;; A closure's environment is found by walking the storage its function value
;; sits in — a frame slot, a global, a struct, an Option, a Vec's elements —
;; and a Map's storage is not walked. An (Fn ...) as a Map's value would hold
;; an environment the collector cannot see and would free. A Vec holds them,
;; and a (CFn ...) carries no environment and may go in a Map.
(defn main [] i32
  (let [ops (map-new string (Fn [i32] i32))]
    (put ops "id" (fn [x] x))
    0))