I disagree — I am refactoring a large project (60k LOC, that's a lot in the Clojure world!) continuously and find that a type system would just get in the way.

I disagree — I am refactoring a large project (60k LOC, that's a lot in the Clojure world!) continuously and find that a type system would just get in the way. On the other hand, clojure.spec together with :pre/:post conditions works great and helps me a lot by checking things that no type system would verify (such as validity constraints on entire data structures). Error messages stopped being a problem with Clojure 1.10.