Fully reactive UI in F# with observables

WinForm.fsx

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

type Action =
  | Increment
  | Decrement


let form = new Form(Width= 400, Height = 300, Visible = true, Text = "Hello World")
form.TopMost <- true

let panel = new FlowLayoutPanel()
panel.Dock <- DockStyle.Fill
panel.WrapContents <- false

let incBtn = new Button()
let decBtn = new Button()
let label = new Label()


incBtn.Text <- "+"
decBtn.Text <- "-"

incBtn.AutoSize <- true
decBtn.AutoSize <- true

panel.Controls.Add(incBtn)
panel.Controls.Add(label)
panel.Controls.Add(decBtn)

let model = 0

let view model =
  label.Text <- sprintf "%d" model


let update (model : int32) (action : Action) =
  match action with
    | Increment -> model + 1
    | Decrement -> model - 1


let increment = Control.Observable.map (fun _ -> Increment) incBtn.Click
let decrement = Control.Observable.map (fun _ -> Decrement) decBtn.Click

let actions = Control.Observable.merge increment decrement

let stateObservable = Control.Observable.scan update model actions

Control.Observable.subscribe view stateObservable

form.Controls.Add(panel)

form.Show()

This is inspired by Elm architecture.