(module loop_nested_in_lambda

  (fn make_adder
    (doc "Iter it.1 — a loop inside a lambda body (lambda-boundary analogue). Iter it.2: the returned closure is loop-bearing, so its arrow carries !Diverge (DD-4 lam boundary); make_adder's return type reflects that. make_adder's own body does not contain the loop (it stops at the lam edge), so make_adder itself stays effect-free.")
    (type (fn-type (params (con Int)) (ret (fn-type (params (con Int)) (ret (con Int)) (effects Diverge)))))
    (params base)
    (body
      (lam
        (params (typed x (con Int)))
        (ret (con Int))
        (effects Diverge)
        (body
          (loop ((var acc (con Int) base) (var k (con Int) 0))
            (if (app == k x)
              acc
              (recur (app + acc 1) (app + k 1)))))))))