type IO<'a> = private IO of (unit -> 'a)

type IOBuilder () =
    member inline this.Bind (IO x : IO<'a>, f: 'a -> IO<'b>) : IO<'b> =
        f (x ())

    member inline this.Bind (x: IO<'a> list, f: 'a list -> IO<'b>) : IO<'b> =
        f (x |> List.map (fun (IO x) -> x ()))

    member inline this.Delay (f: unit -> IO<'a>) : IO<'a> =
        IO (fun _ -> match f () with | IO x -> x ())

    member inline this.Return (x: 'a) : IO<'a> =
        IO (fun _ -> x)

    member inline this.ReturnFrom (IO x : IO<'a>) : IO<'a> =
        IO (fun _ -> x ())

let io = IOBuilder ()

[<RequireQualifiedAccess>]
module IO =
    let inline run (IO x) = x ()