Hi Asher, good question! I've been waiting in case 'former members' might respond.

You're presumably aware of Wadler's 'Proposal: Overloading in Haskell' 1988
that originally appeared on fplangc. Link from
https://homepages.inf.ed.ac.uk/wadler/topics/type-classes.html

I've tried the wayback machineĀ for fplangc@cs.ucl.ac.uk, but got nothing useful.

The repository I dig through is on wayback (various save dates)
http://web.archive.org/web/20151208175102/http://code.haskell.org/~dons/haskell-1990-2000/threads.html#00072
The earliest 1990 threads are clearly continuations from somewhere.
If ~dons (Don Stewart) kept archives of those, they're defeating my google-fu.

But hmmm, wayback is unreliable: it can peremptorily just delete stuff if it gets a copyright strike, or for no apparent reason.

The Haskell developers (for Hugs and ghc) generally published papers with the motivations for their innovations.
What additional to that thinking do you hope to find in the mailing lists?

Good luck!

AntC