open! Import
open! Lazy

let%test_unit _ =
  let r = ref 0 in
  let t =
    return ()
    >>= fun () ->
    Int.incr r;
    return ()
  in
  assert (!r = 0);
  force t;
  assert (!r = 1);
  force t;
  assert (!r = 1)
;;

let%test_unit _ =
  let r = ref 0 in
  let t = return () >>= fun () -> lazy (Int.incr r) in
  assert (!r = 0);
  force t;
  assert (!r = 1);
  force t;
  assert (!r = 1)
;;

let%expect_test "peek" =
  let t =
    lazy
      (print_endline "force t";
       "forced")
  in
  print_s [%sexp (peek t : string option)];
  [%expect {| () |}];
  ignore (force t : string);
  [%expect {| force t |}];
  print_s [%sexp (peek t : string option)];
  [%expect {| (forced) |}]
;;

let%test_module _ =
  (module struct
    module M1 = struct
      type nonrec t = { x : int t } [@@deriving sexp_of]
    end

    module M2 = struct
      type t = { x : int T_unforcing.t } [@@deriving sexp_of]
    end

    let%test_unit _ =
      let v = lazy 42 in
      let (_ : int) =
        (* no needed, but the purpose of this test is not to test this compiler
           optimization *)
        force v
      in
      assert (is_val v);
      let t1 = { M1.x = v } in
      let t2 = { M2.x = v } in
      assert (Sexp.equal (M1.sexp_of_t t1) (M2.sexp_of_t t2))
    ;;

    let%test_unit _ =
      let t1 = { M1.x = lazy (40 + 2) } in
      let t2 = { M2.x = lazy (40 + 2) } in
      assert (not (Sexp.equal (M1.sexp_of_t t1) (M2.sexp_of_t t2)));
      assert (is_val t1.x);
      assert (not (is_val t2.x))
    ;;
  end)
;;

let%expect_test "equal" =
  let lazy_a =
    lazy
      (print_endline "force lazy_a";
       1)
  in
  let lazy_b =
    lazy
      (print_endline "force lazy_b";
       1)
  in
  let lazy_c =
    lazy
      (print_endline "force lazy_c";
       2)
  in
  (* [phys_equal] short-circuiting without [force] *)
  print_s [%sexp (equal Int.equal lazy_a lazy_a : bool)];
  [%expect {| true |}];
  (* [force], resulting in [true] *)
  print_s [%sexp (equal Int.equal lazy_a lazy_b : bool)];
  [%expect {|
    force lazy_b
    force lazy_a
    true
    |}];
  (* [force], resulting in [false] *)
  print_s [%sexp (equal Int.equal lazy_b lazy_c : bool)];
  [%expect {|
    force lazy_c
    false
    |}]
;;
