Am Sa., 7. März 2020 um 14:45 Uhr schrieb Lassi Kortela <xxxxxx@lassi.io>:

The `fox` procedure would make a wonderful case study for keyword
arguments in SRFIs, if we can come to an agreement on how to do them.

The answer here is SRFI 159/166. :)

That said, if Scheme wasn't expressive enough for such a combinator language, keywords would have come handy for a procedure like `fox'.  So this is also a wonderful case study for general keyword arguments vs some tailored DSL.