* Shachaf Ben-Kiki
Bah, I hadn't thought of kind polymorphism. That's a problem -- though is it a problem for any use of Typeable in base?
Yes — the plan is to make Typeable itself kind-polymorphic (instead of Typeable1, Typeable2, ...). For that you need a kind-polymorphic proxy.
For the second point, at least the type of typeRep would be pretty self-documenting, because it would be polymorphic in the "proxy" type, not mention Maybe explicitly. Maybe you mean that use sites perhaps wouldn't be? The situation wouldn't really be different from how typeOf is used currently. But maybe that's not a good benchmark. Oh well.
I was referring to user-written functions which disambugate the types by taking proxies as arguments. They may take several arguments, and it may not be obvious that some of them are just proxies. So even if Maybe would be a good fit for typeOf, it's a poor substitute for Proxy in general. (But I see now that you were only concerned with base.) Roman