(module loop_in_lambda_e2e

  (fn apply
    (doc "apply a fn-of-Int to an Int")
    (type (fn-type (params (fn-type (params (con Int)) (ret (con Int))) (con Int)) (ret (con Int))))
    (params f x)
    (body (app f x)))

  (fn main
    (doc "Iter it.1 — a loop inside a lambda body, invoked via a closure. The lambda computes x*x by summing x exactly x times through an accumulator loop; apply 7 prints 49. Codegen-soundness gate for the lambda-boundary loop_frames save/restore.")
    (type (fn-type (params) (ret (con Unit)) (effects IO)))
    (params)
    (body
      (app print
        (app apply
          (lam
            (params (typed x (con Int)))
            (ret (con Int))
            (body
              (loop ((var acc (con Int) 0) (var k (con Int) 0))
                (if (app == k x)
                  acc
                  (recur (app + acc x) (app + k 1))))))
          7)))))