Actually, clojure compiles down to java classes, which are statically typed. Existing java types can be extended with clojure protocols. The link below talks about this, specifically about the expression problem.

See https://www.ibm.com/developerworks/library/j-clojure-protoco...

However, I learnt something. I didn't know that the definition of the expression problem required static typing. I prefer to think of it as adding static types to multiple dispatch.