;; Coercion between the two function types goes one way only. A (CFn ...)
;; widens into a (Fn ...) through a per-signature thunk, and a (Fn ...) does
;; not narrow: there is nowhere for the environment to go, and nothing at this
;; definition can know whether there is one.
;;
;; Refused by the ordinary type message, which names both spellings and is the
;; right sentence for it: the fix is to widen the position, not to convert the
;; value.
(defn apply-bare [f (CFn [i32] i32)  x i32] i32 (f x))

(defn hand-on [f (Fn [i32] i32)  x i32] i32 (apply-bare f x))

(defn main [] i32 0)