> On Mar 14, 2018, at 2:41 PM, 'Leandro Facchinetti' via Racket Users
> <[email protected]> wrote:
>
>
> What if you wrote macros over reduction-relation instead of the exact model?
> These macros could implement threading and hide it. They would kind of be
> like monads here. — Matthias
>
> Do you mean something like
>
> (define-parameterized-metafunction (k) L
> tick : e _ _ _ t -> t
> [(tick e _ _ _ t) ,(take (cons (term e) (term t)) k)])
>
> which would expand to
>
> (define-metafunction L
> tick : e _ _ _ t _ -> t
> [(tick e _ _ _ t k) ,(take (cons (term e) (term t)) k)])
>
> ?
>
> How would the call sites of the metafunction know it expects the extra
> argument?
>
> --
> 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.
More like below. This one is imperative, but you could easily imagine a state
definition of (—> (lhs t) (rhs ,(+ t 1))) in the macro. But I haven’t thought
about how to access the tick value then. Once you have the macro you want, you
probably want to submit a PR to Robby so that it gets baked in or make a design
change proposal. Does this make more sense? — Matthias
#lang racket
(require redex)
(require (for-syntax syntax/parse))
(define-syntax (r-r/tick stx)
(syntax-parse stx
[(_ PL ((~literal -->) lhs rhs) ...)
#'(begin
(initialize!)
(reduction-relation
PL
(--> lhs rhs
(where _ ,(displayln `(tick# ,(update!) for ,(term rhs)))))
...))]))
(define ticks (make-parameter 0))
(define (initialize!) (ticks 0))
(define (update!) (ticks (+ (ticks) 1)) (ticks))
; -----------------------------------------------------------------------------
(define-language X
(e ::= a b c))
(define go
(r-r/tick
X
(--> a b)
(--> b c)
(--> c a)))
(traces go (term a))
--
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.
