[racket] A safe version of unsafe-struct-ref [for Whalesong]

Can't you just delete the whole second binding for accs?

Sam
On Jul 3, 2014 8:11 PM, "Jens Axel Søgaard" <jensaxel at soegaard.net> wrote:

> Thanks to all for the advice. It seems the following version of match
> works for Whalesong:
>
>     https://github.com/soegaard/whalesong-libs
>
> Admitted I have only made superfical tests.
>
>
> In match/compiler.rkt I replaced
>
> (define (gen-clause k rows x xs esc)
>   <...>
>   ;; it's a structure
>
>     [(box? k)
>      ;; all the rows are structures with the same predicate
>      (let* ([s (Row-first-pat (car rows))]
>             [accs (Struct-accessors s)]
>             [accs (if (Struct-complete? s)
>                       (build-list (length accs) (λ (i) #`(λ (x)
> (unsafe-struct-ref x #,i))))
>                       accs)]
>             [pred (Struct-pred s)])
>        (compile-con-pat accs pred Struct-ps))]
>     <...>)
>
> with
>
> (define (gen-clause k rows x xs esc)
>   <...>
>     ;; it's a structure
>     [(box? k)
>      ;; all the rows are structures with the same predicate
>      (let* ([s (Row-first-pat (car rows))]
>             [accs (Struct-accessors s)]
>             [accs (if (Struct-complete? s)
>                       (build-list (length accs)
>                                   (λ (i) (with-syntax ([a (list-ref accs
> i)])
>                                            #`(λ (x) (a x))))) ; [Whalesong]
>                       accs)]
>             [pred (Struct-pred s)])
>        (compile-con-pat accs pred Struct-ps))]
>     <...>)
>
> /Jens Axel
>
> 2014-07-03 15:12 GMT+02:00 Sam Tobin-Hochstadt <samth at cs.indiana.edu>:
> > The output of `match` when it uses `unsafe-struct-ref` can't be
> > faithfully implemented safely. In particular, `match` has access to
> > the accessor function, which may give you results that you can't get
> > from safe reflection such as `struct->vector`.
> >
> > Instead, I think you should just implement `unsafe-struct-ref` to look
> > inside the abstraction of structs, so that it violates the abstraction
> > in the same way that it does in Racket. While this won't potentially
> > crash in JavaScript, it will be unsafe relative to the abstractions of
> > Racket, and thus deserves the name unsafe.
> >
> > Sam
> >
> > On Wed, Jul 2, 2014 at 9:06 PM, Jens Axel Søgaard <jensaxel at soegaard.net>
> wrote:
> >> Is it possible to implement unsafe-struct-ref using safe constructs
> only?
> >>
> >> The reason behind this peculiar question, is that I am porting
> racket/match
> >> to Whalesong. The match compiler uses various unsafe constructs that
> Whalesong
> >> doesn't implement. It is straightforward to replace, say,
> >> unsafe-vector-ref with vector-ref.
> >>
> >> But unsafe-struct-ref ?
> >>
> >> It is okay to use all tricks in the book in phase 1 (Whalesong has
> >> restrictions in phase 0 only).
> >>
> >> /Jens Axel
> >> ____________________
> >>   Racket Users list:
> >>   http://lists.racket-lang.org/users
>
>
>
> --
> --
> Jens Axel Søgaard
>
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