(module fp_map
  (data IntList
    (doc "boxed list")
    (ctor Nil)
    (ctor Cons (con Int) (con IntList)))
  (fn map_int
    (doc "recursive HOF: f applied AND passed to the recursive call")
    (type (fn-type
            (params (borrow (fn-type (params (own (con Int))) (ret (own (con Int))))) (own (con IntList)))
            (ret (own (con IntList)))))
    (params f xs)
    (body (match xs
      (case (pat-ctor Nil) (term-ctor IntList Nil))
      (case (pat-ctor Cons h t) (term-ctor IntList Cons (app f h) (app map_int f t)))))))