Can't you just delete the whole second binding for accs? Sam <div class="gmail_quote">On Jul 3, 2014 8:11 PM, "Jens Axel Søgaard" <<a href="mailto:jensaxel@soegaard.net">jensaxel@soegaard.net</a>> wrote: <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"> Thanks to all for the advice. It seems the following version of match works for Whalesong: <a href="https://github.com/soegaard/whalesong-libs" target="_blank">https://github.com/soegaard/whalesong-libs</a> 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 <<a href="mailto:samth@cs.indiana.edu">samth@cs.indiana.edu</a>>: > 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 <<a href="mailto:jensaxel@soegaard.net">jensaxel@soegaard.net</a>> 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: >> <a href="http://lists.racket-lang.org/users" target="_blank">http://lists.racket-lang.org/users</a> -- -- Jens Axel Søgaard </blockquote></div>