TestBuilder.fs

type NonEmptyList<'T> = 'T * 'T list

type AssertResult<'T> =
  | Failure of NonEmptyList<string>
  | Success of 'T

type TestBuilder(description: string) =
// これを解除するとコンパイルエラーになってしまう・・・
//  member __.Bind(x, f) =
//    match x with
//    | Success res -> f res
//    | Failure res -> Failure res

  member __.Bind(x, f) =
    match x with
    | Success () -> f ()
    | Failure (res1, rest1) ->
        match f () with
        | Success _ -> Failure (res1, rest1)
        | Failure (res2, rest2) ->
            Failure (res1, rest1@(res2::rest2))

  member __.Return x = Success x
  member __.Zero () = Success ()

let assertEquals x y =
  if x = y then Success ()
  else Failure (sprintf "Expect: %A\nActual: %A" x y, [])

let test description = TestBuilder(description)

test "hogehoge" {
  do! assertEquals 1 2
  do! assertEquals 2 3
  do! assertEquals 2 2
  do! assertEquals 3 4
}
(* => val it : AssertResult<unit> =
  Failure
    ("Expect: 1
Actual: 2", ["Expect: 2
Actual: 3"; "Expect: 3
Actual: 4"]) *)

BindじゃなくてCombineに頼る方向性のほうがやっぱりいいのかも？