Question

I have a type

type figure =
{
   what : int;
   position : Point;
   size : Point;
}

and i want my function to return this type, however since it’s an event it wants to return a unit ()
how can i get my function to return this type instead of unit?

let checkInput = 
drawArea.MouseClick.Add(fun args -> 
    if args.Button = MouseButtons.Left then 
        new figure { what = 0; position = new Point(args.X, args.Y); size = new Point(50, 50) })

any help on this would be appreciated

Answer 1

In your example the compiler doesn’t know what to do with the new figure you created. Figure needs to be stored somewhere or passed to a function. Here’s an example where it’s passed to a function. When you click in the form the title is updated to the clicked position.

open System.Drawing
open System.Windows.Forms

type Figure = {
   what : int;
   position : Point;
   size : Point;
}

let drawArea = new Form()

let print figure =
    drawArea.Text <- figure.position.ToString()

drawArea.MouseClick.Add(fun args -> 
    if args.Button = MouseButtons.Left then 
        print { what = 0; position = Point(args.X, args.Y); size = Point(50) }
)

Application.Run(drawArea)

You will need to include these two assemblies under references in your project for this example.

System.Drawing
System.Windows.Forms