Based on the documentation, I thought that the right answer would be `(list (gensym))` but that didn't work -- hopefully someone else knows.
Sam On Tue, Jun 23, 2015 at 4:43 PM, Thomas Dickerson <thomas_dicker...@brown.edu> wrote: > I thought that might be the case, but the documentation is pretty dense (and > self-referential), so it's not clear what the correct value for that > argument is. > > Thomas Dickerson > > Brown University > Department of Computer Science > 115 Waterman St, 4th Floor > Providence, RI 02912 > > 802-458-0637 > > On Tue, Jun 23, 2015 at 3:57 PM, Sam Tobin-Hochstadt <sa...@cs.indiana.edu> > wrote: >> >> To fix your last issue, you probably want to provide a different value as >> the `context-v` argument (the 2nd one) to `local-expand`. >> >> Sam >> >> On Tue, Jun 23, 2015 at 3:46 PM Thomas Dickerson >> <thomas_dicker...@brown.edu> wrote: >>> >>> Okay - for posterity's sake, here's an updated version of Alex's code >>> that supports nested Loop/Accum, and doesn't leave any "syntactic residue" >>> after expansion. This is now what I set out to accomplish with my original >>> set of questions: >>>> >>>> #lang racket/base >>>> >>>> (require racket/stxparam >>>> (for-syntax racket/base >>>> >>>> racket/set >>>> racket/syntax >>>> syntax/parse >>>> syntax/stx >>>> syntax/context)) >>>> >>>> (define-syntax Loop >>>> (lambda (stx) >>>> (syntax-parse stx >>>> [(Loop accum-id:id up-to-expr:expr body:expr ...+) >>>> (let* ([defs (syntax-local-make-definition-context)] >>>> [ctx (generate-expand-context)]) >>>> (syntax-local-bind-syntaxes >>>> (list #'accum-id) >>>> (local-transformer-expand >>>> #'(let ([vars (mutable-set)]) >>>> (lambda ([stx #f]) >>>> (if (syntax? stx) >>>> (syntax-parse stx >>>> [(accum-id x:id dx:expr) >>>> (set-add! vars (syntax-local-introduce #'x)) >>>> >>>> >>>> #'(set! x (+ x dx))]) >>>> >>>> vars))) 'expression null) defs) >>>> (internal-definition-context-seal defs) >>>> (with-syntax* ([(body ...) >>>> (stx-map >>>> (lambda (body) >>>> (with-syntax ([body body]) >>>> (local-expand #'body ctx null defs))) >>>> #'(body ...))] >>>> [(init ...) >>>> (map >>>> (lambda (var) >>>> (with-syntax ([var (syntax-local-introduce >>>> var)]) #'(set! var 0))) >>>> (set->list >>>> ((syntax-local-value >>>> (internal-definition-context-apply defs >>>> #'accum-id) >>>> #f defs))))]) >>>> #'(let ([up-to up-to-expr]) >>>> >>>> >>>> (letrec >>>> ([loop >>>> (lambda (n) >>>> body ... >>>> >>>> (let ([n (add1 n)]) >>>> (if (< n up-to) >>>> (loop n) >>>> (void))))]) >>>> init ... >>>> (loop 0)))))] >>>> >>>> >>>> [(Loop up-to-expr:expr body:expr ...+) >>>> >>>> (with-syntax >>>> ([Accum (datum->syntax stx 'Accum)]) >>>> #'(Loop Accum up-to-expr body ...))]))) >>>> >>>> (let ([x (void)] [y (void)] [z (void)]) >>>> (Loop 2 >>>> (let ([dx 1] [dy 2] [dz 3]) >>>> (Accum x dx) >>>> (Loop AccumInner 2 >>>> >>>> >>>> (printf "x = ~v, y = ~v, z = ~v\n" x y z) >>>> >>>> (Accum y dy) >>>> (AccumInner z dz))))) >>> >>> >>> One last question - the change to using local-expand meant that the loop >>> body was no longer happy accepting define-values forms and raised "Not in a >>> definition context" errors. I can use let to accomplish the same thing >>> without any problems, but if someone could explain what changes would need >>> to be made to the local-expand call for that to work, I'd be grateful (for >>> my own understanding). >>> >>> >>> Thomas Dickerson >>> >>> Brown University >>> Department of Computer Science >>> 115 Waterman St, 4th Floor >>> Providence, RI 02912 >>> >>> 802-458-0637 >>> >>> On Tue, Jun 23, 2015 at 11:17 AM, Thomas Dickerson >>> <thomas_dicker...@brown.edu> wrote: >>>> >>>> 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. >>> 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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