Am Fr., 1. Nov. 2019 um 20:44 Uhr schrieb Lassi Kortela <xxxxxx@lassi.io>:
>
> Can we have a quick vote about who prefers the current option 1:
>
> (keyword-lambda (a b (c d e)) <lambda body ...>)
>
> (keyword-call foo 1 2 (e 5 c 3 d 4))
>
> And who would prefer option 2 where all of these are supported:
>
> (keyword-lambda (a b :key c d e) <lambda body ...>)
>
> (keyword-call foo 1 2 e: 5 c: 3 d: 4)     ; In all Schemes
> (keyword-call foo 1 2 :e 5 :c 3 :d 4)     ; In all Schemes
> (keyword-call foo 1 2 #:e 5 #:c 3 #:d 4)  ; In Schemes that have #:
>
> Option 1 can be implemented with syntax-rules and tail patterns.
>
> Option 2 needs syntax-case, explicit-renaming, or define-macro. It can
> be implemented equally well in Schemes that have native read syntax for
> keywords, and Schemes that don't. The trick is to treat a symbol
> starting or ending with a colon as a keyword.

How do you want

(let ((:e 3))
  (keyword-call foo 1 2 :e 4))

being handled?

While Option 2 looks much better than Option 1, it doesn't seem to
work well when the underlying Scheme does not have a separate keyword
type (and keyword syntax).

So what about the following Option 3?

(keyword-call foo 1 2 : e 5)

In Schemes with a keyword reader syntax, it can be expressed as

(keyword-call foo 1 2 #:e 5)

Option 3 is also implementable using syntax-rules alone.