;;;; spec-memory.md, "Dev builds detect a released region" — the Map's half.
;;;;
;;;; A Map records the epoch of the allocator it was made with, exactly as a
;;;; Vec does, and free-all bumps that counter. Any operation on a container
;;;; whose recorded epoch has moved traps, naming the site.
;;;;
;;;; This is worth its own program rather than a line in stale-region.flan
;;;; because the two containers reach the check by different routes: a Vec's
;;;; every operation takes the Vec's address and checks on the way in, while a
;;;; map's get goes on to call a hash and an equality function through pointers
;;;; into a block that is no longer there. If the check were missing here, the
;;;; failure would not be a wrong number — it would be a probe loop walking
;;;; released memory.
(defn main [] i32
  (let [a (arena-new 65536)]
    (let [m (map-new i32 i32 a)]
      (put m 1 10)
      (put m 2 20)
      (match (get m 2) (Some v) (println v) None (println "missing"))
      ;; The region goes. m is still in scope and still looks fine — nothing is
      ;; released at scope exit and nothing marked m — which is exactly the
      ;; case a static rule cannot see.
      (free-all a)
      (match (get m 2) (Some v) (println v) None (println "missing"))))
  0)