(* Program.fs *)
module Program

open Microsoft.FSharp.Control
open System
open Telegram.Bot
open Telegram.Bot.Types.Enums

let bot_token = "token"
let bot = TelegramBotClient(bot_token)

let handler =
    new EventHandler<Args.MessageEventArgs>(
        fun obj x -> MessageProcessor.messageHandler (obj :?> TelegramBotClient) x
    )

[<EntryPoint>]
let main argv =
    bot.OnMessage.AddHandler(handler)
    bot.StartReceiving()
    ignore <| Console.ReadLine()
    bot.StopReceiving()
    0


(* MessageProcessor.fs *)
module MessageProcessor

open Telegram.Bot
open Telegram.Bot.Args
open Telegram.Bot.Types.Enums


let private greeting (client: TelegramBotClient) (chatId: Types.ChatId) =
    client.SendTextMessageAsync(chatId, "Nice to meet ya!")

let private commands = Map ["/start", greeting;]

let private proccessText (bot: TelegramBotClient) (msg: Types.Message) =
    let cmd = commands.TryFind msg.Text
    ignore <| if cmd.IsSome then cmd.Value bot (Types.ChatId msg.Chat.Id)
              else bot.SendTextMessageAsync(Types.ChatId msg.Chat.Id, "Some error")

let messageHandler obj (args : MessageEventArgs) =
    let bot = obj :> TelegramBotClient
    match args.Message.Type with
    | MessageType.TextMessage -> proccessText bot args.Message
    | _ -> ()