Would you mind elaborating why you think that Rust doesn't have a good implementation of generic types?

The signatures can get really unwieldy compared to generics in other languages. As I understand it, the Rust team is working on this.

I think you're comparing Rust to a language with ad-hoc polymorphism like C++ (where you pay for the somewhat simpler signatures with confusing template instantiation errors), and I'm very glad we didn't follow the C++ route. Rust's generics are very similar to those of Haskell.

The only major generics-related issue that is getting some significant thought is the ability to have the automatically derive the return type on top-level functions, which is not something that is common in other statically typed languages (only C++ and those with whole program type inference, which has its own set of drawbacks).

I took the Dan Grossman's PL course, so I appreciate how good Standard ML is.)