How I would prefer to write https://stackoverflow.com/a/54494511/2314532

gistfile1.txt

let RunProcess (startInfo : ProcessStartInfo) =
    let bufferOutput = new StringBuilder()
    let bufferError  = new StringBuilder()
    let dataHandler handler = DataReceivedEventHandler(fun sender args -> try handler args.Data with _ -> ())
    let append  (sb: StringBuilder) txt = sb.Append(txt + "\n") |> ignore
    let consume (sb: StringBuilder)     = sb.ToString() |>! (fun _ -> sb.Clear() |> ignore)
    let outputHandler = append bufferOutput |> dataHandler
    let errorHandler  = append bufferError  |> dataHandler
    startInfo.RedirectStandardInput  <- true
    startInfo.RedirectStandardOutput <- true
    startInfo.RedirectStandardError  <- true
    startInfo.UseShellExecute <- false
    let proc = new Process(StartInfo           = startInfo,
                           EnableRaisingEvents = true)
    outputHandler |> proc.OutputDataReceived.AddHandler
    errorHandler  |> proc.ErrorDataReceived .AddHandler
    let r = proc.Start() 
    proc.BeginOutputReadLine()
    proc.BeginErrorReadLine()
    proc.WaitForExit()
    let output = (consume bufferOutput).Trim()
    let error  = (consume bufferError ).Trim()
    ((if proc.HasExited then proc.ExitCode else -99999), output, error)