F# fibonacci module

fibonacci.fsx

module fibonacci

open System.Collections.Generic

let rec fib n =
  match n with
  | 0 | 1 -> n
  | n -> fib (n-1) + fib (n-2)

[<TailCall>]
let fib_memo n =
  let memo = new Dictionary<_,_>()

  let rec fib n = 
    let isExist, value = memo.TryGetValue n

    if isExist then
      //printf "!"
      value
    else
      match n with
      | 0 | 1 -> n
      | n ->
        let value = fib (n-1) + fib (n-2)
        memo.Add(n, value)
        value
  
  fib n

[<TailCall>]
let fib_tail_recursion n =
  let rec loop acc1 acc2 n =
    match n with
    | 0 -> acc1
    | 1 -> acc2
    | _ -> loop acc2 (acc1 + acc2) (n - 1)
    
  loop 0 1 n