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open System.IO
open System.ComponentModel
open System.Windows.Forms

let file = new StreamWriter("fibonacci.log", false)

file.WriteLine("Create the worker")
file.Flush()
let worker = new BackgroundWorker()
let numIterations = 1000

worker.DoWork.Add(fun args ->
    let rec computeFibonacci resPrevPrev resPrev i =
        // compute the next result
        let res = resPrevPrev + resPrev

        // At the end of the computation write the result into the mutable state
        if i = numIterations then
            file.WriteLine("end of computation")
            file.Flush()
            args.Result <- box res
        else
            // Compute the next result
            file.WriteLine(sprintf "PrevPrev:%i, Prev:%i, Next i:%i" resPrev res (i+1))
            file.Flush()
            computeFibonacci resPrev res (i+1)

    file.WriteLine(sprintf "PrevPrev:1, Prev:1, Next i:2")
    file.Flush()
    computeFibonacci 1 1 2)

worker.RunWorkerCompleted.Add(fun args ->
    file.WriteLine(sprintf "Result = %A" args.Result)
    file.Flush() |> ignore)

// Execute the worker
file.WriteLine("Execute the worker")
file.Flush()
worker.RunWorkerAsync()