; guess the number
(define rand #f)
(define randint #f)
(let ((two31 #x80000000) (a (make-vector 56 -1)) (fptr #f))
(define (mod-diff x y) (modulo (- x y) two31)) ; generic version
; (define (mod-diff x y) (logand (- x y) #x7FFFFFFF)) ; fast version
(define (flip-cycle)
(do ((ii 1 (+ ii 1)) (jj 32 (+ jj 1))) ((< 55 jj))
(vector-set! a ii (mod-diff (vector-ref a ii) (vector-ref a jj))))
(do ((ii 25 (+ ii 1)) (jj 1 (+ jj 1))) ((< 55 ii))
(vector-set! a ii (mod-diff (vector-ref a ii) (vector-ref a jj))))
(set! fptr 54) (vector-ref a 55))
(define (init-rand seed)
(let* ((seed (mod-diff seed 0)) (prev seed) (next 1))
(vector-set! a 55 prev)
(do ((i 21 (modulo (+ i 21) 55))) ((zero? i))
(vector-set! a i next) (set! next (mod-diff prev next))
(set! seed (+ (quotient seed 2) (if (odd? seed) #x40000000 0)))
(set! next (mod-diff next seed)) (set! prev (vector-ref a i)))
(flip-cycle) (flip-cycle) (flip-cycle) (flip-cycle) (flip-cycle)))
(define (next-rand)
(if (negative? (vector-ref a fptr)) (flip-cycle)
(let ((next (vector-ref a fptr))) (set! fptr (- fptr 1)) next)))
(define (unif-rand m)
(let ((t (- two31 (modulo two31 m))))
(let loop ((r (next-rand)))
(if (<= t r) (loop (next-rand)) (modulo r m)))))
(init-rand 19380110) ; happy birthday donald e knuth
(set! rand (lambda seed
(cond ((null? seed) (/ (next-rand) two31))
((eq? (car seed) 'get) (cons fptr (vector->list a)))
((eq? (car seed) 'set) (set! fptr (caadr seed))
(set! a (list->vector (cdadr seed))))
(else (/ (init-rand (modulo (numerator
(inexact->exact (car seed))) two31)) two31)))))
(set! randint (lambda args
(cond ((null? (cdr args))
(if (< (car args) two31) (unif-rand (car args))
(floor (* (next-rand) (car args)))))
((< (car args) (cadr args))
(let ((span (- (cadr args) (car args))))
(+ (car args)
(if (< span two31) (unif-rand span)
(floor (* (next-rand) span))))))
(else (let ((span (- (car args) (cadr args))))
(- (car args)
(if (< span two31) (unif-rand span)
(floor (* (next-rand) span))))))))))
(define (show . msg) (for-each display msg))
(define (show-line . msg) (apply show msg) (newline))
(define (get-yes-no)
(let ((answer (char-downcase (string-ref
(symbol->string (read)) 0))))
(if (member answer '(#\y #\n)) answer
(begin (show-line "Please answer yes or no.")
(get-yes-no)))))
(define (human-plays limit)
(let ((n (randint 1 limit)))
(show-line "I am thinking of a number from 1 to " limit)
(display "What is your guess? ")
(let loop ((g (read)) (k 0))
(cond ((< g n)
(show-line "Your guess is less than my number.")
(show "What is your next guess? ")
(loop (read) (+ k 1)))
((< n g)
(show-line "My number is less than your guess.")
(show "What is your next guess? ")
(loop (read) (+ k 1)))
(else
(show-line "You guessed my number "
n " in " k " tries!")
k)))))
(define (computer-plays limit)
(show-line "Think of a number from 1 to " limit ".")
(let loop ((lo 1) (hi limit) (k 0))
(let ((mid (quotient (+ lo hi) 2)))
(cond ((= lo mid)
(show-line "I guessed your number "
lo " in " k " tries.")
k)
(else (show "Is your number less than " mid "? ")
(case (get-yes-no)
((#\y) (loop lo mid (+ k 1)))
((#\n) (loop mid hi (+ k 1)))))))))
(define (play limit)
(show-line "Let's play Guess-The-Number!")
(show-line "You go first.")
(let ((k-human (human-plays limit)))
(show-line "Now it's my turn.")
(let ((k-computer (computer-plays limit)))
(cond ((< k-human k-computer)
(show-line "You made less guesses than me.")
(show-line "You win! Congratulations!"))
((< k-computer k-human)
(show-line "I made less guesses than you.")
(show-line "I win. Better luck next time!"))
(else
(show-line "We both made the same number of guesses.")
(show-line "The game is a tie. Good game!")))
(show "Would you like to play again? ")
(if (char=? (get-yes-no) #\y)
(play limit)
(show-line "Thanks for playing! Good-bye!")))))
(play 100)