> I think it's pretty widely agreed that requiring type annotations at the function level is a good thing anyway. Apparently it's considered good practice in Haskell even though Haskell doesn't require it.

In Haskell-land: At the global scope, yes, that's considered good practice, especially if the function is exported from a module. When you just want a local helper function for some tail-recursive fun it's a bit of extra ceremony for little benefit.

(... but for Rust specifically local functions are not really a big thing, so... In Scala it can be a bit annoying, but the ol' subtyping inference undecidability thing rears its ugly head there, so there's that...)