It looks like something like that is indeed possible. See a post on the rust internals forum where that's setup with a type alias. It was called `Fallible` in t

It looks like something like that is indeed possible. See a post on the rust internals forum where that's setup with a type alias. It was called `Fallible` in that post, but it's common in the Rust ecosystem to override the default Result type with a custom error parameter but still calling it Result. https://internals.rust-lang.org/t/make-stds-result-a-type-alias-with-default-type-parameters/4619/5 https://internals.rust-lang.org/t/make-stds-result-a-type-al... So I'd guess in this driver that the Result type being used is a type alias defined in the prelude that's glob imported.