let each xs callback = List.map callback xs

let () =
  assert ((let%continue x = each [1; 2; 3] in x * 5) = [5; 10; 15]);
  assert ((let%cps x = each [1; 2] in x + 1) = [2; 3]);
  assert ((let%continue (x, y) = each [2, 3] in x + y) = [5]);
  assert ((let%continue x = each [1; 2] in
           let%continue y = each [3; 4] in x + y) = [[4; 5]; [5; 6]]);
  let active = ref false in
  let scope callback = active := true; callback (); active := false in
  (let%continue () = scope in assert !active);
  assert (not !active);
  let calls = ref 0 in
  let producer () = incr calls; each [1; 2] in
  assert ((let%continue x = producer () in x) = [1; 2]);
  assert (!calls = 1);
  assert ((let%continue _ = each [] in failwith "unreachable") = []);
  assert ((let%continue x = (let%continue f = each [each [7]] in f) |> List.hd
           in x + 1) = [8]);
  (try (let%continue () = scope in failwith "callback"); assert false
   with Failure message -> assert (message = "callback"));
  print_endline "continuum_ppx: behavior checks passed"