(module ownership_total

  (data List
    (doc "Monomorphic singly-linked Int list — boxed, recursive.")
    (ctor Nil)
    (ctor Cons (con Int) (con List)))

  (fn list_length
    (doc "Borrow the list, count its elements.")
    (type
      (fn-type
        (params (borrow (con List)))
        (ret (own (con Int)))))
    (params xs)
    (body
      (match xs
        (case (pat-ctor Nil) 0)
        (case (pat-ctor Cons h t)
          (app + 1 (app list_length t))))))

  (fn sum_list
    (doc "Consume the list, sum its elements.")
    (type
      (fn-type
        (params (own (con List)))
        (ret (own (con Int)))))
    (params xs)
    (body
      (match xs
        (case (pat-ctor Nil) 0)
        (case (pat-ctor Cons h t)
          (app + h (app sum_list t))))))

  (fn main
    (doc "Build [1,2,3]; print length (3) then sum (6).")
    (type (fn-type (params) (ret (own (con Unit))) (effects IO)))
    (params)
    (body
      (let xs
        (term-ctor List Cons 1
          (term-ctor List Cons 2
            (term-ctor List Cons 3
              (term-ctor List Nil))))
        (seq
          (seq (app print (app list_length xs)) (do io/print_str "\n"))
          (seq (app print (app sum_list xs)) (do io/print_str "\n")))))))