Typed Clojure
Ambrose Bonnaire-Sergeant at Clojure/conj 2012
Ambrose Bonnaire-Sergeant presents Typed Clojure, which brings optional static type checking to Clojure. He shows the practical aspects of Typed Clojure, including better error messages, null-safe and array-covariance-safe Java interop, and fine-grained function invariant checking.