Explicitly expanding `e` would ensure that the expansion work only has to
happen once, rather than twice. Even so, the fully-expanded syntax will be
expanded again in `syntax-local-bind-syntaxes` and in the expansion.
As far as I've seen, the only thing that liberal define contexts control is
whether definitions of functions that accept keyword arguments expand to a
normal `define-values` with runtime handling of keywords, or expand to a
collection of macros and function definitions that allow a more efficient
calling convention for first-order calls. The latter expansion doesn't work
for contexts like `class` where function definitions are re-interpreted in
a way that adds indirection, so it is only enabled in contexts that opt-in.
I see more bug in your macro: as its very first task, it should check if
`(syntax-local-context)` is `'expression`. If not, it should expand to
`(#%expression )`. This ensures that its expansion is
delayed until the second pass of the surrounding definition context so that
names bound by later definitions are available.
On Saturday, June 6, 2020 at 4:15:00 AM UTC-6, Sorawee Porncharoenwase
wrote:
>
> Ah, apparently I need syntax-local-identifier-as-binding. Here’s a
> revised code that passes the tests.
>
> (begin-for-syntax
> (define ((do-it gs ctx) e)
> (let loop ([e e])
> (define e-expanded (local-expand e
>(list gs)
>(list #'begin
> #'define-syntaxes
> #'define-values)
>ctx))
> (syntax-parse e-expanded
> #:literals (begin define-syntaxes define-values)
> [(begin body ...) #`(begin #,@(map loop (attribute body)))]
> [(define-values (x ...) e)
> #:with (x* ...) (map syntax-local-identifier-as-binding
> (attribute x))
> (syntax-local-bind-syntaxes (attribute x) #f ctx)
> #'(define-values (x* ...) e)]
> [(define-syntaxes (x ...) e)
> #:with (x* ...) (map syntax-local-identifier-as-binding
> (attribute x))
> (syntax-local-bind-syntaxes (attribute x) #'e ctx)
> #'(define-syntaxes (x* ...) e)]
> [e #'(set! acc (cons e acc))]
>
> Still not sure if there’s still anything wrong. In particular, do I need
> to expand e in define-syntaxes? And do I need to use
> prop:liberal-define-context for gs? (I don’t understand what liberal
> expansion is even after reading the docs several times) Both of these are
> done in the implementation of block, but without them, it seems to work
> equally well.
>
> On Fri, Jun 5, 2020 at 6:30 PM Sorawee Porncharoenwase <
> sorawe...@gmail.com > wrote:
>
>> Hi Racketeers,
>>
>> I’m creating a macro that collects values in the internal-definition
>> context. E.g.,
>>
>> ($list
>> 1
>> (define x 2)
>> x)
>>
>> should evaluate to '(1 2).
>>
>> Here’s my implementation, and it kinda works:
>>
>> #lang racket
>>
>> (begin-for-syntax
>> (define ((do-it gs ctx) e)
>> (let loop ([e e])
>> (define e-expanded (local-expand e (list gs) #f ctx))
>> (syntax-case e-expanded (begin define-syntaxes define-values)
>> [(begin body ...)
>> #`(begin #,@(map loop (syntax->list #'(body ...]
>> [(define-values ids e)
>> (begin
>>(syntax-local-bind-syntaxes (syntax->list #'ids) #f ctx)
>>e-expanded)]
>> [(define-syntaxes ids e)
>> (begin
>>(syntax-local-bind-syntaxes (syntax->list #'ids) #'e ctx)
>>#'(begin))]
>> [e #'(set! acc (cons e acc))]
>>
>> (define-syntax ($list stx)
>> (define gs (gensym))
>> (define ctx (syntax-local-make-definition-context))
>> (syntax-case stx ()
>> [(_ body ...)
>> #`(let ([acc '()])
>> #,@(map (do-it gs ctx) (syntax->list #'(body ...)))
>> (reverse acc))]))
>>
>> ($list 1
>>(define x 2)
>>x)
>>
>> There are problems though. If I change define to define2 as follows:
>>
>> (define-syntax-rule (define2 x y)
>> (define-values (x) y))
>>
>> ($list 1
>>(define2 x 2)
>>x)
>>
>> Then I get the “identifier used out of context” error. This doesn’t make
>> sense to me at all. My define2 should be very similar to define…
>>
>> There’s also another weird problem:
>>
>> ($list 1
>>(define-syntax (x stx) #'2)
>>x)
>>
>> The above works perfectly, but by wrapping x with #%expression, I get
>> the “identifier used out of context” error again.
>>
>> ($list 1
>>(define-syntax (x stx) #'2)
>>(#%expression x))
>>
>> What did I do wrong?
>>
>> Thanks!
>>
>
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