Marc,

>> - In many macro systems, a syntax transformer is just a procedure
>> (taking a syntax object and returning one). It is unclear how a useful
>> `syntax-transformer?` could be defined. Moreover, in R7RS,
>> `syntax-rules` is not a keyword introducing an expression form so
>> syntax transformers are not first-class objects.
>
> syntax-transformer? can be defined as ##sys#macro? on Chicken or as
> location-tracking code on other implementations, like I noted above.

Update: ##sys#macro? was removed, but it shows a precedent. I remember
some other implementation having #<macro ...> object, but I don’t
remember which.

Thanks,
--
Artyom Bologov
https://aartaka.me