(play-with-turns (make-game-state 5 8) 'humman)
Q: What would happen?
A: If all cond tests fail, the behavior is unspecified.
play-with-turns should do error handling:
(define play-with-turns
(lambda (game-state player)
(cond
((over? game-state) (announce-winner player))
((equal? player 'human)
(play-with-turns (human-move game-state) 'computer))
((equal? player 'computer)
(play-with-turns (computer-move game-state) 'human))
(else (error "player wasn't human or computer:" player)))))