Fibonacci server with Dream

fibonacci.ml

let state : (int * int) list ref = ref []

let rec fibonacci (n : int) : int =
  if n <= 1 then 1
  else
    match List.assoc_opt n !state with
    | Some v -> begin
      print_string "Cache hit :)"; 
      print_newline ();
      v
    end
    | None ->
        let result = fibonacci (n - 1) + fibonacci (n - 2) in
        state := (n, result) :: !state;
        result

let () =
  Dream.run @@ fun request ->
  match Dream.query "n" request with
  | Some message ->
      let result = string_of_int @@ fibonacci @@ int_of_string message in
      let count = List.length !state in
      Dream.respond @@ "The fibonacci of " ^ message ^ " is " ^ result
      ^ " and memo has " ^ string_of_int count ^ " items"
  | None -> Dream.respond "Please ask for a number"