Anyone up for a dissertation? Multi-stepping debugging is, eh, pushing it.
On Jan 19, 2011, at 2:43 PM, Doug Orleans wrote:
> The following program was a puzzle in the 2011 MIT Mystery Hunt held last
> weekend. (I'm not linking directly to the site because they posted a
> solution and I don't want you to be tempted to look at the answer
> prematurely...) I was disappointed that Dr Racket doesn't seem to have a
> multi-threaded stepping debugger, at least not in a form that could easily
> run this program-- correct me if I'm wrong.
>
> I would be interested to hear what other ideas people have about solving this
> puzzle, either automatically or by hand (or some combination). But, I
> haven't solved it myself yet, so I may be avoiding reading replies for a
> while...
>
> --Doug
>
>
>
> Efficiency
> The Prince is quite proud of his competitive Katamari-rolling time record,
> having mastered the art of multitasking.
>
> All procedure calls are evaluated from left to right.
>
>
>
>
>
> (define (send x)
> (if (or (integer? x) (char? x))
> (display x)
> (send x))
> (flush-output)
> #t)
> (define (sendc x)
> (if (and (>= x 0) (< x 26))
> (send (integer->char (+ 65 x)))
>
>
> (sendc x)))
>
>
> (define a 2)
> (define b '(11))
> (define c 5)
> (define d 30)
> (define e 3)
>
> (thread
> (lambda ()
>(set! a (* a (first a)))
>(send a)
>(set! c (lambda () (- b 4)))
>
>
>(set! c (lambda () (- b 11)))
>
>(set! d (rest d))
>(sendc (/ 4 (+ (- c) c)))
>(set! a (sqrt (+ c (* c c
>(sendc b)
>(set! b '(((24 12 15 (2))) 1 (5 1) 3 2 8 10 (9 1 (3)) ((3) (1)) 5 14 10))
>
>
>(set! d '())
>
>(sendc (length (append c b)))
>(sendc (length (append a b c c c d)))
>(set! d 2)
>(map (lambda (x)
> (set! c (first b))
> (sendc x)
> (set! b c)) a)
>
>
>(send (* (+ 3 (first c)) 100 (- (sqrt a) 1)))
>
>(set! a (+ a 1))
>(set! e (- e 1))
>))
>
> (thread
> (lambda ()
>(set! a (list c))
>(set! a (lambda (x) (if x (sendc x) x)))
>(let loop ()
>
>
> (set! b (c))
>
> (if (a b)
> (loop)
> (set! d '(2 4 8 16 32
>(set! c (first d))
>(set! c (second d))
>(set! b (- a (sqrt (first d
>(set! a (list 14 (- (length b) 1) c))
>
>
>(let loop ()
>
> (set! d b)
> (if (null? d)
> (set! a (+ a 1))
> (begin
>(sendc (first d))
>(set! b (rest d))
>(loop
>(set! e (- e 1))
>))
>
>
>
>
> (thread
> (lambda ()
>(set! b d)
>(set! c (lambda () (/ b 2)))
>(let loop ()
> (set! d (- d 10))
> (if (and (= d 0)
> (= b 0)
> (< b 0))
> (set! b #f)
>
>
> (loop)))
>
>(set! c (first d))
>(set! a 0)
>(sendc (length b))
>(set! c (list (second b)))
>(sendc (sqrt (+ 12 (length d
>(send (+ (/ (foldl * 26 a)
>(+ (length (append a b))
>
>
> (* (length c) (length c
>
> d))
>(set! a (first b))
>(sendc (/ 204 a))
>(set! e (- e 1))
>))
>
> (let loop ()
> (if (> e 0)
> (loop)
> (newline)))
>
> _
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