Oops, sorry, I accidentally clicked "send" button before adding any contents. This one is the real reply.

On Sat, Jun 10, 2017 at 6:56 AM, Marc Nieper-Wißkirchen <xxxxxx@nieper-wisskirchen.de> wrote:

We could also demand from the procedural layer of SRFI 99 that the procedure returned by `(rtd-accessor rtd field)` is always the same. Then we can use `eq?` to match accessors used in child constructors against parent fields (by simply looping through all the fields.

Yes, this is an option I'm thinking for my implementation.

In abstract terms, I'm thinking along the line to ask implementations to provide some means to map accessor name identifiers into implementation-dependent "field designator", and make make-rtd / rtd-constructor work on them. Such mapping may need to access information available in macro expansion time, so it's beyond the scope of procedural layer. The point is to make the information to specify fields other than field names available in the procedural layer through somewhat agreed API.