(defstruct AssetMissing [id i32])

(defvar seen i64)

(defn load-all []
  (signal (AssetMissing {:id 1}))     ; Unit — the caller carries on
  (signal (AssetMissing {:id 2})))

(defn main []
  (load-all)                          ; no handler: a no-op
  (print seen) (println "")           ; 0

  ;; A handler that returns normally accumulates and lets the signaller run on.
  (handler-bind [(AssetMissing [c] (set seen (+ seen (i64 (.id c)))))]
    (load-all))
  (print seen) (println ""))          ; 3