Clojure only provides immutable data structures. Java, however, provides many mutable data structures which are readily available to Clojure. Clojure also provi

Clojure only provides immutable data structures. Java, however, provides many mutable data structures which are readily available to Clojure. Clojure also provides mutable reference types that are tuned for particular concurrency patterns. Atoms for synchronous compare-and-swap, agents for asynchronous queues, etc. There are no annotations to specify immutability, you have to trust whoever implemented the class you're using to provide the guarantees that are in their documentation. To some extent, that makes this a static vs dynamic typing discussion, but my point is that type annotations are realistically not necessary if you chose immutability as the default and provide a limited set of well known mutation operations. These operations are generally annotated with a "@", "!", or "." for "dereference current value", "side effectful", and "java interop" respectively.