#time "on"
type MyRecType() =

  let list = System.Collections.Generic.List()

  member this.DoWork() =
    let mutable tcs = (System.Runtime.CompilerServices.AsyncTaskMethodBuilder<int>.Create())
    let returnTask = tcs.Task // NB! must access this property first
    let mutable local = 1

    let rec outerLoop() =
      if local < 1000000 then
        innerLoop(1)
      else
        tcs.SetResult(local)
        ()

    and innerLoop(inc:int) =
      if local % 2 = 0 then
        local <- local + inc
        outerLoop()
      else
        list.Add(local) // just fake access to a field to illustrate the pattern
        local <- local + 1
        innerLoop(inc)

    outerLoop()

    returnTask


let instance = MyRecType()

instance.DoWork().Result

> Real: 00:00:00.019, CPU: 00:00:00.031, GC gen0: 0, gen1: 0, gen2: 0
> val it : int = 1000001

member this.DoWork2() =
    let mutable tcs = (System.Runtime.CompilerServices.AsyncTaskMethodBuilder<int>.Create())
    let returnTask = tcs.Task // NB! must access this property first
    let mutable local = 1
    let rec loop(isOuter:bool, inc:int) =
      if isOuter then
        if local < 1000000 then
          loop(false,1)
        else
          tcs.SetResult(local)
          ()
      else
        if local % 2 = 0 then
          local <- local + inc
          loop(true,1)
        else
          list.Add(local) // just fake access to a field to illustrate the pattern
          local <- local + 1
          loop(false,1)

    loop(true,1)

    returnTask


> Real: 00:00:00.004, CPU: 00:00:00.015, GC gen0: 0, gen1: 0, gen2: 0
> val it : int = 1000001