hello lemon (todo)

Server.fs

module Server
 
open Lemon
open System.Collections.Generic
 
let todolist = ResizeArray<string>()

let (|Int|_|) (str: string) =
  match System.Int32.TryParse(str) with
  | true, x -> Some x
  | _ -> None

let (server:Server) = function
  | GET(Url []) -> 
      let res = Seq.mapi (fun i todo -> i.ToString() + ":" + todo) todolist
      ok >> response (String.concat "\n" res)
  | GET(Url ["add"; todo]) -> 
      todolist.Add(todo)
      ok >> response ("added " + todo)
  | GET(Url [Int id; "edit"; todo]) ->
      let before = todolist.[id]
      todolist.[id] <- todo
      ok >> response ("updated " + id.ToString() + ":" + before +  " -> " + todo)
  | GET(Url [Int id; "delete"]) ->
      todolist.RemoveAt(id)
      ok >> response ("deleted " + id.ToString())
  | _ -> notFound