(define play-nim
  (lambda (game-state player)
    (display-game-state game-state)
    (if (game-over? game-state) 
        (announce-winner game-state player)
        (let ((move (next-move game-state player)))
          (announce-move player move)
          (play-nim (apply-move move game-state) (other-player player))))))

(define next-move
  (lambda (game-state player)
    (if (equal? player 'human)
        (human-move game-state)
        (computer-move game-state))))

(define other-player
  (lambda (player)
    (if (equal? player 'human)
        'computer
        'human)))

(define computer-move
  (lambda (game-state)
    (if (> (car game-state) 0)
        (cons 1 1)
        (cons 2 1))))

(define prompt
  (lambda (prompt-string)
    (display prompt-string)
    (newline)
    (read)))

(define human-move
  (lambda (game-state)
    (let ((pile (prompt "Which pile will you remove from?")))
      (let ((n-coins (prompt "How many coins do you want to remove?")))
        (cons pile n-coins)))))

(define game-over?
  (lambda (game-state)
    (and (= 0 (car game-state))
         (= 0 (cdr game-state)))))

(define announce-winner
  (lambda (game-state player)
    (let ((winner (other-player player)))
      (if (equal? winner 'human) 
          (display "You win. Congratulations.")
          (display "You lose. Better luck next time."))
      (newline))))

(define display-game-state
  (lambda (game-state)
    (display "    Pile 1: ")
    (display (car game-state))
    (newline)
    (display "    Pile 2: ")
    (display (cdr game-state))
    (newline)))

(define announce-move
  (lambda (player move)
    (if (equal? player 'human)
        (display "You")
        (display "I"))
    (display " take ")
    (display (car move))
    (display " coins from pile ")
    (display (cdr move))
    (display ".")
    (newline)))

(define apply-move
  (lambda (move game-state)
    (let ((pile (car move))
          (n-coins (cdr move)))
      (if (= pile 1)
          (cons (- (car game-state)
                   n-coins) 
                (cdr game-state))
          (cons (car game-state)
                (- (cdr game-state)
                   n-coins))))))