So I was reading The Princess Bride today...

BattleofWits.scm

(define (generic-agent put drink survive) (lambda (arg)
                                            (cond ((null? arg) put) ;; output a glass to put poison into
                                                  ((boolean? arg) (survive arg)) ;; output whether you survive given poison
                                                  ((procedure? arg) (drink arg)) ;; output a glass to drink given the other player's source
                                                  (else (error "Input type must be one of: Null, boolean, or procedure")))))

(define (contains? list element) (if (member element list) #t #f))
(define (battle-of-wits p1 p2)
  (define p1lives (not (p1 (contains? (p1 '()) ;;contains returns whether the glass chosen has poison in it
                                 (cond ((=  (p2 p1) 1 ) 2) ;; this cond chooses whichever glass the other player didn't
                                       ((= (p2 p1) 2) 1)
                                       (else (error "...he drank WHAT?")))))))
  (define p2lives (not (p2 (contains? (p1 '()) (p2 p1)))))
  (cond ((and p1lives p2lives) "They both lived! Some game of death that was...")
        (p1lives "Player one lives! True love prevails, maybe?")
        (p2lives "Player 2 lives! Presumably, the Princess will not.")
        (else "Everybody dies. Hamlet.")))

(define fezzik (generic-agent
                (list 1)
                (lambda (otherplayer) 1)
                (lambda (given-poison) given-poison)))

(define aristotle (generic-agent
                (list 2)
                (lambda (otherplayer) 2)
                (lambda (given-poison) given-poison)))

(define vizzini (generic-agent
                 (list (+ (random 2) 1)) ;; chooses at random to avoid prediction
                 (lambda (otherplayer)
                   (cond ((contains? (otherplayer '()) 1) 2)
                         ((contains? (otherplayer '()) 2) 1)
                         (else (error "INCONCEIVABLE!"))))
                 (lambda (given-poison) given-poison)))

(define dread-pirate-roberts (generic-agent
                              (list 1 2)
                              (lambda (otherplayer) (+ (random 2) 1))
                              (lambda (given-poison) #f)))

(battle-of-wits dread-pirate-roberts vizzini)