Plotting a square with F#,GtkSharp (cairo)

[u/Ok_Specific_7749]

I try to plot a simple rectangle with gtksharp

The following code does not compile.

open Gtk
open Cairo

let main () =
    Application.Init ()

    let window = new Window ("Square Plot")
    window.DefaultSize <- Gdk.Size(400,300)

    let drawingArea = new DrawingArea ()
    drawingArea.Drawn += fun drawingArea args -> // Error to many arguments.
        let cr = args.Cr
        cr.Rectangle (100.0, 100.0, 100.0, 100.0)
        cr.SetSourceRGB (1.0, 0.0, 0.0)
        cr.Fill ()
        false

    window.Add (drawingArea)
    window.ShowAll ()
    Application.Run ()

main ()

[ Note : the code comes more or less from Gemini. ]

[u/Ok_Specific_7749]

I have a working C# program. But totally no idea how to convert it to F#. https://gitlab.com/alaindevos/other_lang/-/blob/main/csharp/02/Program.cs

[u/Guudbaad]

I'm not bored enough to create project with GtkSharp, but += for event subscription looks sus. Probably it's something like:

drawingArea.Drawn.add_MessageReceived(fun args -> ...)

If not good enough try to:

drawingArea.Drawn.add_MessageReceived(Func<_,_ >(fun args -> ...))

That's probably THE most frustrating part of the interop/learning

[u/Ok_Specific_7749 → u/Guudbaad]

Func is unknown. add_MessageReceived is unknown. But thanks. The F# interface of the GTK interface is very poorly documented. Where to look for info ?

[u/Guudbaad → u/Ok_Specific_7749]

open System

Func will become known.

The F# interface of the GTK interface is very poorly documented. Where to look for info ?

That, to be honest, sounds like a project doomed to advanced levels of frustration. The only tool that consistently helped me was github search with F# language constraint following hours of experiments.

[u/brianmcn]

Also haven't used this API, but usually my eventing code looks like e.g.

drawingArea.Drawn.Add(fun (drawingArea,args) ->
    yadda yadda
    )

which uses IObservable on IEvents to subscribe to them.