Robby’s message dominates mine but I don’t get why you can’t work your way thru what I provided.
> On Mar 15, 2018, at 9:22 AM, 'Leandro Facchinetti' via Racket Users > <[email protected]> wrote: > > > > 1. The cache for the reduction relation is invalid. > > > How so? > > > (apply-reduction-relation go (term a)) ;; => (the clock is 96) > (apply-reduction-relation go (term a)) ;; => (the clock is 99) > > The user hasn’t changed any parameters, but the results are different. The > second call didn’t go through the cache as it was supposed to. HUH? This is something that you control with the initialization function. The REDEX results are the same. It is up to your init function to cache or not cache. > > 2. There’s no way to parameterize ‘clock’ when calling the reduction > > relation (I think it’d really help to think of ‘k’ instead of ‘clock’). > > That’s what #:initial gives you. > > No, ‘#:initial’ let’s you parameterize ‘clock’ when *defining* the reduction > relation (‘r-r/tick’), not when *calling* it (‘traces’, > ‘apply-reduction-relation’ and friends). Really? (define *foo 0) (define (init) .. *foo ..) > > > 3. ‘clock’ isn’t available to metafunctions called from the reduction > > relation. > > > Give me an example. > > Sure. Let the reduction relation depend on the metafunction > ‘my-metafunction’, which uses ‘clock’: > > #lang racket > > (require redex) > (require (for-syntax syntax/parse)) > > (define-syntax (r-r/tick stx) > (syntax-parse stx > [(_ PL #:domain x #:initial go #:observe o #:update u ((~literal -->) lhs > rhs) ...) > #'(let ((clock (go))) > (reduction-relation > PL > #:domain x > (--> lhs rhs (where _ ,(begin (set! clock (u clock)) (o clock)))) > ...))])) > > ; > ----------------------------------------------------------------------------- > > (define-language X > (e ::= a b c)) > > (define-metafunction X > [(my-metafunction _) clock]) ;; <= ‘clock’ is just a symbol here, not a > bound (meta-)variable What does this even mean? Racket-Redex is about variables not symbols. — Matthias > > (define go > (r-r/tick > X > #:domain e > #:initial (lambda () (random 100)) > #:observe (lambda (clock) (displayln `(the clock is ,clock))) > #:update (curry + 3) > (--> a b) > (--> b (my-metafunction c)) > (--> c a))) > > (traces go (term a)) > > > > > * * * > > The point I’m bringing up is “Parameterized Redex models,” which I don’t > think is exactly the “state monad.” I guess I could hack my way with the > state monad if that’s all I had, but it’s too big a hammer because the > “state” never changes throughout a series of steps. Coming back to the > original example of ‘tick’, I’m not interested in abstracting time-stamp > tracking from the abstract machine (CESKₜ); I’m interested in abstracting the > implicit variable ‘k’ from the *abstract* abstract machine (CESKₜ^). I choose > ‘k’ before I start the machine, and then it remains constant throughout > evaluation. > > -- > You received this message because you are subscribed to the Google Groups > "Racket Users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
