Thanks for the overview and detailed example. I didn't know this work
had progressed so far.

However, successes like this tend to beget more ambitious follow-up work
such as the type suggestions Ciprian noted. E.g. Haskell's type system
may never be finished. I know it's billed as a research language but the
same could be said of Scheme, and of every other living language to some
extent.

This is good, but it's just something to keep in mind with regards to
the SRFI process and infrastructure -- the complexity of type
definitions may increase over time and development will probably go on
indefinitely.