open! Import

type t = (int, string) Either.t [@@deriving sexp_of]

let f : t = First 0
let s : t = Second "str"

let%expect_test "First.Monad.map" =
  let open Either.First.Let_syntax in
  let inc x =
    let%map v = x in
    v + 1
  in
  let f' = inc f in
  let s' = inc s in
  print_s [%message (f' : t) (s' : t)];
  [%expect {|
    ((f' (First  1))
     (s' (Second str)))
    |}]
;;

let%expect_test "Second.Monad.map" =
  let open Either.Second.Let_syntax in
  let add x =
    let%map v = x in
    String.concat [ v; "1" ]
  in
  let f' = add f in
  let s' = add s in
  print_s [%message (f' : t) (s' : t)];
  [%expect {|
    ((f' (First  0))
     (s' (Second str1)))
    |}]
;;

let%expect_test "First.Monad.bind" =
  let open Either.First.Let_syntax in
  let inc x =
    let%bind v = x in
    return (v + 1)
  in
  let f' = inc f in
  let s' = inc s in
  print_s [%message (f' : t) (s' : t)];
  [%expect {|
    ((f' (First  1))
     (s' (Second str)))
    |}]
;;

let%expect_test "Second.Monad.bind" =
  let open Either.Second.Let_syntax in
  let add x =
    let%bind v = x in
    return (String.concat [ v; "1" ])
  in
  let f' = add f in
  let s' = add s in
  print_s [%message (f' : t) (s' : t)];
  [%expect {|
    ((f' (First  0))
     (s' (Second str1)))
    |}]
;;

let%expect_test "First.map2" =
  let m t1 t2 =
    let result = Either.First.map2 ~f:(fun x y -> x + y) t1 t2 in
    print_s [%sexp (result : (int, string) Either.t)]
  in
  let foo = "foo" in
  let bar = "bar" in
  m (Second foo) (Second bar);
  [%expect {| (Second foo) |}];
  m (First 1) (First 2);
  [%expect {| (First 3) |}];
  m (Second foo) (First 1);
  [%expect {| (Second foo) |}];
  m (First 1) (Second bar);
  [%expect {| (Second bar) |}]
;;

let%expect_test "Second.map2" =
  let m t1 t2 =
    let result = Either.Second.map2 ~f:(fun x y -> x + y) t1 t2 in
    print_s [%sexp (result : (string, int) Either.t)]
  in
  let foo = "foo" in
  let bar = "bar" in
  m (First foo) (First bar);
  [%expect {| (First foo) |}];
  m (Second 1) (Second 2);
  [%expect {| (Second 3) |}];
  m (First foo) (Second 1);
  [%expect {| (First foo) |}];
  m (Second 1) (First bar);
  [%expect {| (First bar) |}]
;;