;; A dyn is the one thing a capture refuses outright, and for the reason a
;; struct field of dyn already refuses: the collector's roots are frames, and
;; nothing pushes the fields of the environment struct a capture synthesises.
;; A copy in there would be a live value reachable only through memory the
;; marker never walks. Milestone 2's per-type descriptors lift it, alongside
;; the condition payload's and the struct field's.
(defn run [f (Fn [] i64)] i64 (f))

;; [d] is unannotated, which is what makes it a dyn.
(defn use [d] i64
  (run (fn [] (i64 d))))

(defn main [] i32 (println (use 7)) 0)