open System

/// Union of possible choices for a round of rock-paper-scissors
type Choice =
| Rock
| Paper
| Scissors

/// Gets the string representation of a Choice
let getString = function
   | Rock -> "Rock"
   | Paper -> "Paper"
   | Scissors -> "Scissors"

/// Defines rules for winning and losing
let beats (a : Choice, b : Choice) =
   match a, b with
   | Rock, Scissors -> true    // Rock beats Scissors
   | Paper, Rock -> true       // Paper beats Rock
   | Scissors, Paper -> true   // Scissors beat Paper
   | _, _ -> false

let genMove =
    Scissors

/// Gets the move chosen by the player
let rec getMove() =
   printfn "Rock, Paper, Scissors"
   printf "Please enter your choice: "
   let choice = Console.ReadLine ()
   match choice with
   | "rock" | "Rock" -> Rock
   | "paper" | "Paper" -> Paper
   | "scissors" | "Scissors" -> Scissors
   | _ ->
       printf "Invalid choice.\n\n"
       getMove ()

/// Place where all the game logic takes place.
let rec game() =
   let computer = genMove
   let player = getMove()
   Console.WriteLine ("Player: {0} vs Computer: {1}", getString player, getString computer)
   Console.WriteLine (
       if beats(player, computer) then "Player Wins!\n"
       elif beats(computer, player) then "Computer Wins!\n"
       else "Draw!\n"
   )
   game()

game()