos [[cur-pos cur-depth :as current] [[dir quant :as instructions] & rst]]
  [quant dir]
  (if (empty? instructions)
    (* cur-pos cur-depth)