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

A relevant side-comment is that this is a popular way for implementing
tail-calls:

  http://en.wikipedia.org/wiki/Tail_call#Through_trampolining



20 minutes ago, Galler wrote:
> 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!

-- 
          ((lambda (x) (x x)) (lambda (x) (x x)))          Eli Barzilay:
                    http://barzilay.org/                   Maze is Life!