> On Aug 30, 2019, at 1:19 AM, Philip McGrath <phi...@philipmcgrath.com> wrote:
>
> Hi Kevin,
>
> This is interesting! A number of people have wanted conveniences around
> `keyword-apply` and accepting the same keywords as some other function. (The
> trouble is, different people have different ideas of what those conveniences
> should be.)
>
> To start with, I had a few small suggestions about the code you sent:
> `keyword-apply/filter` doesn't need to be a macro, and your macro should use
> `fn` rather than `h`;
> the second result of `procedure-keywords` can be `#f` if the given procedure
> accepts all keywords;
> `for/lists` might be more convenient than `for/fold`;
> I think some of the cases in `filter/kw` get the filtering backwards;
> keywords can be `quote`-ed as values, so you don't need so many
> symbol-to-string-to-keyword conversions;
> using `set!` this way will cause lots of problems;
> there's no need for `list->vector` in `get-kw-val`; and
> in `def`, it might be better to use syntax parameters than to break hygiene.
> You may know this, but all keyword-accepting functions in Racket are
> effectively implemented with `make-keyword-procedure`: the variants of
> `lambda` and `define` that use `kw-formals` are macros that expand to more
> primitive versions that don't know about keywords. The macros also do some
> optimization where possible. For inspiration, you might be interested in the
> implementation in
> https://github.com/racket/racket/blob/master/racket/collects/racket/private/kw.rkt
>
> <https://github.com/racket/racket/blob/master/racket/collects/racket/private/kw.rkt>
>
> For fun, I wrote a version that illustrates some of these suggestions and and
> tries to do more work at compile-time. Be warned that it is not thoroughly
> tested! I'm pasting it below, and I've also put it up as a Gist at
> https://gist.github.com/LiberalArtist/292b6e99421bc76315110a59c0ce2b0d
> <https://gist.github.com/LiberalArtist/292b6e99421bc76315110a59c0ce2b0d>
>
> -Philip
Hi Philip,
I’ve been using your kw-pass-through-lambda.rkt module quite happily for a
while now. One issue I’ve run into though is that the local-keyword-apply
appears to have an issue when the return is multiple values. For instance, in
the test module, if you replace the:
(define (h #:c c . x)
(list c x))
With:
(define (h #:c c . x)
(values c x))
You’ll get an error: “Returned two values to single value return context”
Is there a way to fix this?
Kevin
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