[racket] Finite State Machines of Arbitrary Size using Racket's composable control

Y, that's closer to what I had in mind.


On Thu, May 24, 2012 at 1:18 PM, Eli Barzilay wrote:

> Just now, Galler wrote:
>> Eli,
>>
>> I fully agree with you that any FSM is equivalent to functional 
>> composition and can be implemented in the manner you show.
>>
>> However , in the way you've implemented the signal-handlers
>>
>>   (define (B i)
>>>       (if (= 0 (get i))
>>>         (begin (printf "~s)" (sub1 i))
>>>                (next A i))
>>
>> I believe you have the signal handler B both reading the signal (get 
>> i) and advancing to the next position in the signal-stream (next A i)
>
> IIUC, you could do that with something like this:
>
>   (define (encode v)
>     (define (get i) (vector-ref v i))
>     (define last (sub1 (vector-length v)))
>     (define (next S i) (when (< i last) (S (add1 i))))
>     (define (B signal i)
>       (if (= 0 signal)
>         (begin (printf "~s)" (sub1 i))
>                A)
>         B))
>     (define (A signal i)
>       (if (= 0 signal)
>         A
>         (begin (printf "(~s " i)
>                B)))
>     (for/fold ([state A]) ([signal (in-vector v)] [i (in-naturals)])
>       (state signal i)))
>
> But it seems redundant since the abstraction was practically there in
> `next'.
>
> -- 
>           ((lambda (x) (x x)) (lambda (x) (x x)))          Eli 
> Barzilay:
>                     http://barzilay.org/                   Maze is 
> Life!