When using settable-fn.arc:

  (def create-my-type ()
    (add-attachments
      'key (fn () (generate-keys))
               ; note the order: value before key(s)
      '=   (fn (v k)  (assign-value-v-to-key-k v k))
      (annotate 'my-type
        (fn (k)
          (lookup-in-k k)))))

  (def create-my-type ()
    (add-attachments
      'key (fn () (generate-keys))
      '=   (fn (v k)  (assign-value-v-to-key-k v k))
      'type 'my-type
      (fn (k)
        (lookup-in-k k))))