That's a very good thing for a language to have, indeed. But Go isn't the best thing to look into for productivity-via-the-type-system. What is (barring the purely functional languages' learning curve) is most any ML descendant; albeit Rust in particular if Go-like performance is desirable.
In addition to typeclasses, Rust has discriminated unions (ergo algebraic datatypes), structural pattern matching, first-class functions, local type inference, and an exclusive/nonexclusive dichotomy of references which serves as a useful proxy for mutability.
