F# fibonacci in tail recursion with memoize

memofib2.fsx

let memoize fn =
  let cache = new System.Collections.Generic.Dictionary<_,_>()
  printfn "counter: %A" cache.Count
  
  fun x ->
    printfn "%A is received" x
    match cache.TryGetValue x with
    | true, v -> v
    | false, _ -> let v = fn (x)
                  cache.Add(x,v)
                  v

let fib n =
  let rec loop acc1 acc2 n =
    match n with
    | 0 -> acc1
    | 1 -> acc2
    | _ -> loop acc2 (acc1 + acc2) (n - 1)
    
  loop 0 1 n

let memo_fib = memoize fib

let sw = new System.Diagnostics.Stopwatch()
sw.Start()
memo_fib 45 |> printfn "%A"
sw.ToString() |> printfn "%s"