(module real_consume
  (data Box
    (doc "heap cell")
    (ctor Box (con Int)))
  (data Pair
    (doc "two boxes")
    (ctor Pair (con Box) (con Box)))
  (fn dup
    (doc "MUST STAY an error: a heap param consumed twice without clone")
    (type (fn-type (params (own (con Box))) (ret (own (con Pair)))))
    (params b)
    (body (term-ctor Pair Pair b b))))