如何在F#中使用winforms制作模拟时钟？

open System
open System.Windows.Forms
open System.Drawing

type ClockForm() as this =
    inherit Form(Text = "模拟时钟", Width = 300, Height = 300)

    let timer = new Timer(Interval = 1000)
    let mutable currentTime = DateTime.Now

    do
        timer.Tick.Add(fun _ ->
            currentTime <- DateTime.Now
            this.Invalidate())

    override this.OnPaint(e: PaintEventArgs) =
        let g = e.Graphics
        let center = new Point(this.Width / 2, this.Height / 2)
        let radius = Math.Min(this.Width, this.Height) / 2 - 10

        g.SmoothingMode <- Drawing2D.SmoothingMode.AntiAlias

        // 绘制表盘
        g.DrawEllipse(Pens.Black, center.X - radius, center.Y - radius, radius * 2, radius * 2)

        // 绘制时针
        let hourAngle = (float currentTime.Hour + float currentTime.Minute / 60.0) * 30.0
        let hourLength = radius * 0.5
        let hourEnd = new Point(int(float center.X + sin(hourAngle * Math.PI / 180.0) * hourLength),
                                int(float center.Y - cos(hourAngle * Math.PI / 180.0) * hourLength))
        g.DrawLine(Pens.Black, center, hourEnd)

        // 绘制分针
        let minuteAngle = float currentTime.Minute * 6.0
        let minuteLength = radius * 0.7
        let minuteEnd = new Point(int(float center.X + sin(minuteAngle * Math.PI / 180.0) * minuteLength),
                                  int(float center.Y - cos(minuteAngle * Math.PI / 180.0) * minuteLength))
        g.DrawLine(Pens.Black, center, minuteEnd)

        // 绘制秒针
        let secondAngle = float currentTime.Second * 6.0
        let secondLength = radius * 0.9
        let secondEnd = new Point(int(float center.X + sin(secondAngle * Math.PI / 180.0) * secondLength),
                                  int(float center.Y - cos(secondAngle * Math.PI / 180.0) * secondLength))
        g.DrawLine(Pens.Red, center, secondEnd)

    static member Main() =
        Application.Run(new ClockForm())