Playing around with Workflow Foundation in F#

I am also investigating Workflow Foundation. While workflow foundation is made a lot easier with appropriate GUI tool support, I still find it instructive to implement some examples in F# and see how it works. Here's a very simplistic workflow example impleted in F#:

#light 
#I @"C:\Program Files\Reference Assemblies\Microsoft\Framework\v3.0"
#r @"System.Workflow.Activities.dll"
#r @"System.Workflow.ComponentModel.dll"
#r @"System.Workflow.Runtime.dll"

open System
open System.Collections
open System.Threading
open System.Workflow.Activities
open System.Workflow.ComponentModel
open System.Workflow.Runtime
//
// Build a simple workflow 
//
type Workflow1 = class
   inherit SequentialWorkflowActivity as base

   val mutable createMessage : CodeActivity
   val mutable firstName : string
   val mutable message : string

   new() as this = {createMessage = null;firstName=null;message=null} then
      this.InitializeComponent()

   member this.FirstName with set value = this.firstName <- value
   
   member this.Message with get() = this.message
   
   (* Define workflow task *)
   member this.composeMessage sender (e:EventArgs) =
      this.message <- "Hello " + this.firstName + "!"

   (* Normally, Visual Studio would generate this with the help of GUI tools *)
   member this.InitializeComponent () =
      this.CanModifyActivities <- true
      this.createMessage <- new System.Workflow.Activities.CodeActivity()

      // create Message
      this.createMessage.Name <- "createMessage"
      this.createMessage.ExecuteCode.AddHandler
         (new System.EventHandler(this.composeMessage))


      // Workflow1
      this.Activities.Add(this.createMessage)
      this.Name <- "Workflow1"
      this.CanModifyActivities <- false

end
//
// Workflow Engine Hosting Code
//
let main =

   using (new WorkflowRuntime()) (fun wfRuntime ->
      let waitHandle = new AutoResetEvent(false)
   
      wfRuntime.WorkflowCompleted.Add
         (fun (e:WorkflowCompletedEventArgs) -> 
            let message = e.OutputParameters.["Message"]
            Console.WriteLine(message)
            waitHandle.Set() |> ignore)
      
      wfRuntime.WorkflowTerminated.Add
        (fun (e:WorkflowTerminatedEventArgs) ->
           Console.WriteLine(e.Exception.Message)
           waitHandle.Set()|>ignore)
        
      let inparam = new Generic.Dictionary<string, obj>()
      inparam.Add("FirstName",box("Joe"))
     
      let instance = wfRuntime.CreateWorkflow(typeof<Workflow1>,inparam)
      instance.Start() |> ignore
      waitHandle.WaitOne() |> ignore
      Console.WriteLine("Done!")
   )

// Execute the workflow   
do main