On Tuesday, June 23, 2015 at 8:30:32 AM UTC-4, Matthew Flatt wrote: > Providing #f as the third argument to `local-expand` means that > > (+ i j) > > is expanded only as far as exposing the primitive function-call form, also > known as `#%plain-app`: > > (#%plain-app + i j) > > When `i` is encountered later, there's no binding in the compile-time > environment, because the internal-definition context has been > discarded as the `my-def-stx` macro returned. > > Probably you want to replace the `#f` with `null` (which means "expand > without stopping"). Got it - this makes sense, thanks.
> Another possibility is to expand to a > `letrec-syntaxes+values` form to bind `i` and `j`. This is actually what I'm trying to avoid - see the earlier note on why I need a solution that won't leave behind empty (let-values () ...) forms (or any other Racket-specific forms) in the output syntax. > At Tue, 23 Jun 2015 02:13:19 -0400, Thomas Dickerson wrote: > > I seem to be missing some key ingredient here. The following really simply > > test-case, using let-syntaxes, works as expected: > > > > > (define-syntax my-def-stx > > > (lambda (stx) > > > (syntax-case stx (my-def-stx) > > > [(my-def-stx (id ...) rhs expr) > > > #'(let-syntaxes ([(id ...) rhs]) expr)]))) > > > > > > (my-def-stx > > > (i j) (values (lambda (stx) #'3) (lambda (stx) #'4)) > > > (+ i j)) > > > > > Trying the same thing, but with this: > > > > > (require (for-syntax syntax/context)) > > > (define-syntax my-def-stx > > > (lambda (stx) > > > (syntax-case stx (my-def-stx) > > > [(my-def-stx (id ...) rhs expr) > > > (let* ([intdef (syntax-local-make-definition-context)] > > > [ctx (generate-expand-context)]) > > > (syntax-local-bind-syntaxes (syntax->list #'(id ...)) > > > (local-transformer-expand #'rhs 'expression null) intdef) > > > (internal-definition-context-seal intdef) > > > (local-expand #'expr ctx #f intdef))]))) > > > > > > (my-def-stx > > > (i j) (values (lambda (stx) #'3) (lambda (stx) #'4)) > > > (+ i j)) > > > > > instead, gives me "i: undefined; cannot reference an identifier before its > > definition". > > > > Thomas Dickerson > > > > Brown University > > Department of Computer Science > > 115 Waterman St, 4th Floor > > Providence, RI 02912 > > > > 802-458-0637 > > > > On Mon, Jun 22, 2015 at 11:39 PM, Matthew Flatt <mfl...@cs.utah.edu> wrote: > > > > > Probably you don't want to work with namespaces, which are intended more > > > for run-time reflection. > > > > > > For an example of turning internal definitions into > > > 'letrec-syntaxes+values', try the implementation of 'racket/block'. > > > > > > > On Jun 23, 2015, at 10:06 AM, Thomas Dickerson < > > > thomas_dicker...@brown.edu> wrote: > > > > > > > > Update / addendum: I was also able to fairly trivially extend Alex's > > > code using let-syntax to have the more hygienic behavior for where Accum > > > is/is-not visible, but let-syntax ends up leaving an additional layer of > > > empty (let-values() ...) behind. > > > > > > > > The documentation for let-syntax makes the following claim - "The > > > evaluation of each trans-expr is parameterized to set current-namespace to > > > a namespace that shares bindings and variables with the namespace being > > > used to expand the let-syntax form, except that its base phase is one > > > greater." which seems very much related to what I'd like to accomplish > > > (and > > > Shriram's suggestion that I mentioned in the original post); however, I > > > see > > > no evidence of this actually taking place in the Racket source-code, it > > > just appears to desugar, with very few bells and whistles, to > > > letrec-syntaxes+values which evidently is implemented in the C code. > > > Digging into syntax-parameterize shows that, unsurprisingly, this is also > > > how syntax-parameterize gets desugared, with a few more bells and > > > whistles. > > > > > > > > So I guess at this point the remainder of my question boils down to > > > this: can someone offer any insight into the process of turning macros > > > which are introduced by let-syntax or equivalent into macros which are > > > introduced implicitly by an internal-definition-context argument to > > > local-expand, or by explicit namespace manipulation as hinted at in the > > > let-syntax documentation (but which I can't turn up anywhere). > > > > > > > >> On Monday, June 22, 2015 at 5:35:50 PM UTC-4, Thomas Dickerson wrote: > > > >> Thanks for the effort that went into figuring that out! A couple first > > > thoughts on the implementation: > > > >> To first order, this is exactly what I want to be able to do (and it > > > elegantly avoids local-expand by reasoning about expansion order); > > > however, > > > as a general pattern, it's a bit unhygienic in that Accum is now in the > > > global namespace, which precludes using it as a child macro for other > > > constructs, and prevents specific instantiations of Loop from requesting a > > > different name for Accum to cooperate in nested loops. > > > >> > > > >> I also noticed that (syntax-parameterize) isn't totally transparent in > > > the expanded syntax - it leaves a bunch of empty (let-values () ...) > > > behind, which is fine for Racket, but problematic in my target use-case of > > > emitting something which ultimately needs to be an entirely different > > > language. This is why my experiments have all involved local-expand - I > > > want to introduce expand-time names without introducing wrapping > > > let-syntaxes (or similar) forms around my body code. > > > >> > > > >> > > > >>> On Saturday, June 20, 2015 at 2:24:40 PM UTC-4, Alex Knauth wrote: > > > >>>> On Jun 19, 2015, at 7:44 PM, Thomas Dickerson < > > > thomas_dicker...@brown.edu> wrote: > > > >>>> > > > >>>> I was intending for that example to have the variables be defined > > > outside the macro, but being able to create the (set! ...) forms outside > > > should mean I could also hypothetically create let/define-values forms. > > > This is why I originally specified being able to effect generation of both > > > prologue + epilogue code. > > > >>> > > > >>> I figured this out for code that will be expanded after the body: > > > >>> > > > >>> #lang racket/base > > > >>> > > > >>> (require racket/stxparam > > > >>> (for-syntax racket/base > > > >>> syntax/parse > > > >>> racket/set > > > >>> )) > > > >>> > > > >>> ;; (syntax-parameter-value vars) : (U #f (MutableSetof Identifier)) > > > >>> (define-syntax-parameter vars #f) > > > >>> > > > >>> (define-syntax Accum > > > >>> (lambda (stx) > > > >>> (syntax-parse stx > > > >>> [(Accum x:id dx:expr) > > > >>> (define vs (syntax-parameter-value #'vars)) > > > >>> (unless (set-mutable? vs) > > > >>> (raise-syntax-error #f "cannot be used outside Loop" stx)) > > > >>> (set-add! vs (syntax-local-introduce #'x)) > > > >>> #'(set! x (+ x dx))]))) > > > >>> > > > >>> (define-syntax set-accums-zero! > > > >>> (syntax-parser > > > >>> [(set-accums-zero!) > > > >>> #:with [x ...] > > > >>> (map syntax-local-introduce (set->list (syntax-parameter-value > > > #'vars))) > > > >>> #'(begin (set! x 0) ...)])) > > > >>> > > > >>> (define-syntax Loop > > > >>> (syntax-parser > > > >>> [(Loop up-to-expr:expr body:expr ...+) > > > >>> #'(syntax-parameterize ([vars (mutable-set)]) > > > >>> (let ([up-to up-to-expr]) > > > >>> (letrec > > > >>> ([loop > > > >>> (lambda (n) > > > >>> body > > > >>> ... > > > >>> (if (< n up-to) > > > >>> (loop (add1 n)) > > > >>> (void)))]) > > > >>> (set-accums-zero!) > > > >>> (loop 0))))])) > > > >>> > > > >>> (let ([x "x"] [y "y"] [z "z"]) > > > >>> (Loop 10 > > > >>> (begin > > > >>> (define-values > > > >>> [dx dy dz] > > > >>> (values 1 2 3)) > > > >>> (printf "x = ~v, y = ~v, z = ~v\n" x y z) > > > >>> (Accum x dx) > > > >>> (Accum y dy) > > > >>> (Accum z dz)))) > > > >>> > > > >>> To generate a let outside of that you’d probably need to do some kind > > > of local-expand, but I’m not sure. > > > > > > > > -- > > > > 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 racket-users+unsubscr...@googlegroups.com. > > > > 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 racket-users+unsubscr...@googlegroups.com. > > 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. 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