ctford

(ns shades.lenses)

; We only need three fns that know the structure of a lens.
(defn lens [focus fmap] {:focus focus :fmap fmap})
(defn view [x {:keys [focus]}] (focus x))
(defn update [x {:keys [fmap]} f] (fmap f x))

; The identity lens.
(defn fapply [f x] (f x))
(def id (lens identity fapply))