Looks like bingo with my first search (a google for 'rrrs mailing list rational fraction float'):

https://groups.csail.mit.edu/mac/ftpdir/scheme-mail/HTML/rrr...

I've loved lisp's power since I first encountered it in the early 80s and also admired the great care put in to various aspects of Common Lisp (which is mentioned as the foundation for scheme's number decisions). Great stuff and still very relevant.

:)